Rainbow Electronics AT90LS8535 User Manual

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Features

• AVR

• Data and Nonvolatile Program Memories

• Peripheral Features

• Special Microcontroller Features

• Power Consumption at 4 MHz, 3V, 20°C

• I/O and Packages

• Operating Voltages

• Speed Grades:

– High-performance and Low-power RISC Architecture – 118 Powerful Instructions – Most Single Clock Cycle Execution – 32 x 8 General-purpose Working Registers – Up to 8 MIPS Throughput at 8 MHz

– 8K Bytes of In-System Programmable Flash

SPI Serial Interface for In-System Programming Endurance: 1,000 Write/Erase Cycles

– 512 Bytes EEPROM

Endurance: 100,000 Write/Erase Cycles – 512 Bytes Internal SRAM – Programming Lock for Software Security

– 8-channel, 10-bit ADC – Programmable UART – Master/Slave SPI Serial Interface – Two 8-bit Timer/Counters with Separate Prescaler and Compare Mode – One 16-bit Timer/Counter with Separate Prescaler, Compare and

Capture Modes and Dual 8-, 9-, or 10-bit PWM – Programmable Watchdog Timer with On-chip Oscillator – On-chip Analog Comparator

– Power-on Reset Circuit – Real-time Clock (RTC) with Separate Oscillator and Counter Mode – External and Internal Interrupt Sources – Three Sleep Modes: Idle, Power Save and Power-down

– Active: 6.4 mA – Idle Mode: 1.9 mA – Power-down Mode: <1 µA

– 32 Programmable I/O Lines – 40-lead PDIP, 44-lead PLCC, 44-lead TQFP, and 44-pad MLF

–V

: 4.0 - 6.0V AT90S8535

: 2.7 - 6.0V AT90LS8535

–V

– 0 - 8 MHz for the AT90S8535 – 0 - 4 MHz for the AT90LS8535

8-bit Microcontroller with 8K Bytes In-System Programmable Flash

AT90S8535 AT90LS8535

Rev. 1041H–11/01

Pin Configurations

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Description The AT90S8535 is a low-power CMOS 8-bit microcontroller based on the AVR RISC

architecture. By executing powerful instructions in a single clock cycle, the AT90S8535 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed.

Block Diagram Figure 1. The AT90S8535 Block Diagram

PA0 - PA7

VCC

PC0 - PC7

GND

AVCC

AGND AREF

DATA REGISTER

PROGRAM COUNTER

PROGRAM

FLASH

INSTRUCTION

DECODER

CONTROL

LINES

PORTA DRIVERS

DATA DIR.

PORTA

ANALOG MUX ADC

REG. PORTA

STACK

POINTER

SRAM

GENERAL PURPOSE

REGISTERS

X Y Z

ALU

8-BIT DATA BUS

PORTC DRIVERS

DATA REGISTER

PORTC

INTERNAL

OSCILLATOR

WATCHDOG

TIMER

MCU CONTROL

TIMER/

COUNTERS

INTERRUPT

UNIT

EEPROM

DATA DIR.

REG. PORTC

OSCILLATOR

TIMING AND

CONTROL

XTAL1

XTAL2

RESET

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PROGRAMMING

LOGIC

ANALOG

DATA REGISTER

ARATOR

COMP

PORTB

PORTB DRIVERS

STATUS

SPI

PB0 - PB7

DATA DIR.

REG. PORTB

UART

DATA REGISTER

PORTD

PORTD DRIVERS

PD0 - PD7

DATA DIR.

REG. PORTD

The AVR core combines a rich instruction set with 32 general-purpose working registers. All the 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be accessed in one single instruction executed in one clock cycle. The resulting architecture is more code efficient while achieving throughputs up to ten times faster than conventional CISC microcontrollers.

The AT90S8535 provides the following features: 8K bytes of In-System Programmable Flash, 512 bytes EEPROM, 512 bytes SRAM, 32 general-purpose I/O lines, 32 generalpurpose working registers, Real-time Clock (RTC), three flexible timer/counters with compare modes, internal and external interrupts, a programmable serial UART, 8-channel, 10-bit ADC, programmable Watchdog Timer with internal oscillator, an SPI serial port and three software-selectable power-saving modes. The Idle Mode stops the CPU while allowing the SRAM, timer/counters, SPI port and interrupt system to continue functioning. The Power-down mode saves the register contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset. In Power Save Mode, the timer oscillator continues to run, allowing the user to maintain a timer base while the rest of the device is sleeping.

The device is manufactured using Atmel’s high-density nonvolatile memory technology. The On-chip ISP Flash allows the program memory to be reprogrammed in-system through an SPI serial interface or by a conventional nonvolatile memory programmer. By combining an 8-bit RISC CPU with In-System Programmable Flash on a monolithic chip, the Atmel AT90S8535 is a powerful microcontroller that provides a highly flexible and cost effective solution to many embedded control applications.

The AT90S8535 AVR is supported with a full suite of program and system development tools including: C compilers, macro assemblers, program debugger/simulators, in-circuit emulators and evaluation kits.

Pin Descriptions

VCC Digital supply voltage.

GND Digital ground.

Port A (PA7..PA0) Port A is an 8-bit bi-directional I/O port. Port pins can provide internal pull-up resistors

(selected for each bit). The Port A output buffers can sink 20 mA and can drive LED displays directly. When pins PA0 to PA7 are used as inputs and are externally pulled low, they will source current if the internal pull-up resistors are activated.

Port A also serves as the analog inputs to the A/D Converter.

The Port A pins are tri-stated when a reset condition becomes active, even if the clock is not running.

Port B (PB7..PB0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port B output

buffers can sink 20 mA. As inputs, Port B pins that are externally pulled low will source current if the pull-up resistors are activated. Port B also serves the functions of various special features of the AT90S8535 as listed on page 78.

The Port B pins are tri-stated when a reset condition becomes active, even if the clock is not running.

Port C (PC7..PC0) Port C is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port C output

buffers can sink 20 mA. As inputs, Port C pins that are externally pulled low will source

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current if the pull-up resistors are activated. Two Port C pins can alternatively be used as oscillator for Timer/Counter2.

The Port C pins are tri-stated when a reset condition becomes active, even if the clock is not running.

Port D (PD7..PD0) Port D is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port D output

buffers can sink 20 mA. As inputs, Port D pins that are externally pulled low will source current if the pull-up resistors are activated.

Port D also serves the functions of various special features of the AT90S8535 as listed on page 86.

The Port D pins are tri-stated when a reset condition becomes active, even if the clock is not running.

RESET

XTAL1 Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2 Output from the inverting oscillator amplifier.

AVCC AVCC is the supply voltage pin for Port A and the A/D Converter. If the ADC is not used,

AREF AREF is the analog reference input for the A/D Converter. For ADC operations, a volt-

AGND Analog ground. If the board has a separate analog ground plane, this pin should be con-

Reset input. An external reset is generated by a low level on the RESET pin. Reset pulses longer than 50 ns will generate a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate a reset.

this pin must be connected to VCC. If the ADC is used, this pin must be connected to VCC via a low-pass filter. See page 68 for details on operation of the ADC.

age in the range 2V to AV

nected to this ground plane. Otherwise, connect to GND.

must be applied to this pin.

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Clock Options

Crystal Oscillator XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can

be configured for use as an on-chip oscillator, as shown in Figure 2. Either a quartz crystal or a ceramic resonator may be used.

Figure 2. Oscillator Connections

MAX 1 HC BUFFER

Note: When using the MCU Oscillator as a clock for an external device, an HC buffer should be

connected as indicated in the figure.

External Clock To drive the device from an external clock source, XTAL2 should be left unconnected

while XTAL1 is driven as shown in Figure 3.

Figure 3. External Clock Drive Configuration

XTAL2

XTAL1

GND

Timer Oscillator For the Timer Oscillator pins, TOSC1 and TOSC2, the crystal is connected directly

between the pins. No external capacitors are needed. The oscillator is optimized for use with a 32,768 Hz watch crystal. Applying an external clock source to TOSC1 is not recommended.

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Architectural Overview

The fast-access register file concept contains 32 x 8-bit general-purpose working registers with a single clock cycle access time. This means that during one single clock cycle, one Arithmetic Logic Unit (ALU) operation is executed. Two operands are output from the register file, the operation is executed and the result is stored back in the register file – in one clock cycle.

Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data Space addressing, enabling efficient address calculations. One of the three address pointers is also used as the address pointer for the constant table look-up function. These added function registers are the 16-bit X-register, Y-register, and Z-register.

Figure 4. The AT90S8535 AVR RISC Architecture

Data Bus 8-bit

4K X 16

Program

Memory

Instruction

Decoder

Control Lines

Program

Counter

Direct Addressing

Status

and Control

32 x 8 General Purpose

Registrers

ALU

Indirect Addressing

512 x 8

Data

SRAM

Interrupt

Unit

SPI

Unit

Serial

UART

8-bit

Timer/Counter

16-bit

Timer/Counter

with PWM

8-bit

Timer/Counter

with PWM

Watchdog

Timer

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512 x 8

EEPROM

I/O Lines

Analog to Digital

Converter

Analog

Comparator

The ALU supports arithmetic and logic functions between registers or between a constant and a register. Single register operations are also executed in the ALU. Figure 4 shows the AT90S8535 AVR RISC microcontroller architecture.

In addition to the register operation, the conventional memory addressing modes can be used on the register file as well. This is enabled by the fact that the register file is

assigned the 32 lowermost Data Space addresses ($00 - $1F), allowing them to be accessed as though they were ordinary memory locations.

The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers, Timer/Counters, A/D converters and other I/O functions. The I/O memory can be accessed directly or as the Data Space locations following those of the register file, $20 - $5F.

The AVR uses a Harvard architecture concept – with separate memories and buses for program and data. The program memory is executed with a two-stage pipeline. While one instruction is being executed, the next instruction is pre-fetched from the program memory. This concept enables instructions to be executed in every clock cycle. The program memory is in-system downloadable Flash memory.

With the relative jump and call instructions, the whole 4K address space is directly accessed. Most AVR instructions have a single 16-bit word format. Every program memory address contains a 16- or 32-bit instruction.

During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the stack. The stack is effectively allocated in the general data SRAM and consequently, the stack size is only limited by the total SRAM size and the usage of the SRAM. All user programs must initialize the SP in the reset routine (before subroutines or interrupts are executed). The 10-bit stack pointer (SP) is read/write-accessible in the I/O space.

The 512 bytes data SRAM can be easily accessed through the five different addressing modes supported in the AVR architecture.

The memory spaces in the AVR architecture are all linear and regular memory maps.

Figure 5. Memory Maps

Program Flash

(4K x 16)

$000

$FFF

Data MemoryProgram Memory

32 Gen. Purpose

Working Registers

64 I/O Registers

Internal SRAM

(512 x 8)

$0000

$001F $0020

$005F $0060

$025F

Data Memory

$000

EEPROM

(512 x 8)

$1FF

A flexible interrupt module has its control registers in the I/O space with an additional global interrupt enable bit in the status register. All the different interrupts have a separate interrupt vector in the interrupt vector table at the beginning of the program

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memory. The different interrupts have priority in accordance with their interrupt vector position. The lower the interrupt vector address, the higher the priority.

General-purpose Register File

Figure 6 shows the structure of the 32 general-purpose working registers in the CPU.

Figure 6. AVR CPU General-purpose Working Registers

70Addr.

R0 $00

R1 $01

R2 $02

…

R13 $0D

General R14 $0E

Purpose R15 $0F

Working R16 $10

Registers R17 $11

…

R26 $1A X-register low byte

R27 $1B X-register high byte

R28 $1C Y-register low byte

R29 $1D Y-register high byte

R30 $1E Z-register low byte

R31 $1F Z-register high byte

All the register operating instructions in the instruction set have direct and single-cycle access to all registers. The only exception is the five constant arithmetic and logic instructions SBCI, SUBI, CPI, ANDI and ORI between a constant and a register and the LDI instruction for load immediate constant data. These instructions apply to the second half of the registers in the register file (R16..R31). The general SBC, SUB, CP, AND, and OR and all other operations between two registers or on a single register apply to the entire register file.

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As shown in Figure 6, each register is also assigned a data memory address, mapping them directly into the first 32 locations of the user Data Space. Although not being physically implemented as SRAM locations, this memory organization provides great flexibility in access of the registers, as the X-, Y-, and Z-registers can be set to index any register in the file.

X-register, Y-register and Zregister

The registers R26..R31 have some added functions to their general-purpose usage. These registers are address pointers for indirect addressing of the Data Space. The three indirect address registers, X, Y, and Z, are defined in Figure 7.

Figure 7. X-, Y-, and Z-register

15 0

X-register 7 0

R27 ($1B) R26 ($1A)

15 0

Y-register

Z-register

7 0 7 0

R29 ($1D) R28 ($1C)

15 0

7 0 7 0

R31 ($1F) R30 ($1E)

7 0

In the different addressing modes, these address registers have functions as fixed displacement, automatic increment and decrement (see the descriptions for the different instructions).

ALU – Arithmetic Logic Unit

In-System Programmable Flash Program Memory

The high-performance AVR ALU operates in direct connection with all the 32 generalpurpose working registers. Within a single clock cycle, ALU operations between registers in the register file are executed. The ALU operations are divided into three main categories: arithmetic, logical and bit functions.

The AT90S8535 contains 8K bytes On-chip, In-System Programmable Flash memory for program storage. Since all instructions are 16- or 32-bit words, the Flash is organized as 4K x 16. The Flash memory has an endurance of at least 1000 write/erase cycles. The AT90S8535 Program Counter (PC) is 12 bits wide, thus addressing the 4096 program memory addresses.

See page 99 for a detailed description on Flash data downloading.

See page 12 for the different program memory addressing modes.

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SRAM Data Memory Figure 8 shows how the AT90S8535 SRAM memory is organized.

Figure 8. SRAM Organization

R0 R1 R2

...

Data Address Space

$0000 $0001 $0002

...

R29 R30 R31

I/O Registers

$00 $01 $02

...

$3D $3E $3F

$001D $001E

$001F

$0020 $0021 $0022

...

$005D $005E $005F

Internal SRAM

$0060 $0061

...

$025E $025F

The lower 608 data memory locations address the Register file, the I/O memory and the internal data SRAM. The first 96 locations address the Register file + I/O memory, and the next 512 locations address the internal data SRAM.

The five different addressing modes for the data memory cover: Direct, Indirect with Displacement, Indirect, Indirect with Pre-decrement and Indirect with Post-increment. In the register file, registers R26 to R31 feature the indirect addressing pointer registers.

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The direct addressing reaches the entire data space.

The Indirect with Displacement mode features 63 address locations reached from the base address given by the Y- or Z-registers.

When using register indirect addressing modes with automatic pre-decrement and postincrement, the address registers X, Y, and Z are decremented and incremented.

The 32 general-purpose working registers, 64 I/O registers and the 512 bytes of internal data SRAM in the AT90S8535 are all accessible through all these addressing modes.

See the next section for a detailed description of the different addressing modes.

Program and Data Addressing Modes

The AT90S8535 AVR RISC microcontroller supports powerful and efficient addressing modes for access to the program memory (Flash) and data memory (SRAM, register file and I/O memory). This section describes the different addressing modes supported by the AVR architecture. In the figures, OP means the operation code part of the instruction word. To simplify, not all figures show the exact location of the addressing bits.

Register Direct, Single Register Rd

Register Direct, Two Registers Rd And Rr

Figure 9. Direct Single Register Addressing

The operand is contained in register d (Rd).

Figure 10. Direct Register Addressing, Two Registers

Operands are contained in register r (Rr) and d (Rd). The result is stored in register d (Rd).

I/O Direct Figure 11. I/O Direct Addressing

Operand address is contained in six bits of the instruction word. n is the destination or source register address.

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Data Direct Figure 12. Direct Data Addressing

OP Rr/Rd

15 0

20 19

16 LSBs

A 16-bit data address is contained in the 16 LSBs of a 2-word instruction. Rd/Rr specify the destination or source register.

AT90S/LS8535

Data Space

$0000

$025F

Data Indirect with

Figure 13. Data Indirect with Displacement

Displacement

Y OR Z - REGISTER

OP an

Operand address is the result of the Y- or Z-register contents added to the address contained in six bits of the instruction word.

Data Indirect Figure 14. Data Indirect Addressing

X, Y OR Z - REGISTER

Data Space

05610

Data Space

015

$0000

025F

$0000

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$025F

Operand address is the contents of the X-, Y-, or the Z-register.

Data Indirect with Predecrement

Figure 15. Data Indirect Addressing with Pre-decrement

Data Space

015

X, Y OR Z - REGISTER

-1

$0000

$025F

The X-, Y-, or the Z-register is decremented before the operation. Operand address is the decremented contents of the X-, Y-, or the Z-register.

Data Indirect with Postincrement

Constant Addressing Using the LPM Instruction

Figure 16. Data Indirect Addressing with Post-increment

Data Space

015

X, Y OR Z - REGISTER

$0000

$025F

The X-, Y-, or the Z-register is incremented after the operation. Operand address is the content of the X-, Y-, or the Z-register prior to incrementing.

Figure 17. Code Memory Constant Addressing

$FFF

Constant byte address is specified by the Z-register contents. The 15 MSBs select word address (0 - 4K), the LSB selects low byte if cleared (LSB = 0) or high byte if set (LSB =

1).

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Indirect Program Addressing, IJMP and ICALL

Relative Program Addressing, RJMP and RCALL

Figure 18. Indirect Program Memory Addressing

$FFF

Program execution continues at address contained by the Z-register (i.e., the PC is loaded with the contents of the Z-register).

Figure 19. Relative Program Memory Addressing

$FFF

Program execution continues at address PC + k + 1. The relative address k is from 2048 to 2047.

EEPROM Data Memory The AT90S8535 contains 512 bytes of data EEPROM memory. It is organized as a sep-

arate data space, in which single bytes can be read and written. The EEPROM has an endurance of at least 100,000 write/erase cycles. The access between the EEPROM and the CPU is described on page 51 specifying the EEPROM address registers, the EEPROM data register and the EEPROM control register.

For the SPI data downloading, see page 99 for a detailed description.

Memory Access Times and Instruction Execution Timing

This section describes the general access timing concepts for instruction execution and internal memory access.

The AVR CPU is driven by the System Clock Ø, directly generated from the external clock crystal for the chip. No internal clock division is used.

Figure 20 shows the parallel instruction fetches and instruction executions enabled by the Harvard architecture and the fast-access register file concept. This is the basic pipelining concept to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost, functions per clocks and functions per power-unit.

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Figure 20. The Parallel Instruction Fetches and Instruction Executions

T1 T2 T3 T4

System Clock Ø

1st Instruction Fetch

1st Instruction Execute

2nd Instruction Fetch

2nd Instruction Execute

3rd Instruction Fetch

3rd Instruction Execute

4th Instruction Fetch

Figure 21 shows the internal timing concept for the register file. In a single clock cycle an ALU operation using two register operands is executed and the result is stored back to the destination register.

Figure 21. Single Cycle ALU Operation

T1 T2 T3 T4

System Clock Ø

Total Execution Time

ALU Operation Execute

Result Write Back

The internal data SRAM access is performed in two System Clock cycles as described in Figure 22.

Figure 22. On-chip Data SRAM Access Cycles

T1 T2 T3 T4

System Clock Ø

Address

Data

Prev. Address

Address

Write

Read

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I/O Memory The I/O space definition of the AT90S8535 is shown in Table 1.

Table 1. AT90S8535 I/O Space

I/O Address

(SRAM Address) Name Function

$3F ($5F) SREG Status REGister

$3E ($5E) SPH Stack Pointer High

$3D ($5D) SPL Stack Pointer Low

$3B ($5B) GIMSK General Interrupt MaSK register

$3A ($5A) GIFR General Interrupt Flag Register

$39 ($59) TIMSK Timer/Counter Interrupt MaSK register

$38 ($58) TIFR Timer/Counter Interrupt Flag register

$35 ($55) MCUCR MCU general Control Register

$34 ($45) MCUSR MCU general Status Register

$33 ($53) TCCR0 Timer/Counter0 Control Register

$32 ($52) TCNT0 Timer/Counter0 (8-bit)

$2F ($4F) TCCR1A Timer/Counter1 Control Register A

$2E ($4E) TCCR1B Timer/Counter1 Control Register B

$2D ($4D) TCNT1H Timer/Counter1 High Byte

$2C ($4C) TCNT1L Timer/Counter1 Low Byte

$2B ($4B) OCR1AH Timer/Counter1 Output Compare Register A High Byte

$2A ($4A) OCR1AL Timer/Counter1 Output Compare Register A Low Byte

$29 ($49) OCR1BH Timer/Counter1 Output Compare Register B High Byte

$28 ($48) OCR1BL Timer/Counter1 Output Compare Register B Low Byte

$27 ($47) ICR1H T/C 1 Input Capture Register High Byte

$26 ($46) ICR1L T/C 1 Input Capture Register Low Byte

$25 ($45) TCCR2 Timer/Counter2 Control Register

$24 ($44) TCNT2 Timer/Counter2 (8-bit)

$23 ($43) OCR2 Timer/Counter2 Output Compare Register

$22 ($42) ASSR Asynchronous Mode Status Register

$21 ($41) WDTCR Watchdog Timer Control Register

$1F ($3E) EEARH EEPROM Address Register High Byte

$1E ($3E) EEARL EEPROM Address Register Low Byte

$1D ($3D) EEDR EEPROM Data Register

$1C ($3C) EECR EEPROM Control Register

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$1B ($3B) PORTA Data Register, Port A

$1A ($3A) DDRA Data Direction Register, Port A

$19 ($39) PINA Input Pins, Port A

$18 ($38) PORTB Data Register, Port B

Table 1. AT90S8535 I/O Space (Continued)

I/O Address

(SRAM Address) Name Function

$17 ($37) DDRB Data Direction Register, Port B

$16 ($36) PINB Input Pins, Port B

$15 ($35) PORTC Data Register, Port C

$14 ($34) DDRC Data Direction Register, Port C

$13 ($33) PINC Input Pins, Port C

$12 ($32) PORTD Data Register, Port D

$11 ($31) DDRD Data Direction Register, Port D

$10 ($30) PIND Input Pins, Port D

$0F ($2F) SPDR SPI I/O Data Register

$0E ($2E) SPSR SPI Status Register

$0D ($2D) SPCR SPI Control Register

$0C ($2C) UDR UART I/O Data Register

$0B ($2B) USR UART Status Register

$0A ($2A) UCR UART Control Register

$09 ($29) UBRR UART Baud Rate Register

$08 ($28) ACSR Analog Comparator Control and Status Register

$07 ($27) ADMUX ADC Multiplexer Select Register

$06 ($26) ADCSR ADC Control and Status Register

$05 ($25) ADCH ADC Data Register High

$04 ($24) ADCL ADC Data Register Low

Note: Reserved and unused locations are not shown in the table.

All AT90S8535 I/Os and peripherals are placed in the I/O space. The I/O locations are accessed by the IN and OUT instructions transferring data between the 32 general-purpose working registers and the I/O space. I/O registers within the address range $00 -

$1F are directly bit-accessible using the SBI and CBI instructions. In these registers, the value of single bits can be checked by using the SBIS and SBIC instructions. Refer to the instruction set section for more details. When using the I/O specific commands IN and OUT, the I/O addresses $00 - $3F must be used. When addressing I/O registers as SRAM, $20 must be added to these addresses. All I/O register addresses throughout this document are shown with the SRAM address in parentheses.

For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses should never be written.

Some of the status flags are cleared by writing a logical “1” to them. Note that the CBI and SBI instructions will operate on all bits in the I/O register, writing a “1” back into any flag read as set, thus clearing the flag. The CBI and SBI instructions work with registers $00 to $1F only.

The I/O and peripherals control registers are explained in the following sections.

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Status Register – SREG The AVR Status Register (SREG) at I/O space location $3F ($5F) is defined as:

Bit 76543210

$3F ($5F) I T H S V N Z C SREG

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

• Bit 7 – I: Global Interrupt Enable

The global interrupt enable bit must be set (one) for the interrupts to be enabled. The individual interrupt enable control is then performed in separate control registers. If the global interrupt enable register is cleared (zero), none of the interrupts are enabled independent of the individual interrupt enable settings. The I-bit is cleared by hardware after an interrupt has occurred and is set by the RETI instruction to enable subsequent interrupts.

• Bit 6 – T: Bit Copy Storage

The bit copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source and destination for the operated bit. A bit from a register in the register file can be copied into T by the BST instruction and a bit in T can be copied into a bit in a register in the register file by the BLD instruction.

• Bit 5 – H: Half-carry Flag

The half-carry flag H indicates a half-carry in some arithmetic operations. See the Instruction Set description for detailed information.

• Bit 4 – S: Sign Bit, S = N

⊄⊕ V

The S-bit is always an exclusive or between the negative flag N and the two’s complement overflow flag V. See the Instruction Set description for detailed information.

• Bit 3 – V: Two’s Complement Overflow Flag

The two’s complement overflow flag V supports two’s complement arithmetics. See the Instruction Set description for detailed information.

• Bit 2 – N: Negative Flag

The negative flag N indicates a negative result from an arithmetical or logical operation. See the Instruction Set description for detailed information.

• Bit 1 – Z: Zero Flag

The zero flag Z indicates a zero result from an arithmetical or logic operation. See the Instruction Set description for detailed information.

• Bit 0 – C: Carry Flag

The carry flag C indicates a carry in an arithmetical or logical operation. See the Instruction Set description for detailed information.

Note that the Status Register is not automatically stored when entering an interrupt routine and restored when returning from an interrupt routine. This must be handled by software.

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Stack Pointer – SP The AT90S8535 Stack Pointer is implemented as two 8-bit registers in the I/O space

locations $3E ($5E) and $3D ($5D). As the AT90S8535 data memory has $25F locations, 10 bits are used.

Bit 151413121110 9 8

$3E ($5E) ––––––SP9 SP8 SPH

$3D ($5D) SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SPL

76543210

Read/WriteRRRRRRR/WR/W

R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

00000000

The Stack Pointer points to the data SRAM stack area where the Subroutine and Interrupt stacks are located. This stack space in the data SRAM must be defined by the program before any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be set to point above $60. The Stack Pointer is decremented by 1 when data is pushed onto the stack with the PUSH instruction and it is decremented by 2 when an address is pushed onto the stack with subroutine calls and interrupts. The Stack Pointer is incremented by 1 when data is popped from the stack with the POP instruction and it is incremented by 2 when an address is popped from the stack with return from subroutine RET or return from interrupt RETI.

Reset and Interrupt Handling

The AT90S8535 provides 16 different interrupt sources. These interrupts and the separate reset vector each have a separate program vector in the program memory space. All interrupts are assigned individual enable bits that must be set (one) together with the I-bit in the Status Register in order to enable the interrupt.

The lowest addresses in the program memory space are automatically defined as the Reset and Interrupt vectors. The complete list of vectors is shown in Table 2. The list also determines the priority levels of the different interrupts. The lower the address, the higher the priority level. RESET has the highest priority, and next is INT0 (the External Interrupt Request 0), etc.

Table 2. Reset and Interrupt Vectors

Vector No. Program Address Source Interrupt Definition

Hardware Pin, Power-on Reset and

1 $000 RESET

2 $001 INT0 External Interrupt Request 0

3 $002 INT1 External Interrupt Request 1

4 $003 TIMER2 COMP Timer/Counter2 Compare Match

5 $004 TIMER2 OVF Timer/Counter2 Overflow

6 $005 TIMER1 CAPT Timer/Counter1 Capture Event

7 $006 TIMER1 COMPA Timer/Counter1 Compare Match A

8 $007 TIMER1 COMPB Timer/Counter1 Compare Match B

Watchdog Reset

9 $008 TIMER1 OVF Timer/Counter1 Overflow

10 $009 TIMER0 OVF Timer/Counter0 Overflow

11 $00A SPI, STC SPI Serial Transfer Complete

12 $00B UART, RX UART, Rx Complete

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AT90S/LS8535

Table 2. Reset and Interrupt Vectors (Continued)

Vector No. Program Address Source Interrupt Definition

13 $00C UART, UDRE UART Data Register Empty

14 $00D UART, TX UART, Tx Complete

15 $00E ADC ADC Conversion Complete

16 $00F EE_RDY EEPROM Ready

17 $010 ANA_COMP Analog Comparator

The most typical and general program setup for the Reset and Interrupt vector addresses are:

Address Labels Code Comments

$000 rjmp RESET ; Reset Handler

$001 rjmp EXT_INT0 ; IRQ0 Handler

$002 rjmp EXT_INT1 ; IRQ1 Handler

$003 rjmp TIM2_COMP ; Timer2 Compare Handler

$004 rjmp TIM2_OVF ; Timer2 Overflow Handler

$005 rjmp TIM1_CAPT ; Timer1 Capture Handler

$006 rjmp TIM1_COMPA ; Timer1 CompareA Handler

$007 rjmp TIM1_COMPB ; Timer1 CompareB Handler

$008 rjmp TIM1_OVF ; Timer1 Overflow Handler

$009 rjmp TIM0_OVF ; Timer0 Overflow Handler

$00a rjmp SPI_STC; ; SPI Transfer Complete Handler

$00b rjmp UART_RXC ; UART RX Complete Handler

$00c rjmp UART_DRE ; UDR Empty Handler

$00d rjmp UART_TXC ; UART TX Complete Handler

$00e rjmp ADC ; ADC Conversion Complete Interrupt Handler

$00f rjmp EE_RDY ; EEPROM Ready Handler

$010 rjmp ANA_COMP ; Analog Comparator Handler

$011 MAIN: ldi r16, high(RAMEND); Main program start

$012 out SPH,r16

$013 ldi r16, low(RAMEND) ;

$014 out SPL,r16

$015 <instr> xxx

…… ……

Reset Sources The AT90S8535 has three sources of reset:

• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on

Reset threshold (V

POT

• External Reset. The MCU is reset when a low level is present on the RESET pin for

more than 50 ns.

• Watchdog Reset. The MCU is reset when the Watchdog timer period expires and

the Watchdog is enabled.

During reset, all I/O registers are set to their initial values and the program starts execution from address $000. The instruction placed in address $000 must be an RJMP (relative jump) instruction to the reset handling routine. If the program never enables an interrupt source, the interrupt vectors are not used and regular program code can be

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placed at these locations. The circuit diagram in Figure 23 shows the reset logic. Table 3 defines the timing and electrical parameters of the reset circuitry.

Figure 23. Reset Logic

Table 3. Reset Characteristics (V

Symbol Parameter Min Typ Max Units

(1)

POT

RST

TOUT

Note: 1. The Power-on Reset will not work unless the supply voltage has been below V

Power-on Reset Threshold (rising) 1.0 1.4 1.8 V

Power-on Reset Threshold (falling) 0.4 0.6 0.8 V

RESET Pin Threshold Voltage 0.6 V

Reset Delay Time-out Period FSTRT Unprogrammed

Reset Delay Time-out Period FSTRT Programmed

(falling).

= 5.0V)

11.0 16.0 21.0 ms

1.0 1.1 1.2 ms

POT

Table 4. Number of Watchdog Oscillator Cycles

FSTRT Time-out at VCC = 5V Number of WDT Cycles

Programmed 1.1 ms 1K

Unprogrammed 16.0 ms 16K

Power-on Reset A Power-on Reset (POR) circuit ensures that the device is reset from power-on. As

shown in Figure 23, an internal timer clocked from the Watchdog Timer oscillator prevents the MCU from starting until after a certain period after V on Threshold voltage (V

), regardless of the VCC rise time (see Figure 24).

POT

has reached the Power-

The user can select the start-up time according to typical oscillator start-up time. The number of WDT oscillator cycles is shown in Table 4. The frequency of the Watchdog oscillator is voltage-dependent as shown in “Typical Characteristics” on page 107.

If the built-in start-up delay is sufficient, RESET an external pull-up resistor. By holding the pin low for a period after V applied, the Power-on Reset period can be extended. Refer to Figure 25 for a timing example of this.

AT90S/LS8535

can be connected to VCC directly or via

has been

1041H–11/01

Figure 24. MCU Start-up, RESET Tied to VCC.

VCC

RESET

TIME-OUT

INTERNAL

RESET

POT

RST

TOUT

AT90S/LS8535

Figure 25. MCU Start-up, RESET

VCC

RESET

TIME-OUT

INTERNAL

RESET

POT

Controlled Externally

RST

TOUT

External Reset An external reset is generated by a low level on the RESET

than 50 ns will generate a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate a reset. When the applied signal reaches the Reset Threshold Voltage (V period t

) on its positive edge, the delay timer starts the MCU after the Time-out

RST

has expired.

TOUT

Figure 26. External Reset during Operation

pin. Reset pulses longer

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Watchdog Reset When the Watchdog times out, it will generate a short reset pulse of 1 XTAL cycle dura-

tion. On the falling edge of this pulse, the delay timer starts counting the Time-out period

. Refer to page 49 for details on operation of the Watchdog.

TOUT

Figure 27. Watchdog Reset during Operation

MCU Status Register – MCUSR

The MCU Status Register provides information on which reset source caused an MCU reset.

Bit 76543210

$34 ($54) ––––––EXTRF PORF MCUSR

Read/WriteRRRRRRR/WR/W

Initial Value000000See Bit Description

• Bits 7..2 – Res: Reserved Bits

These bits are reserved bits in the AT90S8535 and always read as zero.

• Bit 1 – EXTRF: External Reset Flag

After a power-on reset, this bit is undefined (X). It can only be set by an External Reset. A Watchdog Reset will leave this bit unchanged. The bit is cleared by writing a logical zero to the bit.

• Bit 0 – PORF: Power-on Reset Flag

This bit is only set by a Power-on Reset. A Watchdog Reset or an External Reset will leave this bit unchanged. The bit is cleared by writing a logical zero to the bit.

To summarize, Table 5 shows the value of these two bits after the three modes of reset.

Table 5. PORF and EXTRF Values after Reset

Reset Source EXTRF PORF

Power-on Reset Undefined 1

External Reset 1 Unchanged

Watchdog Reset Unchanged Unchanged

To make use of these bits to identify a reset condition, the user software should clear both the PORF and EXTRF bits as early as possible in the program. Checking the PORF and EXTRF values is done before the bits are cleared. If the bit is cleared before an External or Watchdog Reset occurs, the source of reset can be found by using Table

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AT90S/LS8535

Table 6. Reset Source Identification

EXTRF PORF Reset Source

0 0 Watchdog Reset

0 1 Power-on Reset

1 0 External Reset

1 1 Power-on Reset

Interrupt Handling The AT90S8535 has two 8-bit interrupt mask control registers: GIMSK (General Inter-

rupt Mask register) and TIMSK (Timer/Counter Interrupt Mask register).

When an interrupt occurs, the Global Interrupt Enable I-bit is cleared (zero) and all interrupts are disabled. The user software can set (one) the I-bit to enable nested interrupts. The I-bit is set (one) when a Return from Interrupt instruction (RETI) is executed.

When the Program Counter is vectored to the actual interrupt vector in order to execute the interrupt handling routine, hardware clears the corresponding flag that generated the interrupt. Some of the interrupt flags can also be cleared by writing a logical “1” to the flag bit position(s) to be cleared. If an interrupt condition occurs when the corresponding interrupt enable bit is cleared (zero), the interrupt flag will be set and remembered until the interrupt is enabled or the flag is cleared by software.

General Interrupt Mask Register – GIMSK

If one or more interrupt conditions occur when the global interrupt enable bit is cleared (zero), the corresponding interrupt flag(s) will be set and remembered until the global interrupt enable bit is set (one) and will be executed by order of priority.

Note that external level interrupt does not have a flag and will only be remembered for as long as the interrupt condition is active.

Note that the Status Register is not automatically stored when entering an interrupt routine and restored when returning from an interrupt routine. This must be handled by software.

Bit 7 6 5 4 3 2 1 0

$3B ($5B) INT1 INT0 –– ––––GIMSK

Read/Write R/W R/W R R R R R R

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – INT1: External Interrupt Request 1 Enable

When the INT1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the external pin interrupt is enabled. The Interrupt Sense Control1 bits 1/0 (ISC11 and ISC10) in the MCU general Control Register (MCUCR) define whether the external interrupt is activated on rising or falling edge of the INT1 pin or level sensed. Activity on the pin will cause an interrupt request even if INT1 is configured as an output. The corresponding interrupt of External Interrupt Request 1 is executed from program memory address $002. See also “External Interrupts.”

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• Bit 6 – INT0: External Interrupt Request 0 Enable

When the INT0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the external pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and ISC00) in the MCU general Control Register (MCUCR) define whether the external interrupt is activated on rising or falling edge of the INT0 pin or level sensed. Activity on the pin will cause an interrupt request even if INT0 is configured as an output. The corre-

General Interrupt Flag Register – GIFR

sponding interrupt of External Interrupt Request 0 is executed from program memory address $001. See also “External Interrupts.”

• Bits 5.0 – Res: Reserved Bits

These bits are reserved bits in the AT90S8535 and always read as zero.

Bit 7 6 5 4 3 2 1 0

$3A ($5A) INTF1 INTF0 –– ––––GIFR

Read/Write R/W R/W R R R R R R

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – INTF1: External Interrupt Flag1

When an edge or logical change on the INT1 pin triggers an interrupt request, INTF1 becomes set (one). This flag is always cleared (0) when the pin is configured for lowlevel interrupts, as the state of a low-level interrupt can be determined by reading the PIN register.

If the I-bit in SREG and the INT1 bit in GIMSK are set (one), the MCU will jump to the interrupt address $002. For edge and logic change interrupts, this flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical “1” to it.

• Bit 6 – INTF0: External Interrupt Flag0

When an edge or logical change on the INT0 pin triggers an interrupt request, INTF0 becomes set (one). This flag is always cleared (0) when the pin is configured for lowlevel interrupts, as the state of a low-level interrupt can be determined by reading the PIN register.

Timer/Counter Interrupt Mask Register – TIMSK

If the I-bit in SREG and the INT0 bit in GIMSK are set (one), the MCU will jump to the interrupt address $001. For edge and logic change interrupts, this flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical “1” to it.

• Bits 5..0 – Res: Reserved Bits

These bits are reserved bits in the AT90S8535 and always read as zero.

Bit 7 6 5 4 3 2 1 0

$39 ($59) OCIE2 TOIE2 TICIE1 OCIE1A OCIE1B TOIE1 – TOIE0 TIMSK

Read/Write R/W R/W R/W R/W R/W R/W R R/W

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – OCIE2: Timer/Counter2 Output Compare Match Interrupt Enable

When the OCIE2 bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter2 Compare Match interrupt is enabled. The corresponding interrupt (at vector $003) is executed if a compare match in Timer/Counter2 occurs (i.e., when the OCF2 bit is set in the Timer/Counter Interrupt Flag Register [TIFR]).

• Bit 6 – TOIE2: Timer/Counter2 Overflow Interrupt Enable

When the TOIE2 bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter2 Overflow interrupt is enabled. The corresponding interrupt (at vector $004) is executed if an overflow in Timer/Counter2 occurs (i.e., when the TOV2 bit is set in the Timer/Counter Interrupt Flag Register [TIFR]).

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AT90S/LS8535

• Bit 5 – TICIE1: Timer/Counter1 Input Capture Interrupt Enable

When the TICIE1 bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter1 Input Capture Event Interrupt is enabled. The corresponding interrupt (at vector $005) is executed if a capture-triggering event occurs on pin 20, PD6 (ICP) (i.e., when the ICF1 bit is set in the Timer/Counter Interrupt Flag Register [TIFR]).

• Bit 4 – OCIE1A: Timer/Counter1 Output CompareA Match Interrupt Enable

When the OCIE1A bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter1 CompareA Match interrupt is enabled. The corresponding interrupt (at vector $006) is executed if a CompareA match in Timer/Counter1 occurs (i.e., when the OCF1A bit is set in the Timer/Counter Interrupt Flag Register [TIFR]).

• Bit 3 – OCIE1B: Timer/Counter1 Output CompareB Match Interrupt Enable

When the OCIE1B bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter1 CompareB Match interrupt is enabled. The corresponding interrupt (at vector $007) is executed if a CompareB match in Timer/Counter1 occurs (i.e., when the OCF1B bit is set in the Timer/Counter Interrupt Flag Register [TIFR]).

• Bit 2 – TOIE1: Timer/Counter1 Overflow Interrupt Enable

When the TOIE1 bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter1 Overflow Interrupt is enabled. The corresponding interrupt (at vector $008) is executed if an overflow in Timer/Counter1 occurs (i.e., when the TOV1 bit is set in the Timer/Counter Interrupt Flag Register [TIFR]).

• Bit 1 – Res: Reserved Bit

Timer/Counter Interrupt Flag Register – TIFR

This bit is a reserved bit in the AT90S8535 and always reads zero.

• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable

When the TOIE0 bit is set (one) and the I-bit in the Status Register is set (one), the Timer/Counter0 Overflow Interrupt is enabled. The corresponding interrupt (at vector $009) is executed if an overflow in Timer/Counter0 occurs (i.e., when the TOV0 bit is set in the Timer/Counter Interrupt Flag Register [TIFR]).

Bit 7 6 5 4 3 2 1 0

$38 ($58) OCF2 TOV2 ICF1 OCF1A OCF1B TOV1 – TOV0 TIF R

Read/Write R/W R/W R/W R/W R/W R/W R R/W

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – OCF2: Output Compare Flag 2

The OCF2 bit is set (one) when compare match occurs between the Timer/Counter2 and the data in OCR2 (Output Compare Register2). OCF2 is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF2 is cleared by writing a logical “1” to the flag. When the I-bit in SREG and OCIE2 (Timer/Counter2 Compare Match Interrupt Enable) and the OCF2 are set (one), the Timer/Counter2 Compare Match Interrupt is executed.

• Bit 6 – TOV2: Timer/Counter2 Overflow Flag

The TOV2 bit is set (one) when an overflow occurs in Timer/Counter2. TOV2 is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, TOV2 is cleared by writing a logical “1” to the flag. When the SREG I-bit and TOIE2 (Timer/Counter2 Overflow Interrupt Enable) and TOV2 are set (one), the Timer/Counter2 Overflow Interrupt is executed. In up/down PWM mode, this bit is set when Timer/Counter1 advances from $0000.

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• Bit 5 – ICF1: Input Capture Flag 1

The ICF1 bit is set (one) to flag an input capture event, indicating that the Timer/Counter1 value has been transferred to the Input Capture Register (ICR1). ICF1 is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, ICF1 is cleared by writing a logical “1” to the flag. When the SREG I-bit and TICIE1 (Timer/Counter1 Input Capture Interrupt Enable) and ICF1 are set (one), the Timer/Counter1 Capture Interrupt is executed.

• Bit 4 – OCF1A: Output Compare Flag 1A

The OCF1A bit is set (one) when compare match occurs between the Timer/Counter1 and the data in OCR1A (Output Compare Register 1A). OCF1A is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF1A is cleared by writing a logical “1” to the flag. When the I-bit in SREG and OCIE1A (Timer/Counter1 Compare Match InterruptA Enable) and the OCF1A are set (one), the Timer/Counter1 Compare A Match Interrupt is executed.

• Bit 3 – OCF1B: Output Compare Flag 1B

The OCF1B bit is set (one) when compare match occurs between the Timer/Counter1 and the data in OCR1B (Output Compare Register 1B). OCF1B is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF1B is cleared by writing a logical “1” to the flag. When the I-bit in SREG and OCIE1B (Timer/Counter1 Compare Match InterruptB Enable) and the OCF1B are set (one), the Timer/Counter1 Compare Match B Interrupt is executed.

• Bit 2 – TOV1: Timer/Counter1 Overflow Flag

The TOV1 is set (one) when an overflow occurs in Timer/Counter1. TOV1 is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, TOV1 is cleared by writing a logical “1” to the flag. When the I-bit in SREG and TOIE1 (Timer/Counter1 Overflow Interrupt Enable) and TOV1 are set (one), the Timer/Counter1 Overflow Interrupt is executed. In up/down PWM mode, this bit is set when Timer/Counter1 advances from $0000.

• Bit 1 – Res: Reserved Bit

This bit is a reserved bit in the AT90S8535 and always reads zero.

• Bit 0 – TOV0: Timer/Counter0 Overflow Flag

The bit TOV0 is set (one) when an overflow occurs in Timer/Counter0. TOV0 is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, TOV0 is cleared by writing a logical “1” to the flag. When the SREG I-bit and TOIE0 (Timer/Counter0 Overflow Interrupt Enable) and TOV0 are set (one), the Timer/Counter0 Overflow Interrupt is executed. In up/down PWM mode, this bit is set when Timer/Counter1 advances from $0000.

External Interrupts The external interrupts are triggered by the INT1 and INT0 pins. Observe that, if

enabled, the interrupts will trigger even if the INT0/INT1 pins are configured as outputs. This feature provides a way of generating a software interrupt. The external interrupts can be triggered by a falling or rising edge or a low level. This is set up as indicated in the specification for the MCU Control Register (MCUCR). When the external interrupt is enabled and is configured as level-triggered, the interrupt will trigger as long as the pin is held low.

The external interrupts are set up as described in the specification for the MCU Control Register (MCUCR).

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AT90S/LS8535

Interrupt Response Time The interrupt execution response for all the enabled AVR interrupts is four clock cycles

minimum. Four clock cycles after the interrupt flag has been set, the program vector address for the actual interrupt handling routine is executed. During this 4-clock-cycle period, the Program Counter (2 bytes) is pushed onto the stack and the Stack Pointer is decremented by 2. The vector is normally a relative jump to the interrupt routine and this jump takes two clock cycles. If an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed before the interrupt is served.

A return from an interrupt handling routine (same as for a subroutine call routine) takes four clock cycles. During these four clock cycles, the Program Counter (2 bytes) is popped back from the stack, the Stack Pointer is incremented by 2 and the I-flag in SREG is set. When the AVR exits from an interrupt, it will always return to the main program and execute one more instruction before any pending interrupt is served.

MCU Control Register – MCUCR

The MCU Control Register contains control bits for general MCU functions.

Bit 76543210

$35 ($55) – SE SM1 SM0 ISC11 ISC10 ISC01 ISC00 MCUCR

Read/Write R R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – Res: Reserved Bit

This bit is a reserved bit in the AT90S8535 and always reads zero.

• Bit 6 – SE: Sleep Enable

The SE bit must be set (one) to make the MCU enter the Sleep Mode when the SLEEP instruction is executed. To avoid the MCU entering the Sleep Mode unless it is the programmer’s purpose, it is recommended to set the Sleep Enable (SE) bit just before the execution of the SLEEP instruction.

• Bits 5, 4 – SM1/SM0: Sleep Mode Select Bits 1 and 0

These bits select between the three available sleep modes as shown in Table 7.

Table 7. Sleep Mode Select

SM1 SM0 Sleep Mode

00Idle

01Reserved

1 0 Power-down

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11Power Save

• Bits 3, 2 – ISC11, ISC10: Interrupt Sense Control 1 Bits 1 and 0

The External Interrupt 1 is activated by the external pin INT1 if the SREG I-flag and the corresponding interrupt mask in the GIMSK is set. The level and edges on the external INT1 pin that activate the interrupt are defined in Table 8.

Table 8. Interrupt 1 Sense Control

ISC11 ISC10 Description

0 0 The low level of INT1 generates an interrupt request.

01Reserved

1 0 The falling edge of INT1 generates an interrupt request.

1 1 The rising edge of INT1 generates an interrupt request.

The value on the INT pin is sampled before detecting edges. If edge interrupt is selected, pulses that last longer than one CPU clock period will generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If low-level interrupt is selected, the low level must be held until the completion of the currently executing instruction to generate an interrupt. If enabled, a level-triggered interrupt will generate an interrupt request as long as the pin is held low.

• Bit 1, 0 – ISC01, ISC00: Interrupt Sense Control 0 Bits 1 and 0

The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corresponding interrupt mask is set. The level and edges on the external INT0 pin that activate the interrupt are defined in Table 9.

Table 9. Interrupt 0 Sense Control

ISC01 ISC00 Description

0 0 The low level of INT0 generates an interrupt request.

01Reserved

1 0 The falling edge of INT0 generates an interrupt request.

1 1 The rising edge of INT0 generates an interrupt request.

Sleep Modes To enter any of the three sleep modes, the SE bit in MCUCR must be set (one) and a

SLEEP instruction must be executed. The SM0 and SM1 bits in the MCUCR register select which sleep mode (Idle, Power-down or Power Save) will be activated by the SLEEP instruction. See Table 7.

If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up, executes the interrupt routine and resumes execution from the instruction following SLEEP. The contents of the register file, SRAM and I/O memory are unaltered. If a reset occurs during Sleep Mode, the MCU wakes up and executes from the Reset vector.

Idle Mode When the SM1/SM0 bits are set to 00, the SLEEP instruction makes the MCU enter the

Idle Mode, stopping the CPU but allowing SPI, UARTs, Analog Comparator, ADC, Timer/Counters, Watchdog and the interrupt system to continue operating. This enables the MCU to wake up from external triggered interrupts as well as internal ones like the Timer Overflow and UART Receive Complete interrupts. If wake-up from the Analog

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AT90S/LS8535

Comparator Interrupt is not required, the Analog Comparator can be powered down by setting the ACD-bit in the Analog Comparator Control and Status Register (ACSR). This will reduce power consumption in Idle Mode. When the MCU wakes up from Idle Mode, the CPU starts program execution immediately.

Power-down Mode When the SM1/SM0 bits are set to 10, the SLEEP instruction makes the MCU enter the

Power-down mode. In this mode, the external oscillator is stopped while the external interrupts and the Watchdog (if enabled) continue operating. Only an external reset, a Watchdog reset (if enabled) or an external level interrupt can wake up the MCU.

Note that when a level-triggered interrupt is used for wake-up from power-down, the low level must be held for a time longer than the reset delay Time-out period t

When waking up from Power-down mode, a delay from the wake-up condition occurs until the wake-up becomes effective. This allows the clock to restart and become stable after having been stopped. The wake-up period is equal to the reset period, as shown in Table 3 on page 22.

If the wake-up condition disappears before the MCU wakes up and starts to execute, e.g., a low-level on is not held long enough, the interrupt causing the wake-up will not be executed.

Power Save Mode When the SM1/SM0 bits are 11, the SLEEP instruction makes the MCU enter the Power

Save Mode. This mode is identical to Power-down, with one exception: If Timer/Counter2 is clocked asynchronously, i.e., the AS2 bit in ASSR is set, Timer/Counter2 will run during sleep. In addition to the power-down wake-up sources, the device can also wake up from either a Timer Overflow or Output Compare event from Timer/Counter2 if the corresponding Timer/Counter2 interrupt enable bits are set in TIMSK and the global interrupt enable bit in SREG is set.

TOUT

When waking up from Power Save Mode by an external interrupt, two instruction cycles are executed before the interrupt flags are updated. When waking up by the asynchronous timer, three instruction cycles are executed before the flags are updated. During these cycles, the processor executes instructions, but the interrupt condition is not readable and the interrupt routine has not started yet.

When waking up from Power Save Mode by an asynchronous timer interrupt, the part will wake up even if global interrupts are disabled. To ensure that the part executes the interrupt routine when waking up, also set the global interrupt enable bit in SREG.

If the asynchronous timer is not clocked asynchronously, Power-down mode is recommended instead of Power Save Mode because the contents of the registers in the asynchronous timer should be considered undefined after wake-up in Power Save Mode, even if AS2 is 0.

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Timer/Counters The AT90S8535 provides three general-purpose Timer/Counters – two 8-bit T/Cs and

one 16-bit T/C. Timer/Counter2 can optionally be asynchronously clocked from an external oscillator. This oscillator is optimized for use with a 32.768 kHz watch crystal, enabling use of Timer/Counter2 as a Real-time Clock (RTC). Timer/Counters 0 and 1 have individual prescaling selection from the same 10-bit prescaling timer. Timer/Counter2 has its own prescaler. These Timer/Counters can either be used as a timer with an internal clock time base or as a counter with an external pin connection that triggers the counting.

Timer/Counter Prescalers

Figure 28. Prescaler for Timer/Counter0 and 1

TCK1

TCK0

For Timer/Counters 0 and 1, the four different prescaled selections are: CK/8, CK/64, CK/256 and CK/1024, where CK is the oscillator clock. For the two Timer/Counters 0 and 1, CK, external source and stop can also be selected as clock sources.

Figure 29. Timer/Counter2 Prescaler

AT90S/LS8535

TOSC1

AS2

CS20 CS21 CS22

PCK2

10-BIT T/C PRESCALER

PCK2/8

TIMER/COUNTER2 CLOCK SOURCE

TCK2

PCK2/32

PCK2/64

PCK2/128

PCK2/256

PCK2/1024

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The clock source for Timer/Counter2 prescaler is named PCK2. PCK2 is by default connected to the main system clock (CK). By setting the AS2 bit in ASSR, Timer/Counter2 prescaler is asynchronously clocked from the PC6(TOSC1) pin. This enables use of Timer/Counter2 as a Real-time Clock (RTC). When AS2 is set, pins PC6(TOSC1) and PC7(TOSC2) are disconnected from Port C. A crystal can then be connected between the PC6(TOSC1) and PC7(TOSC2) pins to serve as an independent clock source for Timer/Counter2. The oscillator is optimized for use with a 32.768 kHz crystal. Applying an external clock source to TOSC1 is not recommended.

8-bit Timer/Counter0 Figure 30 shows the block diagram for Timer/Counter0.

The 8-bit Timer/Counter0 can select clock source from CK, prescaled CK or an external pin. In addition, it can be stopped as described in the specification for the Timer/Counter0 Control Register (TCCR0). The overflow status flag is found in the Timer/Counter Interrupt Flag Register (TIFR). Control signals are found in the Timer/Counter0 Control Register (TCCR0). The interrupt enable/disable settings for Timer/Counter0 are found in the Timer/Counter Interrupt Mask Register (TIMSK).

When Timer/Counter0 is externally clocked, the external signal is synchronized with the oscillator frequency of the CPU. To assure proper sampling of the external clock, the minimum time between two external clock transitions must be at least one internal CPU clock period. The external clock signal is sampled on the rising edge of the internal CPU clock.

AT90S/LS8535

The 8-bit Timer/Counter0 features both a high-resolution and a high-accuracy usage with the lower prescaling opportunities. Similarly, the high prescaling opportunities make the Timer/Counter0 useful for lower speed functions or exact timing functions with infrequent actions.

Figure 30. Timer/Counter0 Block Diagram

T/C0 OVER-

FLOW IRQ

OCIE1A

OCIE1B

TICIE1

TOIE2

TA BUS

8-BIT DA

OCIE2

TIMER INT. MASK

TIMER/COUNTER0

(TCNT0)

TOIE1

TOIE0

TIMER INT. FLAG

ICF1

TOV2

OCF2

OCF1B

T/C CLK SOURCE

OCF1A

TOV1

TOV0

T/C0 CONTROL

CONTROL

LOGIC

CS02

CS01

CS00

1041H–11/01

Timer/Counter0 Control Register – TCCR0

Bit 7 6 5 4 3 210

$33 ($53) –– – – –CS02 CS01 CS00 TCCR0

Read/Write R R R R R R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

• Bits 7..3 – Res: Reserved Bits

These bits are reserved bits in the AT90S8535 and always read zero.

• Bits 2, 1, 0 – CS02, CS01, CS00: Clock Select0, Bits 2, 1 and 0

The Clock Select0 bits 2,1 and 0 define the prescaling source of Timer/Counter0.

Table 10. Clock 0 Prescale Select

CS02 CS01 CS00 Description

0 0 0 Stop, Timer/Counter0 is stopped.

001CK

010CK/8

011CK/64

100CK/256

101CK/1024

1 1 0 External Pin T0, falling edge

Timer Counter 0 – TCNT0

1 1 1 External Pin T0, rising edge

The Stop condition provides a Timer Enable/Disable function. The prescaled CK modes are scaled directly from the CK oscillator clock. If the external pin modes are used, the corresponding setup must be performed in the actual Data Direction Control Register (cleared to zero gives an input pin).

Bit 76543210

$32 ($52) MSB LSB TCNT0

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

The Timer/Counter0 is realized as an up-counter with read and write access. If the Timer/Counter0 is written and a clock source is present, the Timer/Counter0 continues counting in the clock cycle following the write operation.

AT90S/LS8535

1041H–11/01

16-bit Timer/Counter1 Figure 31 shows the block diagram for Timer/Counter1.

Figure 31. Timer/Counter1 Block Diagram

T/C1 OVER-

FLOW IRQ

TOIE1

OCIE1A

OCIE1B

TICIE1

TOIE2

TA BU S

8-BIT DA

OCIE2

TIMER INT. MASK

T/C1 INPUT CAPTURE REGISTER (ICR1)

T/C1 COMPARE

TOIE0

MATCHA IRQ

OCF2

TOV2

TIMER INT. FLAG

ICF1

OCF1B

T/C1 COMPARE

MATCHB IRQ

TOV0

OCF1A

TOV1

OCF1A

CAPTURE TRIGGER

T/C1 INPUT

CAPTURE IRQ

T/C1 CONTROL

COM1B1

COM1A1

COM1A0

COM1B0

AT90S/LS8535

T/C1 CONTROL

CS11

CS12

CS10

PWM11

PWM10

CONTROL

LOGIC

ICNC1

ICES1

CTC1

TIMER/COUNTER1 OUTPUT COMPARE REGISTER A

TIMER/COUNTER1 (TCNT1)

16 BIT COMPARATOR

T/C CLEAR

T/C CLOCK SOURCE

UP/DOWN

TIMER/COUNTER1 OUTPUT COMPARE REGISTER B

16 BIT COMPARATOR

The 16-bit Timer/Counter1 can select clock source from CK, prescaled CK or an external pin. In addition, it can be stopped as described in the specification for the Timer/Counter1 Control Registers (TCCR1A and TCCR1B). The different status flags (Overflow, Compare Match and Capture Event) and control signals are found in the Timer/Counter1 Control Registers (TCCR1A and TCCR1B). The interrupt enable/disable settings for Timer/Counter1 are found in the Timer/Counter Interrupt Mask Register (TIMSK).

When Timer/Counter1 is externally clocked, the external signal is synchronized with the oscillator frequency of the CPU. To assure proper sampling of the external clock, the minimum time between two external clock transitions must be at least one internal CPU clock period. The external clock signal is sampled on the rising edge of the internal CPU clock.

The 16-bit Timer/Counter1 features both a high-resolution and a high-accuracy usage with the lower prescaling opportunities. Similarly, the high prescaling opportunities makes the Timer/Counter1 useful for lower speed functions or exact timing functions with infrequent actions.

1041H–11/01

The Timer/Counter1 supports two Output Compare functions using the Output Compare Register 1A and B (OCR1A and OCR1B) as the data sources to be compared to the Timer/Counter1 contents. The Output Compare functions include optional clearing of

the counter on compareA match and actions on the Output Compare pins on both compare matches.

Timer/Counter1 can also be used as an 8-, 9- or 10-bit Pulse Width Modulator. In this mode the counter and the OCR1A/OCR1B registers serve as a dual glitch-free standalone PWM with centered pulses. Refer to page 40 for a detailed description of this function.

The Input Capture function of Timer/Counter1 provides a capture of the Timer/Counter1 contents to the Input Capture Register (ICR1), triggered by an external event on the Input Capture Pin (ICP). The actual capture event settings are defined by the Timer/Counter1 Control Register (TCCR1B). In addition, the Analog Comparator can be set to trigger the input capture. Refer to “Analog Comparator” on page 66 for details on this. The ICP pin logic is shown in Figure 32.

Figure 32. ICP Pin Schematic Diagram

Timer/Counter1 Control Register A – TCCR1A

If the Noise Canceler function is enabled, the actual trigger condition for the capture event is monitored over four samples and all four must be equal to activate the capture flag. The input pin signal is sampled at XTAL clock frequency.

Bit 7 6 5 4 3 2 1 0

$2F ($4F) COM1A1 COM1A0 COM1B1 COM1B0 ––PWM11 PWM10 TCCR1A

Read/Write R/W R/W R/W R/W R R R/W R/W

Initial Value 0 0 0 0 0 0 0 0

• Bits 7, 6 – COM1A1, COM1A0: Compare Output Mode1A, Bits 1 and 0

The COM1A1 and COM1A0 control bits determine any output pin action following a compare match in Timer/Counter1. Any output pin actions affect pin OC1A (Output CompareA pin 1). This is an alternative function to an I/O port and the corresponding direction control bit must be set (one) to control an output pin. The control configuration is shown in Table 11.

• Bits 5, 4 – COM1B1, COM1B0: Compare Output Mode1B, Bits 1 and 0

The COM1B1 and COM1B0 control bits determine any output pin action following a compare match in Timer/Counter1. Any output pin actions affect pin OC1B (Output CompareB). This is an alternative function to an I/O port and the corresponding direction control bit must be set (one) to control an output pin. The control configuration is given in Table 11.

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AT90S/LS8535

Table 11. Compare 1 Mode Select

COM1X1 COM1X0 Description

0 0 Timer/Counter1 disconnected from output pin OC1X

0 1 Toggle the OC1X output line.

1 0 Clear the OC1X output line (to zero).

1 1 Set the OC1X output line (to one).

Note: X = A or B.

In PWM mode, these bits have a different function. Refer to Table 15 for a detailed description. When changing the COM1X1/COM1X0 bits, Output Compare Interrupt 1 must be disabled by clearing their Interrupt Enable bits in the TIMSK Register. Otherwise an interrupt can occur when the bits are changed.

• Bits 3..2 – Res: Reserved Bits

These bits are reserved bits in the AT90S8535 and always read zero.

• Bits 1..0 – PWM11, PWM10: Pulse Width Modulator Select Bits

These bits select PWM operation of Timer/Counter1 as specified in Table 12. This mode is described on page 40.

Table 12. PWM Mode Select

Timer/Counter1 Control Register B – TCCR1B

PWM11 PWM10 Description

0 0 PWM operation of Timer/Counter1 is disabled

0 1 Timer/Counter1 is an 8-bit PWM

1 0 Timer/Counter1 is a 9-bit PWM

1 1 Timer/Counter1 is a 10-bit PWM

Bit 76543210

$2E ($4E) ICNC1 ICES1 ––CTC1 CS12 CS11 CS10 TCCR1B

Read/Write R/W R/W R R R/W R/W R/W R/W

Initial Value0000 0000

• Bit 7 – ICNC1: Input Capture1 Noise Canceler (4 CKs)

When the ICNC1 bit is cleared (zero), the Input Capture Trigger Noise Canceler function is disabled. The input capture is triggered at the first rising/falling edge sampled on the ICP (input capture pin) as specified. When the ICNC1 bit is set (one), four successive samples are measured on the ICP (input capture pin), and all samples must be high/low according to the input capture trigger specification in the ICES1 bit. The actual sampling frequency is XTAL clock frequency.

• Bit 6 – ICES1: Input Capture1 Edge Select

While the ICES1 bit is cleared (zero), the Timer/Counter1 contents are transferred to the Input Capture Register (ICR1) on the falling edge of the input capture pin (ICP). While the ICES1 bit is set (one), the Timer/Counter1 contents are transferred to the Input Capture Register (ICR1) on the rising edge of the input capture pin (ICP).

• Bits 5, 4 – Res: Reserved Bits

1041H–11/01

These bits are reserved bits in the AT90S8535 and always read zero.

• Bit 3 – CTC1: Clear Timer/Counter1 on Compare Match

When the CTC1 control bit is set (one), the Timer/Counter1 is reset to $0000 in the clock cycle after a compareA match. If the CTC1 control bit is cleared, Timer/Counter1 continues counting and is unaffected by a compare match. Since the compare match is detected in the CPU clock cycle following the match, this function will behave differently when a prescaling higher than 1 is used for the timer. When a prescaling of 1 is used and the compareA register is set to C, the timer will count as follows if CTC1 is set:

... | C-2 | C-1 | C | 0 | 1 |...

When the prescaler is set to divide by 8, the timer will count like this:

... | C-2, C-2, C-2, C-2, C-2, C-2, C-2, C-2 | C-1, C-1, C-1, C-1, C-1, C-1, C-1, C-1 | C, 0, 0, 0, 0, 0, 0, 0 |1,1,1,1,1,1,1,1|...

In PWM mode, this bit has no effect.

• Bits 2, 1, 0 – CS12, CS11, CS10: Clock Select1, Bits 2, 1 and 0

The Clock Select1 bits 2, 1 and 0 define the prescaling source of Timer/Counter1.

Table 13. Clock 1 Prescale Select

CS12 CS11 CS10 Description

0 0 0 Stop, the Timer/Counter1 is stopped.

001CK

010CK/8

011CK/64

Timer/Counter1 – TCNT1H AND TCNT1L

100CK/256

1 0 1 CK/1024

1 1 0 External Pin T1, falling edge

1 1 1 External Pin T1, rising edge

The Stop condition provides a Timer Enable/Disable function. The CK down divided modes are scaled directly from the CK oscillator clock. If the external pin modes are used, the corresponding setup must be performed in the actual Direction Control Register (cleared to zero gives an input pin).

Bit 151413121110 9 8

$2D ($4D) MSB TCNT1H

$2C ($4C) LSB TCNT1L

76543210

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

00000000

This 16-bit register contains the prescaled value of the 16-bit Timer/Counter1. To ensure that both the high and low bytes are read and written simultaneously when the CPU accesses these registers, the access is performed using an 8-bit temporary register (TEMP). This temporary register is also used when accessing OCR1A, OCR1B and ICR1. If the main program and also interrupt routines perform access to registers using

AT90S/LS8535

1041H–11/01

Timer/Counter1 Output Compare Register – OCR1AH AND OCR1AL

AT90S/LS8535

TEMP, interrupts must be disabled during access from the main program (and from interrupt routines if interrupts are allowed from within interrupt routines).

• TCNT1 Timer/Counter1 Write:

When the CPU writes to the high byte TCNT1H, the written data is placed in the TEMP register. Next, when the CPU writes the low byte TCNT1L, this byte of data is combined with the byte data in the TEMP register, and all 16 bits are written to the TCNT1 Timer/Counter1 register simultaneously. Consequently, the high byte TCNT1H must be accessed first for a full 16-bit register write operation.

• TCNT1 Timer/Counter1 Read:

When the CPU reads the low byte TCNT1L, the data of the low byte TCNT1L is sent to the CPU and the data of the high byte TCNT1H is placed in the TEMP register. When the CPU reads the data in the high byte TCNT1H, the CPU receives the data in the TEMP register. Consequently, the low byte TCNT1L must be accessed first for a full 16-bit register read operation.

The Timer/Counter1 is realized as an up or up/down (in PWM mode) counter with read and write access. If Timer/Counter1 is written to and a clock source is selected, the Timer/Counter1 continues counting in the timer clock cycle after it is preset with the written value.

Bit 151413121110 9 8

$2B ($4B) MSB OCR1AH

$2A ($4A) LSB OCR1AL

76543210

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

00000000

Timer/Counter1 Output Compare Register – OCR1BH AND OCR1BL

Bit 151413121110 9 8

$29 ($49) MSB OCR1BH

$28 ($48) LSB OCR1BL

76543210

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

00000000

The output compare registers are 16-bit read/write registers.

The Timer/Counter1 Output Compare registers contain the data to be continuously compared with Timer/Counter1. Actions on compare matches are specified in the Timer/Counter1 Control and Status registers. A compare match only occurs if Timer/Counter1 counts to the OCR value. A software write that sets TCNT1 and OCR1A or OCR1B to the same value does not generate a compare match.

A compare match will set the compare interrupt flag in the CPU clock cycle following the compare event.

Since the Output Compare Registers (OCR1A and OCR1B) are 16-bit registers, a temporary register (TEMP) is used when OCR1A/B are written to ensure that both bytes are updated simultaneously. When the CPU writes the high byte, OCR1AH or OCR1BH, the data is temporarily stored in the TEMP register. When the CPU writes the low byte,

1041H–11/01

Timer/Counter1 Input Capture Register – ICR1H AND ICR1L

OCR1AL or OCR1BL, the TEMP register is simultaneously written to OCR1AH or OCR1BH. Consequently, the high byte OCR1AH or OCR1BH must be written first for a full 16-bit register write operation.

The TEMP register is also used when accessing TCNT1 and ICR1. If the main program and interrupt routines perform access to registers using TEMP, interrupts must be disabled during access from the main program.

Bit 151413121110 9 8

$27 ($47) MSB ICR1H

$26 ($46) LSB ICR1L

76543210

Read/WriteRRRRRRRR

RRRRRRRR

Initial Value00000000

00000000

The Input Capture Register is a 16-bit read-only register.

When the rising or falling edge (according to the input capture edge setting [ICES1]) of the signal at the input capture pin (ICP) is detected, the current value of the Timer/Counter1 is transferred to the Input Capture Register (ICR1). At the same time, the input capture flag (ICF1) is set (one).

Since the Input Capture Register (ICR1) is a 16-bit register, a temporary register (TEMP) is used when ICR1 is read to ensure that both bytes are read simultaneously. When the CPU reads the low byte ICR1L, the data is sent to the CPU and the data of the high byte ICR1H is placed in the TEMP register. When the CPU reads the data in the high byte ICR1H, the CPU receives the data in the TEMP register. Consequently, the low-byte ICR1L must be accessed first for a full 16-bit register read operation.

The TEMP register is also used when accessing TCNT1, OCR1A and OCR1B. If the main program and interrupt routines perform access to registers using TEMP, interrupts must be disabled during access from the main program.

Timer/Counter1 In PWM Mode When the PWM mode is selected, Timer/Counter1, the Output Compare Register1A

(OCR1A) and the Output Compare Register1B (OCR1B) form a dual 8-, 9- or 10-bit, free-running, glitch-free and phase-correct PWM with outputs on the PD5(OC1A) and PD4(OC1B) pins. Timer/Counter1 acts as an up/down counter, counting up from $0000 to TOP (see Table 14), where it turns and counts down again to zero before the cycle is repeated. When the counter value matches the contents of the 10 least significant bits of OCR1A or OCR1B, the PD5(OC1A)/PD4(OC1B) pins are set or cleared according to the settings of the COM1A1/COM1A0 or COM1B1/COM1B0 bits in the Timer/Counter1 Control Register (TCCR1A). Refer to Table 15 for details.

Table 14. Timer TOP Values and PWM Frequency

PWM Resolution Timer TOP value Frequency

8-bit $00FF (255) f

9-bit $01FF (511) f

10-bit $03FF(1023) f

TCK1

/510

/1022

/2046

Note that if the Compare Register contains the TOP value and the prescaler is not in use (CS12..CS10 = 001), the PWM output will not produce any pulse at all, because the

AT90S/LS8535

1041H–11/01

AT90S/LS8535

up-counting and down-counting values are reached simultaneously. When the prescaler is in use (CS12..CS10 reaches TOP value, but the down-counting compare match is not interpreted to be reached before the next time the counter reaches the TOP value, making a one-period PWM pulse.

Table 15. Compare1 Mode Select in PWM Mode

COM1X1 COM1X0 Effect on OCX1

0 0 Not connected

0 1 Not connected

≠ 001 or 000), the PWM output goes active when the counter

Note: X = A or B

Cleared on compare match, up-counting. Set on compare match, down-counting (non-inverted PWM).

Cleared on compare match, down-counting. Set on compare match, up-counting (inverted PWM).

Note that in the PWM mode, the 10 least significant OCR1A/OCR1B bits, when written, are transferred to a temporary location. They are latched when Timer/Counter1 reaches the value TOP. This prevents the occurrence of odd-length PWM pulses (glitches) in the event of an unsynchronized OCR1A/OCR1B write. See Figure 33 for an example.

Figure 33. Effects of Unsynchronized OCR1 Latching

Compare V

Synchronized OCR1X Latch

Compare Value changes

Unsynchronized OCR1X Latch

Note: X = A or B

alue changes

Glitch

Counter

Compare V

PWM

Counter Compare Value

PWM Output OC1X

alue

Output OC1X

Value

1041H–11/01

During the time between the write and the latch operations, a read from OCR1A or OCR1B will read the contents of the temporary location. This means that the most recently written value always will read out of OCR1A/B.

When the OCR1A/OCR1B contains $0000 or TOP, the output OC1A/OC1B is updated to low or high on the next compare match according to the settings of COM1A1/COM1A0 or COM1B1/COM1B0. This is shown in Table 16.

Table 16. PWM Outputs OCR1X = $0000 or TOP

COM1X1 COM1X0 OCR1X Output OC1X

1 0 $0000 L

Table 16. PWM Outputs OCR1X = $0000 or TOP

COM1X1 COM1X0 OCR1X Output OC1X

10TOP H

1 1 $0000 H

11TOP L

Note: X = A

In PWM mode, the Timer Overflow Flag1 (TOV1) is set when the counter advances from $0000. Timer Overflow Interrupt1 operates exactly as in normal Timer/Counter mode, i.e., it is executed when TOV1 is set, provided that Timer Overflow Interrupt1 and global interrupts are enabled. This also applies to the Timer Output Compare1 flags and interrupts.

8-bit Timer/Counter2 Figure 34 shows the block diagram for Timer/Counter2.

Figure 34. Timer/Counter2 Block Diagram

T/C2 OVER-

FLOW IRQ

8-BIT DATA BUS

8-BIT ASYNCH T/C2 DATA BUS

T/C2 COMPARE

MATCH IRQ

OCIE1A

OCIE1B

TICIE1

TOIE2

OCIE2

TIMER INT. MASK

TIMER/COUNTER2

(TCNT2)

8-BIT COMPARATOR

OUTPUT COMPARE REGISTER2 (OCR2)

TOIE1

TOIE0

PCK2

TOV2

OCF2

TIMER INT. FLAG

ICF1

TOV2

OCF2

T/C CLEAR

T/C CLK SOURCE

UP/DOWN

OCF1B

OCF1A

SYNCH UNIT

TOV1

TOV0

T/C2 CONTROL

PWM2

COM20

COM21

CONTROL

LOGIC

ASYNCH. STATUS

CTC2

AS2

CS22

TC2UB

CS20

CS21

ICR2UB

OCR2UB

TOSC1

The 8-bit Timer/Counter2 can select clock source from PCK2 or prescaled PCK2. It can also be stopped as described in the specification for the Timer/Counter Control Register (TCCR2).

The different status flags (Overflow and Compare Match) are found in the Timer/Counter Interrupt Flag Register (TIFR). Control signals are found in the

AT90S/LS8535

1041H–11/01

Timer/Counter2 Control Register – TCCR2

AT90S/LS8535

Timer/Counter Control Register (TCCR2). The interrupt enable/disable settings are found in the Timer/Counter Interrupt Mask Register (TIMSK).

This module features a high-resolution and a high-accuracy usage with the lower prescaling opportunities. Similarly, the high prescaling opportunities make this unit useful for lower speed functions or exact timing functions with infrequent actions.

The Timer/Counter supports an Output Compare function using the Output Compare Register (OCR2) as the data source to be compared to the Timer/Counter contents.The Output Compare function includes optional clearing of the counter on compare match and action on the Output Compare Pin, PD7(OC2), on compare match. Writing to PORTD7 does not set the OC2 value to a predetermined value.

Timer/Counter2 can also be used as an 8-bit Pulse Width Modulator. In this mode, Timer/Counter2 and the Output Compare Register serve as a glitch-free, stand-alone PWM with centered pulses. Refer to page 45 for a detailed description of this function.

Bit 76543210

$25 ($45) – PWM2 COM21 COM20 CTC2 CS22 CS21 CS20 TCCR2

Read/Write R R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – Res: Reserved Bit

This bit is a reserved bit in the AT90S8535 and always reads as zero.

• Bit 6 – PWM2: Pulse Width Modulator Enable

When set (one), this bit enables PWM mode for Timer/Counter2. This mode is described on page 45.

• Bits 5, 4 – COM21, COM20: Compare Output Mode, Bits 1 and 0

The COM21 and COM20 control bits determine any output pin action following a compare match in Timer/Counter2. Output pin actions affect pin PD7(OC2). This is an alternative function to an I/O port and the corresponding direction control bit must be set (one) to control an output pin. The control configuration is shown in Table 17.

Table 17. Compare Mode Select

COM21 COM20 Description

0 0 Timer/Counter disconnected from output pin OC2

0 1 Toggle the OC2 output line.

1 0 Clear the OC2 output line (to zero).

1 1 Set the OC2 output line (to one).

Note: In PWM mode, these bits have a different function. Refer to Table 19 for a detailed

description.

• Bit 3 – CTC2: Clear Timer/Counter on Compare Match

1041H–11/01

When the CTC2 control bit is set (one), Timer/Counter2 is reset to $00 in the CPU clock cycle after a compare match. If the control bit is cleared, Timer/Counter2 continues counting and is unaffected by a compare match. Since the compare match is detected in the CPU clock cycle following the match, this function will behave differently when a prescaling higher than 1 is used for the timer. When a prescaling of 1 is used and the compare2 register is set to C, the timer will count as follows if CTC2 is set:

... | C-2 | C-1 | C | 0 | 1 |...

When the prescaler is set to divide by 8, the timer will count like this:

... | C-2, C-2, C-2, C-2, C-2, C-2, C-2, C-2 | C-1, C-1, C-1, C-1, C-1, C-1, C-1, C-1 | C, 0, 0, 0, 0, 0, 0, 0 | 1, 1, 1,...

In PWM mode, this bit has no effect.

• Bits 2, 1, 0 – CS22, CS21, CS20: Clock Select Bits 2, 1 and 0

The Clock Select bits 2,1 and 0 define the prescaling source of Timer/Counter2.

Table 18. Timer/Counter2 Prescale Select

CS22 CS21 CS20 Description

0 0 0 Timer/Counter2 is stopped.

001PCK2

010PCK2/ 8

011PCK2/ 32

100PCK2/ 64

1 0 1 PCK2/128

1 1 0 PCK2/256

1 1 1 PCK2/1024

The Stop condition provides a Timer Enable/Disable function. The prescaled CK modes are scaled directly from the CK oscillator clock.

Timer/Counter2 – TCNT2

Timer/Counter2 Output Compare Register – OCR2

Bit 76543210

$24 ($44) MSB LSB TCNT2

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

This 8-bit register contains the value of Timer/Counter2.

Timer/Counter2 is realized as an up or up/down (in PWM mode) counter with read and write access. If the Timer/Counter2 is written to and a clock source is selected, it continues counting in the timer clock cycle following the write operation.

Bit 76543210

$23 ($43) MSB LSB OCR2

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value00000000

The Output Compare Register is an 8-bit read/write register.

The Timer/Counter Output Compare Register contains the data to be continuously compared with Timer/Counter2. Actions on compare matches are specified in TCCR2. A compare match only occurs if Timer/Counter2 counts to the OCR2 value. A software write that sets TCNT2 and OCR2 to the same value does not generate a compare match.

A compare match will set the compare interrupt flag in the CPU clock cycle following the compare event.

AT90S/LS8535

1041H–11/01

AT90S/LS8535

Timer/Counter2 in PWM Mode When the PWM mode is selected, Timer/Counter2 and the Output Compare Register

(OCR2) form an 8-bit, free-running, glitch-free and phase correct PWM with outputs on the PD7(OC2) pin. Timer/Counter2 acts as an up/down counter, counting up from $00 to $FF, where it turns and counts down again to zero before the cycle is repeated. When the counter value matches the contents of the Output Compare Register, the PD7(OC2) pin is set or cleared according to the settings of the COM21/COM20 bits in the Timer/Counter2 Control Register (TCCR2). Refer to Table 19 for details.

Table 19. Compare Mode Select in PWM Mode

COM21 COM20 Effect on Compare Pin

0 0 Not connected

0 1 Not connected

1 0 Cleared on compare match, up-counting. Set on compare match, down-

counting (non-inverted PWM).

1 1 Cleared on compare match, down-counting time-out. Set on compare

match, up-counting (inverted PWM).

Note that in PWM mode, the Output Compare Register is transferred to a temporary location when written. The value is latched when the Timer/Counter reaches $FF. This prevents the occurrence of odd-length PWM pulses (glitches) in the event of an unsynchronized OCR2 write. See Figure 35 for an example.

Figure 35. Effects of Unsynchronized OCR Latching

Compare Value changes

Synchronized OCR Latch

Compare Value changes

Unsynchronized OCR Latch

Glitch

Counter Value Compare Valu

PWM Output

Counter Value Compare Valu

PWM Output

During the time between the write and the latch operation, a read from OCR2 will read the contents of the temporary location. This means that the most recently written value always will read out of OCR2.

When the OCR register (not the temporary register) is updated to $00 or $FF, the PWM output changes to low or high immediately according to the settings of COM21/COM20. This is shown in Table 20.

Table 20. PWM Outputs OCR2 = $00 or $FF

1041H–11/01

COM21 COM20 OCR2 Output PWM2

10$00 L

Asynchronous Status Register – ASSR

Table 20. PWM Outputs OCR2 = $00 or $FF

COM21 COM20 OCR2 Output PWM2

10$FF H

11$00 H

11$FF L

In PWM mode, the Timer Overflow Flag (TOV2) is set when the counter advances from $00. Timer Overflow Interrupt2 operates exactly as in normal Timer/Counter mode, i.e., it is executed when TOV2 is set, provided that Timer Overflow Interrupt and global interrupts are enabled. This also applies to the Timer Output Compare flag and interrupt.

The frequency of the PWM will be Timer Clock Frequency divided by 510.

Bit 76543 2 1 0

$22 ($22) ––––AS2 TCN2UB OCR2UB TCR2UB ASSR

Read/Write R R R R R/W R R R

Initial Value 0 0 0 0 0 0 0 0

• Bit 7..4 – Res: Reserved Bits

These bits are reserved bits in the AT90S8535 and always read as zero.

• Bit 3 – AS2: Asynchronous Timer/Counter2

When AS2 is set (one), Timer/Counter2 is clocked from the TOSC1 pin. Pins PC6 and PC7 become connected to a crystal oscillator and cannot be used as general I/O pins. When cleared (zero), Timer/Counter2 is clocked from the internal system clock, CK. When the value of this bit is changed, the contents of TCNT2, OCR2 and TCCR2 might get corrupted.

• Bit 2 – TCN2UB: Timer/Counter2 Update Busy

When Timer/Counter2 operates asynchronously and TCNT2 is written, this bit becomes set (one). When TCNT2 has been updated from the temporary storage register, this bit is cleared (zero) by hardware. A logical “0” in this bit indicates that TCNT2 is ready to be updated with a new value.

• Bit 1 – OCR2UB: Output Compare Register2 Update Busy

When Timer/Counter2 operates asynchronously and OCR2 is written, this bit becomes set (one). When OCR2 has been updated from the temporary storage register, this bit is cleared (zero) by hardware. A logical “0” in this bit indicates that OCR2 is ready to be updated with a new value.

• Bit 0 – TCR2UB: Timer/Counter Control Register2 Update Busy

When Timer/Counter2 operates asynchronously and TCCR2 is written, this bit becomes set (one). When TCCR2 has been updated from the temporary storage register, this bit is cleared (zero) by hardware. A logical “0” in this bit indicates that TCCR2 is ready to be updated with a new value.

If a write is performed to any of the three Timer/Counter2 registers while its Update Busy flag is set (one), the updated value might get corrupted and cause an unintentional interrupt to occur.

The mechanisms for reading TCNT2, OCR2 and TCCR2 are different. When reading TCNT2, the actual timer value is read. When reading OCR2 or TCCR2, the value in the temporary storage register is read.

AT90S/LS8535

1041H–11/01

AT90S/LS8535

Asynchronous Operation of Timer/Counter2

When Timer/Counter2 operates asynchronously, some considerations must be taken.

• Warning: When switching between asynchronous and synchronous clocking of

Timer/Counter2, the timer registers TCNT2, OCR2 and TCCR2 might get corrupted. A safe procedure for switching clock source is:

1. Disable the Timer/Counter2 interrupts OCIE2 and TOIE2.

2. Select clock source by setting AS2 as appropriate.

3. Write new values to TCNT2, OCR2 and TCCR2.

4. To switch to asynchronous operation: Wait for TCN2UB, OCR2UB and TCR2UB.

5. Clear the Timer/Counter2 interrupt flags.

6. Clear the TOV2 and OCF2 flags in TIFR.

7. Enable interrupts, if needed.

• When writing to one of the registers TCNT2, OCR2 or TCCR2, the value is transferred to a temporary register and latched after two positive edges on TOSC1. The user should not write a new value before the contents of the temporary register have been transferred to their destination. Each of the three mentioned registers have their individual temporary register. For example, writing to TCNT2 does not disturb an OCR2 write in progress. To detect that a transfer to the destination register has taken place, an Asynchronous Status Register (ASSR) has been implemented.

• When entering a Power Save Mode after having written to TCNT2, OCR2 or TCCR2, the user must wait until the written register has been updated if Timer/Counter2 is used to wake up the device. Otherwise, the MCU will go to sleep before the changes have had any effect. This is extremely important if the Output Compare2 interrupt is used to wake up the device; Output Compare is disabled during write to OCR2 or TCNT2. If the write cycle is not finished (i.e., the user goes to sleep before the OCR2UB bit returns to zero), the device will never get a compare match and the MCU will not wake up.

• If Timer/Counter2 is used to wake up the device from Power Save Mode, precautions must be taken if the user wants to re-enter Power Save Mode: The interrupt logic needs one TOSC1 cycle to be reset. If the time between wake up and re-entering Power Save Mode is less than one TOSC1 cycle, the interrupt will not occur and the device will fail to wake up. If the user is in doubt whether the time before re-entering Power Save is sufficient, the following algorithm can be used to ensure that one TOSC1 cycle has elapsed:

1. Write a value to TCCR2, TCNT2 or OCR2.

2. Wait until the corresponding Update Busy flag in ASSR returns to zero.

3. Enter Power Save Mode.

• When the asynchronous operation is selected, the 32 kHz oscillator for Timer/Counter2 is always running, except in Power-down mode. After a power-up reset or wake-up from power-down, the user should be aware of the fact that this oscillator might take as long as one second to stabilize. The user is advised to wait for at least one second before using Timer/Counter2 after power-up or wake-up from power-down. The content of all Timer/Counter2 registers must be considered lost after a wake-up from power-down due to the unstable clock signal upon start-up, regardless of whether the oscillator is in use or a clock signal is applied to the TOSC pin.

• Description of wake-up from Power Save Mode when the timer is clocked asynchronously: When the interrupt condition is met, the wake-up process is started on the following cycle of the timer clock, that is, the timer is always advanced by at

1041H–11/01

least one before the processor can read the counter value. After wake-up, the MCU is halted for four cycles, it executes the interrupt routine, and resumes execution from the instruction following SLEEP.

• During asynchronous operation, the synchronization of the interrupt flags for the asynchronous timer takes three processor cycles plus one timer cycle. The timer is therefore advanced by at least 1 before the processor can read the timer value causing the setting of the interrupt flag. The output compare pin is changed on the timer clock and is not synchronized to the processor clock.

AT90S/LS8535

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AT90S/LS8535

Watchdog Timer The Watchdog Timer is clocked from a separate On-chip oscillator. By controlling the

Watchdog Timer prescaler, the Watchdog reset interval can be adjusted as shown in Table 21. See characterization data for typical values at other V (Watchdog Reset) instruction resets the Watchdog Timer. Eight different clock cycle periods can be selected to determine the reset period. If the reset period expires without another Watchdog reset, the AT90S8535 resets and executes from the reset vector. For timing details on the Watchdog reset, refer to page 22.

To prevent unintentional disabling of the Watchdog, a special turn-off sequence must be followed when the Watchdog is disabled. Refer to the description of the Watchdog Timer Control Register for details.

Figure 36. Watchdog Timer

Oscillator

levels. The WDR

Watchdog Timer Control Register – WDTCR

1 MHz at V

350 kHz at V

Bit 76543210

$21 ($41) –––WDTOE WDE WDP2 WDP1 WDP0 WDTCR

Read/Write R R R R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

= 5V

= 3V

• Bits 7..5 – Res: Reserved Bits

These bits are reserved bits in the AT90S8535 and will always read as zero.

1041H–11/01

• Bit 4 – WDTOE: Watchdog Turn-off Enable

This bit must be set (one) when the WDE bit is cleared. Otherwise, the Watchdog will not be disabled. Once set, hardware will clear this bit to zero after four clock cycles. Refer to the description of the WDE bit for a Watchdog disable procedure.

• Bit 3 – WDE: Watchdog Enable

When the WDE is set (one) the Watchdog Timer is enabled and if the WDE is cleared (zero) the Watchdog Timer function is disabled. WDE can only be cleared if the WDTOE bit is set (one). To disable an enabled Watchdog Timer, the following procedure must be followed:

1. In the same operation, write a logical “1” to WDTOE and WDE. A logical “1” must be written to WDE even though it is set to “1” before the disable operation starts.

2. Within the next four clock cycles, write a logical “0” to WDE. This disables the Watchdog.

• Bits 2..0 – WDP2, WDP1, WDP0: Watchdog Timer Prescaler 2, 1 and 0

The WDP2, WDP1 and WDP0 bits determine the Watchdog Timer prescaling when the Watchdog Timer is enabled. The different prescaling values and their corresponding time-out periods are shown in Table 21.

Table 21. Watchdog Timer Prescale Select

Number of WDT

WDP2 WDP1 WDP0

0 0 0 16K cycles 47 ms 15 ms

0 0 1 32K cycles 94 ms 30 ms

0 1 0 64K cycles 0.19 s 60 ms

0 1 1 128K cycles 0.38 s 0.12 s

1 0 0 256K cycles 0.75 s 0.24 s

1 0 1 512K cycles 1.5 s 0.49 s

1 1 0 1,024K cycles 3.0 s 0.97 s

1 1 1 2,048K cycles 6.0 s 1.9 s

Note: The frequency of the Watchdog oscillator is voltage-dependent as shown in the Electrical

Characteristics section. The WDR (Watchdog Reset) instruction should always be executed before the Watchdog Timer is enabled. This ensures that the reset period will be in accordance with the Watchdog Timer prescale settings. If the Watchdog Timer is enabled without reset, the Watchdog Timer may not start to count from zero. To avoid unintentional MCU resets, the Watchdog Timer should be disabled or reset before changing the Watchdog Timer Prescale Select.

Oscillator Cycles

Typical Time-out at VCC = 3.0V

Typical Time-out at VCC = 5.0V

AT90S/LS8535

1041H–11/01

AT90S/LS8535

EEPROM Read/Write Access

EEPROM Address Register – EEARH and EEARL

The EEPROM access registers are accessible in the I/O space.

The write access time is in the range of 2.5 - 4 ms, depending on the V

voltages. A

self-timing function lets the user software detect when the next byte can be written. A special EEPROM Ready interrupt can be set to trigger when the EEPROM is ready to accept new data.

In order to prevent unintentional EEPROM writes, a specific write procedure must be followed. Refer to the description of the EEPROM Control Register for details on this.

When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next instruction is executed.

Bit 151413121110 9 8

$1F ($3F) –––––––EEAR8 EEARH

$1E ($3E) EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL

76543210

Read/WriteRRRRRRRR/W

R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 X

XXXXXXXX

The EEPROM address registers (EEARH and EEARL) specify the EEPROM address in the 512-byte EEPROM space. The EEPROM data bytes are addressed linearly between 0 and 511.

EEPROM Data Register – EEDR

EEPROM Control Register – EECR

Bit 76543210

$1D ($3D) MSB LSB EEDR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

• Bits 7..0 – EEDR7.0: EEPROM Data

For the EEPROM write operation, the EEDR register contains the data to be written to the EEPROM in the address given by the EEAR register. For the EEPROM read operation, the EEDR contains the data read out from the EEPROM at the address given by EEAR.

Bit 76543 2 10

$1C ($3C) ––––EERIE EEMWE EEWE EERE EECR

Read/Write R R R R R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

• Bit 7..4 – Res: Reserved Bits

These bits are reserved bits in the AT90S8535 and will always read as zero.

• Bit 3 – EERIE: EEPROM Ready Interrupt Enable

When the I-bit in SREG and EERIE are set (one), the EEPROM Ready Interrupt is enabled. When cleared (zero), the interrupt is disabled. The EEPROM Ready Interrupt generates a constant interrupt when EEWE is cleared (zero).

1041H–11/01

• Bit 2 – EEMWE: EEPROM Master Write Enable

The EEMWE bit determines whether setting EEWE to “1” causes the EEPROM to be written. When EEMWE is set (one), setting EEWE will write data to the EEPROM at the selected address. If EEMWE is zero, setting EEWE will have no effect. When EEMWE has been set (one) by software, hardware clears the bit to zero after four clock cycles. See the description of the EEWE bit for a EEPROM write procedure.

• Bit 1 – EEWE: EEPROM Write Enable

The EEPROM Write Enable signal (EEWE) is the write strobe to the EEPROM. When address and data are correctly set up, the EEWE bit must be set to write the value into the EEPROM. The EEMWE bit must be set when the logical “1” is written to EEWE, otherwise no EEPROM write takes place. The following procedure should be followed when writing the EEPROM (the order of steps 2 and 3 is unessential):

1. Wait until EEWE becomes zero.

2. Write new EEPROM address to EEARL and EEARH (optional).

3. Write new EEPROM data to EEDR (optional).

4. Write a logical “1” to the EEMWE bit in EECR (to be able to write a logical “1” to the EEMWE bit, the EEWE bit must be written to “0” in the same cycle).

5. Within four clock cycles after setting EEMWE, write a logical “1” to EEWE.

Caution: An interrupt between step 4 and step 5 will make the write cycle fail, since the EEPROM Master Write Enable will time-out. If an interrupt routine accessing the EEPROM is interrupting another EEPROM access, the EEAR and EEDR registers will be modified, causing the interrupted EEPROM access to fail. It is recommended to have the global interrupt flag cleared during the four last steps to avoid these problems.

When the write access time (typically 2.5 ms at V elapsed, the EEWE bit is cleared (zero) by hardware. The user software can poll this bit and wait for a zero before writing the next byte. When EEWE has been set, the CPU is halted for two clock cycles before the next instruction is executed.

• Bit 0 – EERE: EEPROM Read Enable

The EEPROM Read Enable signal (EERE) is the read strobe to the EEPROM. When the correct address is set up in the EEAR register, the EERE bit must be set. When the EERE bit is cleared (zero) by hardware, requested data is found in the EEDR register. The EEPROM read access takes one instruction and there is no need to poll the EERE bit. When EERE has been set, the CPU is halted for four clock cycles before the next instruction is executed.

The user should poll the EEWE bit before starting the read operation. If a write operation is in progress when new data or address is written to the EEPROM I/O registers, the write operation will be interrupted and the result is undefined.

= 5V or 4 ms at VCC = 2.7V) has

AT90S/LS8535

1041H–11/01

AT90S/LS8535

Prevent EEPROM Corruption

During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is too low for the CPU and the EEPROM to operate properly. These issues are the same as for board level systems using the EEPROM and the same design solutions should be applied.

An EEPROM data corruption can be caused by two situations when the voltage is too low. First, a regular write sequence to the EEPROM requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions is too low.

EEPROM data corruption can easily be avoided by following these design recommendations (one is sufficient):

1. Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This is best done by an external low V referred to as a Brown-out Detector (BOD). Please refer to application note AVR 180 for design considerations regarding power-on reset and low-voltage detection.

2. Keep the AVR core in Power-down Sleep Mode during periods of low V will prevent the CPU from attempting to decode and execute instructions, effectively protecting the EEPROM registers from unintentional writes.

3. Store constants in Flash memory if the ability to change memory contents from software is not required. Flash memory cannot be updated by the CPU and will not be subject to corruption.

Reset Protection circuit, often

. This

1041H–11/01

Serial Peripheral Interface – SPI

The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer between the AT90S8535 and peripheral devices or between several AVR devices. The AT90S8535 SPI features include the following:

Full-duplex, 3-wire Synchronous Data Transfer

•

• Master or Slave Operation

• LSB First or MSB First Data Transfer

• Four Programmable Bit Rates

• End-of-transmission Interrupt Flag

• Write Collision Flag Protection

• Wake-up from Idle Mode

Figure 37. SPI Block Diagram

The interconnection between master and slave CPUs with SPI is shown in Figure 38. The PB7(SCK) pin is the clock output in the Master Mode and is the clock input in the Slave Mode. Writing to the SPI Data Register of the master CPU starts the SPI clock generator and the data written shifts out of the PB5(MOSI) pin and into the PB5(MOSI) pin of the slave CPU. After shifting one byte, the SPI clock generator stops, setting the end-of-transmission flag (SPIF). If the SPI interrupt enable bit (SPIE) in the SPCR register is set, an interrupt is requested. The Slave Select input, PB4(SS), is set low to select an individual slave SPI device. The two shift registers in the master and the slave can be considered as one distributed 16-bit circular shift register. This is shown in Figure 38. When data is shifted from the master to the slave, data is also shifted in the opposite direction, simultaneously. During one shift cycle, data in the master and the slave is interchanged.

AT90S/LS8535

1041H–11/01

Figure 38. SPI Master-slave Interconnection

AT90S/LS8535

MSB MASTER LSB

8 BIT SHIFT REGISTER

SPI

CLOCK GENERATOR

MISO

MOSI

SCK

MISO

MOSI

SCK

MSB MASTER LSB

8 BIT SHIFT REGISTER

The system is single-buffered in the transmit direction and double-buffered in the receive direction. This means that bytes to be transmitted cannot be written to the SPI Data Register before the entire shift cycle is completed. When receiving data, however, a received byte must be read from the SPI Data Register before the next byte has been completely shifted in. Otherwise, the first byte is lost.

When the SPI is enabled, the data direction of the MOSI, MISO, SCK and SS

pins is

overridden according to Table 22.

Table 22. SPI Pin Overrides

Pin Direction, Master SPI Direction, Slave SPI

MOSI User Defined Input

MISO Input User Defined

SCK User Defined Input

User Defined Input

Note: See “Alternate Functions of Port B” on page 79 for a detailed description of how to

define the direction of the user-defined SPI pins.

1041H–11/01

SS Pin Functionality When the SPI is configured as a master (MSTR in SPCR is set), the user can determine

the direction of the SS pin, which does not affect the SPI system. If SS high to ensure master SPI operation. If the SS when the SPI is configured as master with the SS tem interprets this as another master selecting the SPI as a slave and starting to send data to it. To avoid bus contention, the SPI system takes the following actions:

1. The MSTR bit in SPCR is cleared and the SPI system becomes a slave. As a result of the SPI becoming a slave, the MOSI and SCK pins become inputs.

2. The SPIF flag in SPSR is set and if the SPI interrupt is enabled and the I-bit in SREG are set, the interrupt routine will be executed.

Thus, when interrupt-driven SPI transmission is used in Master Mode and there exists a possibility that SS still set. Once the MSTR bit has been cleared by a slave select, it must be set by the user to re-enable the SPI Master Mode.

pin. If SS is configured as an output, the pin is a general output

is configured as an input, it must be held

pin is driven low by peripheral circuitry

pin defined as an input, the SPI sys-

is driven low, the interrupt should always check that the MSTR bit is

When the SPI is configured as a slave, the SS

pin is always input. When SS is held low, the SPI is activated and MISO becomes an output if configured so by the user. All other pins are inputs. When SS

is driven high, all pins are inputs and the SPI is passive, which means that it will not receive incoming data. Note that the SPI logic will be reset once the SS

pin is brought high. If the SS pin is brought high during a transmission, the SPI will stop sending and receiving immediately and both data received and data sent must be considered as lost.

Data Modes There are four combinations of SCK phase and polarity with respect to serial data,

which are determined by control bits CPHA and CPOL. The SPI data transfer formats are shown in Figure 39 and Figure 40.

Figure 39. SPI Transfer Format with CPHA = 0 and DORD = 0

SCK CYCLE#

(FOR REFERENCE)

SCK (CPOL=0) SCK (CPOL=1)

MOSI

(FROM MASTER)

MISO

(FROM SLAVE)

SS (TO SLAVE)

SAMPLE

1234 56 78

MSB 123456 LSB

*Not defined but normally MSB of character just received.

AT90S/LS8535

1041H–11/01

SPI Control Register – SPCR

AT90S/LS8535

Figure 40. SPI Transfer Format with CPHA = 1 and DORD = 0

Bit 76543210

$0D ($2D) SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0 SPCR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – SPIE: SPI Interrupt Enable

This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR register is set and the global interrupts are enabled.

• Bit 6 – SPE: SPI Enable

When the SPE bit is set (one), the SPI is enabled. This bit must be set to enable any SPI operations.

• Bit 5 – DORD: Data Order

When the DORD bit is set (one), the LSB of the data word is transmitted first.

When the DORD bit is cleared (zero), the MSB of the data word is transmitted first.

• Bit 4 – MSTR: Master/Slave Select

This bit selects Master SPI Mode when set (one) and Slave SPI Mode when cleared (zero). If SS

is configured as an input and is driven low while MSTR is set, MSTR will be cleared and SPIF in SPSR will become set. The user will then have to set MSTR to reenable SPI Master Mode.

• Bit 3 – CPOL: Clock Polarity

When this bit is set (one), SCK is high when idle. When CPOL is cleared (zero), SCK is low when idle. Refer to Figure 39. and Figure 40. for additional information.

• Bit 2 – CPHA: Clock Phase

Refer to Figure 40 or Figure 41 for the functionality of this bit.

1041H–11/01

• Bits 1,0 – SPR1, SPR0: SPI Clock Rate Select 1 and 0

These two bits control the SCK rate of the device configured as a master. SPR1 and SPR0 have no effect on the slave. The relationship between SCK and the oscillator clock frequency f

is shown in Table 23.

Table 23. Relationship between SCK and the Oscillator Frequency

SPR1 SPR0 SCK Frequency

SPI Status Register – SPSR

00 f

01 f

10 f

11 f

Bit 76543210

$0E ($2E) SPIF WCOL ––––––SPSR

Read/WriteRRRRRRRR

Initial Value 0 0 0 0 0 0 0 0

/16

/64

/128

• Bit 7 – SPIF: SPI Interrupt Flag

When a serial transfer is complete, the SPIF bit is set (one) and an interrupt is generated if SPIE in SPCR is set (one) and global interrupts are enabled. If SS

is an input and is driven low when the SPI is in Master Mode, this will also set the SPIF flag. SPIF is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by first reading the SPI Status Register with SPIF set (one), then accessing the SPI Data Register (SPDR).

• Bit 6 – WCOL: Write Collision flag

The WCOL bit is set if the SPI Data Register (SPDR) is written during a data transfer. The WCOL bit (and the SPIF bit) are cleared (zero) by first reading the SPI Status Register with WCOL set (one) and then accessing the SPI Data Register.

• Bit 5..0 – Res: Reserved Bits

SPI Data Register – SPDR

AT90S/LS8535

These bits are reserved bits in the AT90S8535 and will always read as zero.

The SPI interface on the AT90S8535 is also used for program memory and EEPROM downloading or uploading. See page 99 for serial programming and verification.

Bit 76543210

$0F ($2F) MSB LSB SPDR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value X X X X X X X X Undefined

The SPI Data Register is a read/write register used for data transfer between the register file and the SPI Shift Register. Writing to the register initiates data transmission. Reading the register causes the Shift Register Receive buffer to be read.

1041H–11/01

AT90S/LS8535

UART The AT90S8535 features a full duplex (separate receive and transmit registers) Univer-

sal Asynchronous Receiver and Transmitter (UART). The main features are:

Baud Rate Generator that can Generate a Large Number of Baud Rates (bps)

•

• High Baud Rates at Low XTAL Frequencies

• 8 or 9 Bits Data

• Noise Filtering

• Overrun Detection

• Framing Error Detection

• False Start Bit Detection

• Three Separate Interrupts on TX Complete, TX Data Register Empty and RX Complete

• Buffered Transmit and Receive

Data Transmission A block schematic of the UART transmitter is shown in Figure 41.

Figure 41. UART Transmitter

1041H–11/01

Data transmission is initiated by writing the data to be transmitted to the UART I/O Data Register, UDR. Data is transferred from UDR to the Transmit shift register when:

• A new character is written to UDR after the stop bit from the previous character has

been shifted out. The shift register is loaded immediately.

• A new character is written to UDR before the stop bit from the previous character

has been shifted out. The shift register is loaded when the stop bit of the character currently being transmitted is shifted out.

If the 10(11)-bit Transmitter shift register is empty, data is transferred from UDR to the shift register. The UDRE (UART Data Register Empty) bit in the UART Status Register, USR, is set. When this bit is set (one), the UART is ready to receive the next character. At the same time as the data is transferred from UDR to the 10(11)-bit shift register, bit 0 of the shift register is cleared (start bit) and bit 9 or 10 is set (stop bit). If 9-bit data word

is selected (the CHR9 bit in the UART Control Register, UCR is set), the TXB8 bit in UCR is transferred to bit 9 in the Transmit shift register.

On the baud rate clock following the transfer operation to the shift register, the start bit is shifted out on the TXD pin. Then follows the data, LSB first. When the stop bit has been shifted out, the shift register is loaded if any new data has been written to the UDR during the transmission. During loading, UDRE is set. If there is no new data in the UDR register to send when the stop bit is shifted out, the UDRE flag will remain set until UDR is written again. When no new data has been written and the stop bit has been present on TXD for one bit length, the TX Complete flag (TXC) in USR is set.

The TXEN bit in UCR enables the UART Transmitter when set (one). When this bit is cleared (zero), the PD1 pin can be used for general I/O. When TXEN is set, the UART Transmitter will be connected to PD1, which is forced to be an output pin regardless of the setting of the DDD1 bit in DDRD.

Data Reception Figure 42 shows a block diagram of the UART Receiver.

Figure 42. UART Receiver

The receiver front-end logic samples the signal on the RXD pin at a frequency 16 times the baud rate. While the line is idle, one single sample of logical “0” will be interpreted as the falling edge of a start bit and the start bit detection sequence is initiated. Let sample

AT90S/LS8535

1041H–11/01

AT90S/LS8535

1 denote the first zero-sample. Following the 1-to-0 transition, the receiver samples the RXD pin at samples 8, 9 and 10. If two or more of these three samples are found to be logical “1”s, the start bit is rejected as a noise spike and the receiver starts looking for the next 1-to-0 transition.

If however, a valid start bit is detected, sampling of the data bits following the start bit is performed. These bits are also sampled at samples 8, 9 and 10. The logical value found in at least two of the three samples is taken as the bit value. All bits are shifted into the Transmitter Shift register as they are sampled. Sampling of an incoming character is shown in Figure 43.

Figure 43. Sampling Received Data

When the stop bit enters the receiver, the majority of the three samples must be one to accept the stop bit. If two or more samples are logical “0”s, the Framing Error (FE) flag in the UART Status Register (USR) is set. Before reading the UDR register, the user should always check the FE bit to detect framing errors.

Whether or not a valid stop bit is detected at the end of a character reception cycle, the data is transferred to UDR and the RXC flag in USR is set. UDR is in fact two physically separate registers, one for transmitted data and one for received data. When UDR is read, the Receive Data register is accessed and when UDR is written, the Transmit Data register is accessed. If 9-bit data word is selected (the CHR9 bit in the UART Control Register, UCR is set), the RXB8 bit in UCR is loaded with bit 9 in the Transmit Shift register when data is transferred to UDR.

If, after having received a character, the UDR register has not been read since the last receive, the OverRun (OR) flag in UCR is set. This means that the last data byte shifted into the shift register could not be transferred to UDR and has been lost. The OR bit is buffered and is updated when the valid data byte in UDR is read. Thus, the user should always check the OR bit after reading the UDR register in order to detect any overruns if the baud rate is high or CPU load is high.

When the RXEN bit in the UCR register is cleared (zero), the receiver is disabled. This means that the PD0 pin can be used as a general I/O pin. When RXEN is set, the UART Receiver will be connected to PD0, which is forced to be an input pin regardless of the setting of the DDD0 bit in DDRD. When PD0 is forced to input by the UART, the PORTD0 bit can still be used to control the pull-up resistor on the pin.

When the CHR9 bit in the UCR register is set, transmitted and received characters are 9 bits long, plus start and stop bits. The ninth data bit to be transmitted is the TXB8 bit in UCR register. This bit must be set to the wanted value before a transmission is initiated by writing to the UDR register. The ninth data bit received is the RXB8 bit in the UCR register.

1041H–11/01

UART Control

UART I/O Data Register – UDR

UART Status Register – USR

Bit 76543210

$0C ($2C) MSB LSB UDR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

The UDR register is actually two physically separate registers sharing the same I/O address. When writing to the register, the UART Transmit Data register is written. When reading from UDR, the UART Receive Data register is read.

Bit 76543210

$0B ($2B) RXC TXC UDRE FE OR –––USR

Read/Write R R/W R R R R R R

Initial Value 0 0 1 0 0 0 0 0

The USR register is a read-only register providing information on the UART status.

• Bit 7 – RXC: UART Receive Complete

This bit is set (one) when a received character is transferred from the Receiver Shift register to UDR. The bit is set regardless of any detected framing errors. When the RXCIE bit in UCR is set, the UART Receive Complete interrupt will be executed when RXC is set (one). RXC is cleared by reading UDR. When interrupt-driven data reception is used, the UART Receive Complete Interrupt routine must read UDR in order to clear RXC, otherwise a new interrupt will occur once the interrupt routine terminates.

• Bit 6 – TXC: UART Transmit Complete

This bit is set (one) when the entire character (including the stop bit) in the Transmit Shift register has been shifted out and no new data has been written to UDR. This flag is especially useful in half-duplex communications interfaces, where a transmitting application must enter receive mode and free the communications bus immediately after completing the transmission.

When the TXCIE bit in UCR is set, setting of TXC causes the UART Transmit Complete interrupt to be executed. TXC is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, the TXC bit is cleared (zero) by writing a logical “1” to the bit.

• Bit 5 – UDRE: UART Data Register Empty

This bit is set (one) when a character written to UDR is transferred to the Transmit Shift register. Setting of this bit indicates that the transmitter is ready to receive a new character for transmission.

When the UDRIE bit in UCR is set, the UART Transmit Complete interrupt to be executed as long as UDRE is set. UDRE is cleared by writing UDR. When interrupt-driven data transmission is used, the UART Data Register Empty Interrupt routine must write UDR in order to clear UDRE, otherwise a new interrupt will occur once the interrupt routine terminates.

UDRE is set (one) during reset to indicate that the transmitter is ready.

• Bit 4 – FE: Framing Error

This bit is set if a Framing Error condition is detected, i.e., when the stop bit of an incoming character is zero.

AT90S/LS8535

1041H–11/01

UART Control Register – UCR

AT90S/LS8535

The FE bit is cleared when the stop bit of received data is one.

• Bit 3 – OR: OverRun

This bit is set if an Overrun condition is detected, i.e., when a character already present in the UDR register is not read before the next character has been shifted into the Receiver Shift register. The OR bit is buffered, which means that it will be set once the valid data still in UDR is read.

The OR bit is cleared (zero) when data is received and transferred to UDR.

• Bits 2..0 – Res: Reserved Bits

These bits are reserved bits in the AT90S8535 and will always read as zero.

Bit 76543210

$0A ($2A) RXCIE TXCIE UDRIE RXEN TXEN CHR9 RXB8 TXB8 UCR

Read/Write R/W R/W R/W R/W R/W R/W R W

Initial Value 0 0 0 0 0 0 1 0

• Bit 7 – RXCIE: RX Complete Interrupt Enable

When this bit is set (one), a setting of the RXC bit in USR will cause the Receive Complete Interrupt routine to be executed provided that global interrupts are enabled.

• Bit 6 – TXCIE: TX Complete Interrupt Enable

When this bit is set (one), a setting of the TXC bit in USR will cause the Transmit Complete Interrupt routine to be executed provided that global interrupts are enabled.

• Bit 5 – UDRIE: UART Data Register Empty Interrupt Enable

When this bit is set (one), a setting of the UDRE bit in USR will cause the UART Data Register Empty Interrupt routine to be executed provided that global interrupts are enabled.

• Bit 4 – RXEN: Receiver Enable

This bit enables the UART receiver when set (one). When the receiver is disabled, the RXC, OR and FE status flags cannot become set. If these flags are set, turning off RXEN does not cause them to be cleared.

• Bit 3 – TXEN: Transmitter Enable

This bit enables the UART transmitter when set (one). When disabling the transmitter while transmitting a character, the transmitter is not disabled before the character in the shift register plus any following character in UDR has been completely transmitted.

• Bit 2 – CHR9: 9 Bit Characters

When this bit is set (one), transmitted and received characters are 9 bits long, plus start and stop bits. The ninth bit is read and written by using the RXB8 and TXB8 bits in UCR, respectively. The ninth data bit can be used as an extra stop bit or a parity bit.

• Bit 1 – RXB8: Receive Data Bit 8

When CHR9 is set (one), RXB8 is the ninth data bit of the received character.

• Bit 0 – TXB8: Transmit Data Bit 8

1041H–11/01

When CHR9 is set (one), TXB8 is the ninth data bit in the character to be transmitted.

Baud Rate Generator The baud rate generator is a frequency divider which generates baud rates according to

the following equation:

BAUD

--------------------------------------=

16(UBRR 1 )+

• BAUD = Baud rate

• f

= Crystal clock frequency

• UBRR = Contents of the UART Baud Rate register, UBRR (0 - 255)

For standard crystal frequencies, the most commonly used baud rates can be generated by using the UBRR settings in Table 24. UBRR values that yield an actual baud rate differing less than 2% from the target baud rate are boldface in the table. However, using baud rates that have more than 1% error is not recommended. High error ratings give less noise resistance. Table 24. UBRR Settings at Various Crystal Frequencies (Examples)

Baud Rate

2400 4800

9600 14400 19200 28800 38400 57600 76800

115200

Baud Rate

2400

4800

9600 14400 19200 28800 38400 57600 76800

115200

Baud Rate

2400

4800

9600 14400 19200 28800 38400 57600 76800

115200

1MHz

UBRR= UBRR= UBRR= 6 7. 5 UBRR= UBRR= 3 7. 8 UBRR= UBRR= 2 7. 8 UBRR= UBRR= 1 7. 8 UBRR= UBRR= 1 2 2.9 UBRR= UBRR= 0 7. 8 UBRR= UBRR= 0 22.9 UBRR= 1 33.3 UBRR= 1 22.9 UBRR= UBRR= 0 8 4.3 UBRR=

3.2768 MHz

UBRR= UBRR= UBRR= UBRR= UBRR= 10 3 .1 UBRR= UBRR= UBRR= 4 6. 3 UBRR= UBRR= 3 1 2.5 UBRR= UBRR= 2 1 2.5 UBRR= UBRR= 1 1 2.5 UBRR=

7.3728 MHz

UBRR= UBRR= UBRR= UBRR= UBRR= UBRR= UBRR= UBRR= UBRR= UBRR=

%Error

25 0.2 12 0.2

%Error

84 0.4 42 0.8 20 1.6 13 1.6

61.6

%Error

191 0.0

95 0.0 47 0.0 31 0.0 23 0.0 15 0.0 11 0.0

70.0

50.0

30.0

1.8432 MHz

UBRR= UBRR=

3.6864 MHz

UBRR= UBRR= UBRR= UBRR=

UBRR=

8MHz

UBRR= UBRR= UBRR= UBRR= UBRR= UBRR= 16 2 .1 UBRR= UBRR= UBRR= 8 3. 7 UBRR= UBRR= 6 7. 5 UBRR= 7 6.7 UB RR= UBRR= 3 7. 8 UBRR=

%Error

47 0.0 23 0.0 11 0.0

70.0

50.0

30.0

20.0

10.0

00.0

%Error

95 0.0 47 0.0 23 0.0 15 0.0 11 0.0

70.0

50.0

30.0

20.0

10.0

%Error

207 0.2 103 0.2

51 0.2 34 0.8 25 0.2

12 0.2

%Error

2MHz

UBRR= UBRR= UBRR= UBRR= 8 3.7 UBRR= 10 3.1 UBRR= 6 7. 5 UBRR= UBRR= 3 7. 8 UBRR= 4 6.3 UBRR= 2 7. 8 UBRR= UBRR= 1 7.8 UBRR= 2 12.5

UBRR= 0 7.8 UBRR= 0 25.0

UBRR= UBRR= UBRR= UBRR= 16 2 .1 UBRR= UBRR= UBRR= 8 3. 7 UBRR= UBRR= 6 7. 5 UBRR= 7 6.7 UBRR= 3 7. 8 UBRR= UBRR= 2 7. 8 UBRR= 3 6.7 UBRR= 1 7.8 UBRR= 2 20.0

9.216 MHz

UBRR= UBRR= UBRR= UBRR= UBRR=

UBRR=

51 0.2 25 0.2 12 0.2

4MHz

103 0.2

51 0.2 25 0.2

12 0.2

239 0.0 119 0.0

59 0.0 39 0.0 29 0.0 19 0.0 14 0.0

%Error

90.0

40.0

2.4576 MHz

UBRR= UBRR= UBRR=

4.608 MHz

UBRR= UBRR= UBRR=

UBRR=

11.059 MHz

UBRR= 28 7 UBRR= UBRR= UBRR= UBRR= UBRR= UBRR= UBRR=

UBRR=

%Error

63 0.0 31 0.0 15 0.0

70.0

30.0

10.0

%Error

119 0.0

59 0.0 29 0.0 19 0.0 14 0.0

90.0

40.0

%Error

143 0.0

71 0.0 47 0.0 35 0.0 23 0.0 17 0.0 11 0.0

80.0

50.0

Note: Maximum baud rate to each frequency.

AT90S/LS8535

1041H–11/01

UART Baud Rate Register – UBRR

AT90S/LS8535

Bit 76543210

$09 ($29) MSB LSB UBRR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

The UBRR register is an 8-bit read/write register that specifies the UART Baud Rate according to the equation on the previous page.

1041H–11/01

Analog Comparator The Analog Comparator compares the input values on the positive input PB2 (AIN0) and

negative input PB3 (AIN1). When the voltage on the positive input PB2 (AIN0) is higher than the voltage on the negative input PB3 (AIN1), the Analog Comparator Output (ACO) is set (one). The comparator’s output can be set to trigger the Timer/Counter1 Input Capture function. In addition, the comparator can trigger a separate interrupt, exclusive to the Analog Comparator. The user can select Interrupt triggering on comparator output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is shown in Figure 44.

Figure 44. Analog Comparator Block Diagram

Analog Comparator Control and Status Register – ACSR

Bit 76543210

$08 ($28) ACD – ACO ACI ACIE ACIC ACIS1 ACIS0 ACSR

Read/Write R/W R R R/W R/W R/W R/W R/W

Initial Value 0 0 N/A 0 0 0 0 0

• Bit 7 – ACD: Analog Comparator Disable

When this bit is set (one), the power to the Analog Comparator is switched off. This bit can be set at any time to turn off the Analog Comparator. When changing the ACD bit, the Analog Comparator interrupt must be disabled by clearing the ACIE bit in ACSR. Otherwise an interrupt can occur when the bit is changed.

• Bit 6 – Res: Reserved Bit

This bit is a reserved bit in the AT90S8535 and will always read as zero.

• Bit 5 – ACO: Analog Comparator Output

ACO is directly connected to the comparator output.

• Bit 4 – ACI: Analog Comparator Interrupt Flag

This bit is set (one) when a comparator output event triggers the interrupt mode defined by ACI1 and ACI0. The Analog Comparator Interrupt routine is executed if the ACIE bit is set (one) and the I-bit in SREG is set (one). ACI is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, ACI is cleared by writing a logical “1” to the flag.

• Bit 3 – ACIE: Analog Comparator Interrupt Enable

When the ACIE bit is set (one) and the I-bit in the Status Register is set (one), the Analog Comparator interrupt is activated. When cleared (zero), the interrupt is disabled.

AT90S/LS8535

1041H–11/01

AT90S/LS8535

• Bit 2 – ACIC: Analog Comparator Input Capture Enable

When set (one), this bit enables the Input Capture function in Timer/Counter1 to be triggered by the Analog Comparator. The comparator output is in this case directly connected to the Input Capture front-end logic, making the comparator utilize the noise canceler and edge select features of the Timer/Counter1 Input Capture interrupt. When cleared (zero), no connection between the Analog Comparator and the Input Capture function is given. To make the comparator trigger the Timer/Counter1 Input Capture interrupt, the TICIE1 bit in the Timer Interrupt Mask Register (TIMSK) must be set (one).

• Bits 1,0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select

These bits determine which comparator events trigger the Analog Comparator interrupt. The different settings are shown in Table 25.

Table 25. ACIS1/ACIS0 Settings

ACIS1 ACIS0 Interrupt Mode

0 0 Comparator Interrupt on Output Toggle

01Reserved

1 0 Comparator Interrupt on Falling Output Edge

1 1 Comparator Interrupt on Rising Output Edge

Note: When changing the ACIS1/ACIS0 bits, the Analog Comparator interrupt must be dis-

abled by clearing its interrupt enable bit in the ACSR register. Otherwise an interrupt can occur when the bits are changed.

Caution: Using the SBI or CBI instruction on bits other than ACI in this register will write a “1” back into ACI if it is read as set, thus clearing the flag.

1041H–11/01

Analog-to-Digital Converter

Feature list • 10-bit Resolution

• 0.5 LSB Integral Non-linearity

• ±2 LSB Absolute Accuracy

• 65 - 260 µs Conversion Time

• Up to 15 kSPS at Maximum Resolution

• 8 Multiplexed Input Channels

• Rail-to-Rail Input Range

• Free Running or Single Conversion Mode

• Interrupt on ADC Conversion Complete

• Sleep Mode Noise Canceler

The AT90S8535 features a 10-bit successive approximation ADC. The ADC is connected to an 8-channel Analog Multiplexer that allows each pin of Port A to be used as an input for the ADC. The ADC contains a Sample and Hold Amplifier that ensures that the input voltage to the ADC is held at a constant level during conversion. A block diagram of the ADC is shown in Figure 45.

The ADC has two separate analog supply voltage pins, AVCC and AGND. AGND must be connected to GND and the voltage on AV

. See “ADC Noise Canceling Techniques” on page 74 on how to connect these pins.

An external reference voltage must be applied to the AREF pin. This voltage must be in the range 2V - AV

must not differ more than ±0.3V from

Figure 45. Analog-to-Digital Converter Block Schematic

ADC CONVERSION

COMPLETE IRQ

8-BIT DATA BUS

ADIF

ADC CTRL & STATUS

ADIF

ADFR

ADSC

ADEN

AREF

ADC7

ADC6

ADC5

ADC4

ADC3

ADC2

ADC1

ADC0

CHANNEL

MUX

ADC MULTIPLEXER

SELECT (ADMUX)

SAMPLE & HOLD COMPARATOR

MUX2

MUX1

MUX0

ADIE

ADPS2

PRESCALER

CONVERSION LOGIC10-BIT DAC

15 0

ADC DATA REGISTER

ADPS0

ADPS1

(ADCH/ADCL)

ADC9..0

AT90S/LS8535

1041H–11/01

AT90S/LS8535

Operation The ADC converts an analog input voltage to a 10-bit digital value through successive

approximation. The minimum value represents AGND and the maximum value represents the voltage on the AREF pin minus one LSB. The analog input channel is selected by writing to the MUX bits in ADMUX. Any of the eight ADC input pins ADC7..0 can be selected as single-ended inputs to the ADC.

The ADC can operate in two modes – Single Conversion and Free Running. In Single Conversion Mode, each conversion will have to be initiated by the user. In Free Running Mode, the ADC is constantly sampling and updating the ADC Data Register. The ADFR bit in ADCSR selects between the two available modes.

The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSR. Input channel selections will not go into effect until ADEN is set. The ADC does not consume power when ADEN is cleared, so it is recommended to switch off the ADC before entering power-saving sleep modes.

A conversion is started by writing a logical “1” to the ADC Start Conversion bit, ADSC. This bit stays high as long as the conversion is in progress and will be set to zero by hardware when the conversion is completed. If a different data channel is selected while a conversion is in progress, the ADC will finish the current conversion before performing the channel change.

The ADC generates a 10-bit result, which is presented in the ADC data register, ADCH and ADCL. When reading data, ADCL must be read first, then ADCH, to ensure that the content of the data register belongs to the same conversion. Once ADCL is read, ADC access to data register is blocked. This means that if ADCL has been read and a conversion completes before ADCH is read, neither register is updated and the result from the conversion is lost. Then ADCH is read, ADC access to the ADCH and ADCL register is re-enabled.

The ADC has its own interrupt that can be triggered when a conversion completes. When ADC access to the data registers is prohibited between reading of ADCH and ADCL, the interrupt will trigger even if the result is lost.

Prescaling Figure 46. ADC Prescaler

ADEN

ADPS0 ADPS1 ADPS2

The successive approximation circuitry requires an input clock frequency between 50 kHz and 200 kHz to achieve maximum resolution. If a resolution of lower than 10 bits is required, the input clock frequency to the ADC can be higher than 200 kHz to achieve a

Reset

7-BIT ADC PRESCALER

CK/2

CK/4

ADC CLOCK SOURCE

CK/8

CK/16

CK/64

CK/32

CK/128

1041H–11/01

higher sampling rate. See “ADC Characteristics” on page 75 for more details. The ADC module contains a prescaler, which divides the system clock to an acceptable ADC clock frequency.

The ADPS2..0 bits in ADCSR are used to generate a proper ADC clock input frequency from any CPU frequency above 100 kHz. The prescaler starts counting from the moment the ADC is switched on by setting the ADEN bit in ADCSR. The prescaler keeps running for as long as the ADEN bit is set and is continuously reset when ADEN is low.

When initiating a conversion by setting the ADSC bit in ADCSR, the conversion starts at the following rising edge of the ADC clock cycle.

A normal conversion takes 13 ADC clock cycles. In certain situations, the ADC needs more clock cycles for initialization and to minimize offset errors. Extended conversions take 25 ADC clock cycles and occur as the first conversion after the ADC is switched on (ADEN in ADCSR is set).

The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conversion and 13.5 ADC clock cycles after the start of an extended conversion. When a conversion is complete, the result is written to the ADC data registers and ADIF is set. In Single Conversion Mode, ADSC is cleared simultaneously. The software may then set ADSC again and a new conversion will be initiated on the first rising ADC clock edge. In Free Running Mode, a new conversion will be started immediately after the conversion completes, while ADSC remains high. Using Free Running Mode and an ADC clock frequency of 200 kHz gives the lowest conversion time with a maximum resolution, 65 µs, equivalent to 15 kSPS. For a summary of conversion times, see Table

26.

Figure 47. ADC Timing Diagram, Extended Conversion (Single Conversion Mode)

Next Conversion

1 2

Sign and MSB of result

LSB of result

MUX and REFS update

Cycle number

ADC clock

ADEN

ADSC

ADIF

ADCH

ADCL

1 212

MUX and REFS update

14 15

Extended Conversion

16 17

Sample & hold

19 20 21 22 23

Conversion

complete

24 25

AT90S/LS8535

1041H–11/01

Figure 48. ADC Timing Diagram, Single Conversion

One Conversion Next Conversion

2 3 4 5 6 7 8

Cycle number

ADC clock

ADSC

ADIF

AT90S/LS8535

10 11 12 13

ADCH

ADCL

Sample & hold

MUX and REFS update

Conversion

complete

Figure 49. ADC Timing Diagram, Free Running Conversion

One Conversion Next Conversion

Cycle number

ADC clock

ADSC

ADIF

ADCH

ADCL

Conversion

11 12 13

complete

Sign and MSB of result

LSB of result

MUX and REFS update

Sample & hold

Sign and MSB of result

LSB of result

MUX and REFS update

ADC Noise Canceler Function

1041H–11/01

Table 26. ADC Conversion Time

Sample and Hold (Cycles

Condition

from Start of Conversion)

Extended Conversion 14 25 125 - 500

Normal Conversion 14 26 130 - 520

Conversion

Time (Cycles)

Conversion

Time (µs)

The ADC features a noise canceler that enables conversion during Idle Mode to reduce noise induced from the CPU core. To make use of this feature, the following procedure should be used:

1. Make sure that the ADC is enabled and is not busy converting. Single Conversion Mode must be selected and the ADC conversion complete interrupt must be enabled.

ADEN = 1 ADSC = 0 ADFR = 0 ADIE = 1

ADC Multiplexer Select Register – ADMUX

2. Enter Idle Mode. The ADC will start a conversion once the CPU has been halted.

3. If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake up the MCU and execute the ADC Conversion Complete Interrupt routine.

Bit 76543210

$07 ($27) –––––MUX2 MUX1 MUX0 ADMUX

Read/Write R R R R R R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

• Bits 7..3 – Res: Reserved Bits

These bits are reserved bits in the AT90S8535 and always read as zero.

• Bits 2..0 – MUX2..MUX0: Analog Channel Select Bits 2-0

The value of these three bits selects which analog input ADC7..0 is connected to the ADC. See Table 27 for details.

If these bits are changed during a conversion, the change will not go into effect until this conversion is complete (ADIF in ADCSR is set).

Table 27. Input Channel Selections

MUX2.0 Single-ended Input

000 ADC0

001 ADC1

ADC Control and Status Register – ADCSR

010 ADC2

011 ADC3

100 ADC4

101 ADC5

110 ADC6

111 ADC7

Bit 76543210

$06 ($26) ADEN ADSC ADFR ADIF ADIE ADPS2 ADPS1 ADPS0 ADCSR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – ADEN: ADC Enable

Writing a logical “1” to this bit enables the ADC. By clearing this bit to zero, the ADC is turned off. Turning the ADC off while a conversion is in progress will terminate this conversion.

• Bit 6 – ADSC: ADC Start Conversion

In Single Conversion Mode, a logical “1” must be written to this bit to start each conversion. In Free Running Mode, a logical “1” must be written to this bit to start the first conversion. The first time ADSC has been written after the ADC has been enabled or if ADSC is written at the same time as the ADC is enabled, an extended conversion will precede the initiated conversion. This extended conversion performs initialization of the ADC.

AT90S/LS8535

1041H–11/01

AT90S/LS8535

ADSC will read as one as long as a conversion is in progress. When the conversion is complete, it returns to zero. When a extended conversion precedes a real conversion, ADSC will stay high until the real conversion completes. Writing a “0” to this bit has no effect.

• Bit 5 – ADFR: ADC Free Running Select

When this bit is set (one), the ADC operates in Free Running Mode. In this mode, the ADC samples and updates the data registers continuously. Clearing this bit (zero) will terminate Free Running Mode.

• Bit 4 – ADIF: ADC Interrupt Flag

This bit is set (one) when an ADC conversion completes and the data registers are updated. The ADC Conversion Complete interrupt is executed if the ADIE bit and the Ibit in SREG are set (one). ADIF is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, ADIF is cleared by writing a logical “1” to the flag. Beware that if doing a read-modify-write on ADCSR, a pending interrupt can be disabled. This also applies if the SBI and CBI instructions are used.

• Bit 3 – ADIE: ADC Interrupt Enable

When this bit is set (one) and the I-bit in SREG is set (one), the ADC Conversion Complete interrupt is activated.

• Bits 2..0 – ADPS2..ADPS0: ADC Prescaler Select Bits

ADC Data Register – ADCL AND ADCH

These bits determine the division factor between the XTAL frequency and the input clock to the ADC.

Table 28. ADC Prescaler Selections

ADPS2 ADPS1 ADPS0 Division Factor

000 2

001 2

010 4

011 8

100 16

101 32

110 64

111 128

Bit 151413121110 9 8

$05 ($25) ––––––ADC9 ADC8 ADCH

$04 ($24) ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 ADCL

76543210

Read/WriteRRRRRRRR

RRRRRRRR

Initial Value 0 0 0 0 0 0 0 0

00000000

1041H–11/01

When an ADC conversion is complete, the result is found in these two registers.

When ADCL is read, the ADC Data Register is not updated until ADCH is read. Consequently, it is essential that both registers are read and that ADCL is read before ADCH.

• ADC9..0: ADC Conversion result

These bits represent the result from the conversion. $000 represents analog ground and $3FF represents the selected reference voltage minus one LSB.

Scanning Multiple Channels

ADC Noise Canceling Techniques

Since change of analog channel always is delayed until a conversion is finished, the Free Running Mode can be used to scan multiple channels without interrupting the converter. Typically, the ADC Conversion Complete interrupt will be used to perform the channel shift. However, the user should take the following fact into consideration: The interrupt triggers once the result is ready to be read. In Free Running Mode, the next conversion will start immediately when the interrupt triggers. If ADMUX is changed after the interrupt triggers, the next conversion has already started and the old setting is used.

Digital circuitry inside and outside the AT90S8535 generates EMI that might affect the accuracy of analog measurements. If conversion accuracy is critical, the noise level can be reduced by applying the following techniques:

1. The analog part of the AT90S8535 and all analog components in the application should have a separate analog ground plane on the PCB. This ground plane is connected to the digital ground plane via a single point on the PCB.

2. Keep analog signal paths as short as possible. Make sure analog tracks run over the analog ground plane and keep them well away from high-speed switching digital tracks.

3. The AV

pin on the AT90S8535 should be connected to the digital VCC supply

voltage via an LC network as shown in Figure 50.

4. Use the ADC noise canceler function to reduce induced noise from the CPU.

5. If some Port A pins are used as digital outputs, it is essential that these do not switch while a conversion is in progress.

Figure 50. ADC Power Connections

VCC

GND

PA0 (ADC0)

43 4142 4044

AT90S8535

PA1 (ADC1)

PA2 (ADC2)

PA3 (ADC3)

PA4 (ADC4)

PA5 (ADC5)

PA6 (ADC6)

PA7 (ADC7)

AREF

AGND

AVCC

PC0

Analog Ground Plane

10µΗ

100nF

AT90S/LS8535

1041H–11/01

AT90S/LS8535

ADC Characteristics

TA = -40°C to 85°C

Symbol Parameter Condition Min Typ Max Units

Resolution 10 Bits

Absolute accuracy

Integral Non-linearity V

Differential Non-linearity V

Zero Error (Offset) 1 LSB

Conversion Time 65 260 µs

Clock Frequency 50 200 kHz

REF

AIN

Analog Supply Voltage VCC - 0.3

Reference Voltage 2 AV

Reference Input Resistance 6 10 13 kΩ

Input Voltage AGND AREF V

Analog Input Resistance 100 MΩ

Notes: 1. Minimum for AVCC is 2.7V.

2. Maximum for AV

is 6.0V.

VREF = 4V ADC clock = 200 kHz

VREF = 4V ADC clock = 1 MHz

VREF = 4V ADC clock = 2 MHz

> 2V 0.5 LSB

REF

> 2V 0.5 LSB

REF

(1)

12LSB

4LSB

16 LSB

VCC + 0.3

(2)

1041H–11/01

I/O Ports All AVR ports have true read-modify-write functionality when used as general digital I/O

ports. This means that the direction of one port pin can be changed without unintentionally changing the direction of any other pin with the SBI and CBI instructions. The same applies for changing drive value (if configured as output) or enabling/disabling of pull-up resistors (if configured as input).

Port A Port A is an 8-bit bi-directional I/O port.

Three I/O memory address locations are allocated for Port A, one each for the Data Register – PORTA, $1B($3B), Data Direction Register – DDRA, $1A($3A) and the Port A Input Pins – PINA, $19($39). The Port A Input Pins address is read-only, while the Data Register and the Data Direction Register are read/write.

All port pins have individually selectable pull-up resistors. The Port A output buffers can sink 20 mA and thus drive LED displays directly. When pins PA0 to PA7 are used as inputs and are externally pulled low, they will source current if the internal pull-up resistors are activated.

Port A has an alternate function as analog inputs for the ADC. If some Port A pins are configured as outputs, it is essential that these do not switch when a conversion is in progress. This might corrupt the result of the conversion.

During Power-down mode, the Schmitt trigger of the digital input is disconnected. This allows analog signals that are close to V causing excessive power consumption.

/2 to be present during power-down without

Port A Data Register – PORTA

Port A Data Direction Register – DDRA

Port A Input Pins Address – PINA

Bit 76543210

$1B ($3B)

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

$1A ($3A) DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 DDRA

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

$19 ($39) PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 PINA

Read/WriteRRRRRRRR

Initial Value N/A N/A N/A N/A N/A N/A N/A N/A

PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 PORTA

The Port A Input Pins address (PINA) is not a register; this address enables access to the physical value on each Port A pin. When reading PORTA, the Port A Data Latch is read and when reading PINA, the logical values present on the pins are read.

AT90S/LS8535

1041H–11/01

AT90S/LS8535

Port A as General Digital I/O All eight pins in Port A have equal functionality when used as digital I/O pins.

PAn, general I/O pin: The DDAn bit in the DDRA register selects the direction of this pin. If DDAn is set (one), PAn is configured as an output pin. If DDAn is cleared (zero), PAn is configured as an input pin. If PORTAn is set (one) when the pin is configured as an input pin, the MOS pull-up resistor is activated. To switch the pull-up resistor off, the PORTAn has to be cleared (zero) or the pin has to be configured as an output pin.The port pins are tri-stated when a reset condition becomes active, even if the clock is not running.

Table 29. DDAn Effects on Port A Pins

DDAn PORTAn I/O Pull-up Comment

0 0 Input No Tri-state (high-Z)

0 1 Input Yes PAn will source current if ext. pulled low

1 0 Output No Push-pull Zero Output

1 1 Output No Push-pull One Output

Note: n: 7,6…0, pin number.

Port A Schematics Note that all port pins are synchronized. The synchronization latch is, however, not

shown in the figure.

Figure 51. Port A Schematic Diagrams (Pins PA0 - PA7)

MOS PULLUP

PAn

TO ADC MUX

WRITE PORTA

WP:

WRITE DDRA

WD:

READ PORTA LATCH

RL:

READ PORTA PIN

RP:

READ DDRA

RD:

0-7

PWRDN

RESET

DDAn

RESET

PORTAn

DATA BUS

ADCn

1041H–11/01

Port B Port B is an 8-bit bi-directional I/O port.

Three I/O memory address locations are allocated for the Port B, one each for the Data Register – PORTB, $18($38), Data Direction Register – DDRB, $17($37) and the Port B Input Pins – PINB, $16($36). The Port B Input Pins address is read-only, while the Data Register and the Data Direction Register are read/write.

All port pins have individually selectable pull-up resistors. The Port B output buffers can sink 20 mA and thus drive LED displays directly. When pins PB0 to PB7 are used as inputs and are externally pulled low, they will source current if the internal pull-up resistors are activated.

The Port B pins with alternate functions are shown in Table 30.

Table 30. Port B Pin Alternate Functions

Port Pin Alternate Functions

PB0 T0 (Timer/Counter0 External Counter Input)

PB1 T1 (Timer/Counter1 External Counter Input)

PB2 AIN0 (Analog Comparator Positive Input)

PB3 AIN1 (Analog Comparator Negative Input)

Port B Data Register – PORTB

Port B Data Direction Register – DDRB

Port B Input Pins Address – PINB

PB4 SS

PB5 MOSI (SPI Bus Master Output/Slave Input)

PB6 MISO (SPI Bus Master Input/Slave Output)

PB7 SCK (SPI Bus Serial Clock)

(SPI Slave Select Input)

When the pins are used for the alternate function, the DDRB and PORTB registers have to be set according to the alternate function description.

Bit 76543210

$18 ($38)

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

$17 ($37) DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 DDRB

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

$16 ($36) PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB

Read/WriteRRRRRRRR

Initial Value N/A N/A N/A N/A N/A N/A N/A N/A

PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 PORTB

The Port B Input Pins address (PINB) is not a register and this address enables access to the physical value on each Port B pin. When reading PORTB, the Port B Data Latch is read and when reading PINB, the logical values present on the pins are read.

AT90S/LS8535

1041H–11/01

AT90S/LS8535

Port B As General Digital I/O All eight pins in Port B have equal functionality when used as digital I/O pins.

PBn, general I/O pin: The DDBn bit in the DDRB register selects the direction of this pin. If DDBn is set (one), PBn is configured as an output pin. If DDBn is cleared (zero), PBn is configured as an input pin. If PORTBn is set (one) when the pin is configured as an input pin, the MOS pull-up resistor is activated. To switch the pull-up resistor off, the PORTBn has to be cleared (zero) or the pin has to be configured as an output pin. The port pins are tri-stated when a reset condition becomes active, even if the clock is not running.

Table 31. DDBn Effects on Port B Pins

DDBn PORTBn I/O Pull-up Comment

0 0 Input No Tri-state (high-Z)

0 1 Input Yes PBn will source current if ext. pulled low

1 0 Output No Push-pull Zero Output

1 1 Output No Push-pull One Output

Note: n: 7,6…0, pin number.

Alternate Functions of Port B The alternate pin configuration is as follows:

• SCK – Port B, Bit 7

SCK: Master clock output, slave clock input pin for SPI channel. When the SPI is enabled as a slave, this pin is configured as an input regardless of the setting of DDB7. When the SPI is enabled as a master, the data direction of this pin is controlled by DDB7. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB7 bit. See the description of the SPI port for further details.

• MISO – Port B, Bit 6

MISO: Master data input, slave data output pin for SPI channel. When the SPI is enabled as a master, this pin is configured as an input regardless of the setting of DDB6. When the SPI is enabled as a slave, the data direction of this pin is controlled by DDB6. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB6 bit. See the description of the SPI port for further details.

• MOSI – Port B, Bit 5

MOSI: SPI Master data output, slave data input for SPI channel. When the SPI is enabled as a slave, this pin is configured as an input regardless of the setting of DDB5. When the SPI is enabled as a master, the data direction of this pin is controlled by DDB5. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB5 bit. See the description of the SPI port for further details.

– Port B, Bit 4

• SS

: Slave port select input. When the SPI is enabled as a slave, this pin is configured as an input regardless of the setting of DDB4. As a slave, the SPI is activated when this pin is driven low. When the SPI is enabled as a master, the data direction of this pin is controlled by DDB4. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB4 bit. See the description of the SPI port for further details.

• AIN1 – Port B, Bit 3

1041H–11/01

AIN1, Analog Comparator Negative Input. When configured as an input (DDB3 is cleared [zero]) and with the internal MOS pull-up resistor switched off (PB3 is cleared [zero]), this pin also serves as the negative input of the on-chip Analog Comparator. During Power-down mode, the Schmitt trigger of the digital input is disconnected. This

allows analog signals that are close to VCC/2 to be present during power-down without causing excessive power consumption.

• AIN0 – Port B, Bit 2

AIN0, Analog Comparator Positive Input. When configured as an input (DDB2 is cleared [zero]) and with the internal MOS pull-up resistor switched off (PB2 is cleared [zero]), this pin also serves as the positive input of the on-chip Analog Comparator. During Power-down mode, the Schmitt trigger of the digital input is disconnected. This allows analog signals that are close to V

/2 to be present during power-down without causing

excessive power consumption.

• T1 – Port B, Bit 1

T1, Timer/Counter1 counter source. See the timer description for further details.

• T0 – Port B, Bit 0

T0: Timer/Counter0 counter source. See the timer description for further details.

Port B Schematics Note that all port pins are synchronized. The synchronization latches are, however, not

shown in the figures.

Figure 52. Port B Schematic Diagram (Pins PB0 and PB1)

AT90S/LS8535

1041H–11/01

Figure 53. Port B Schematic Diagram (Pins PB2 and PB3)

MOS PULLUP

PBn

AT90S/LS8535

RESET

DDBn

RESET

PORTBn

DATA B US

WP:

WRITE PORTB

WD:

WRITE DDRB

RL:

READ PORTB LATCH

RP:

READ PORTB PIN

RD:

READ DDRB

2, 3

0, 1

PWRDN

Figure 54. Port B Schematic Diagram (Pin PB4)

MOS PULLUP

PB4

TO COMPARATOR

RESET

DDB4

RESET

PORTB4

AINm

DATA BUS

1041H–11/01

WRITE PORTB

WP:

WRITE DDRB

WD:

READ PORTB LATCH

RL:

READ PORTB PIN

RP:

READ DDRB

RD:

SPI MASTER ENABLE

MSTR:

SPI ENABLE

SPE:

MSTR SPE

SPI SS

Figure 55. Port B Schematic Diagram (Pin PB5)

MOS PULLUP

PB5

WRITE PORTB

WP:

WRITE DDRB

WD:

READ PORTB LATCH

RL:

READ PORTB PIN

RP:

READ DDRB

RD:

SPI ENABLE

SPE:

MASTER SELECT

MSTR

RESET

DDB5

RESET

PORTB5

MSTR SPE SPI MASTER

OUT

SPI SLAVE IN

DATA BUS

Figure 56. Port B Schematic Diagram (Pin PB6)

MOS PULLUP

PB6

WRITE PORTB

WP:

WRITE DDRB

WD:

READ PORTB LATCH

RL:

READ PORTB PIN

RP:

READ DDRB

RD:

SPI ENABLE

SPE:

MASTER SELECT

MSTR

RESET

DDB6

RESET

PORTB6

MSTR SPE SPI SLAVE

OUT

SPI MASTER IN

DATA B US

AT90S/LS8535

1041H–11/01

Figure 57. Port B Schematic Diagram (Pin PB7)

MOS PULLUP

PB7

WRITE PORTB

WP:

WRITE DDRB

WD:

READ PORTB LATCH

RL:

READ PORTB PIN

RP:

READ DDRB

RD:

SPI ENABLE

SPE:

MASTER SELECT

MSTR

AT90S/LS8535

RESET

DDB7

RESET

PORTB7

MSTR SPE SPI CLOCK

OUT

DATA BUS

SPI CLOCK IN

1041H–11/01

Port C Port C is an 8-bit bi-directional I/O port.

Three I/O memory address locations are allocated for the Port C, one each for the Data Register – PORTC, $15($35), Data Direction Register – DDRC, $14($34) and the Port C Input Pins – PINC, $13($33). The Port C Input Pins address is read-only, while the Data Register and the Data Direction Register are read/write.

All port pins have individually selectable pull-up resistors. The Port C output buffers can sink 20 mA and thus drive LED displays directly. When pins PC0 to PC7 are used as inputs and are externally pulled low, they will source current if the internal pull-up resistors are activated.

Port C Data Register – PORTC

Bit 76543210

PORTC7 PORTC6 PORTC5 PORTC4 PORTC3 PORTC2 PORTC1 PORTC0 PORTC

Port C Data Direction Register – DDRC

Port C Input Pins Address – PINC

$15 ($35)

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

$14 ($34) DDC7 DDC6 DDC5 DDC4 DDC3 DDC2 DDC1 DDC0 DDRC

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

$13 ($33) PINC7 PINC6 PINC5 PINC4 PINC3 PINC2 PINC1 PINC0 PINC

Read/WriteRRRRRRRR

Initial Value N/A N/A N/A N/A N/A N/A N/A N/A

The Port C Input Pins address (PINC) is not a register; this address enables access to the physical value on each Port C pin. When reading PORTC, the Port C Data Latch is read and when reading PINC, the logical values present on the pins are read.

Port C As General Digital I/O All eight pins in Port C have equal functionality when used as digital I/O pins.

PCn, general I/O pin: The DDCn bit in the DDRC register selects the direction of this pin. If DDCn is set (one), PCn is configured as an output pin. If DDCn is cleared (zero), PCn is configured as an input pin. If PORTCn is set (one) when the pin is configured as an input pin, the MOS pull-up resistor is activated. To switch the pull-up resistor off, PORTCn has to be cleared (zero) or the pin has to be configured as an output pin.The port pins are tri-stated when a reset condition becomes active, even if the clock is not running.

Table 32. DDCn Effects on Port C Pins

DDCn PORTCn I/O Pull-up Comment

0 0 Input No Tri-state (high-Z)

0 1 Input Yes PCn will source current if ext. pulled low

1 0 Output No Push-pull Zero Output

1 1 Output No Push-pull One Output

Note: n: 7…0, pin number

AT90S/LS8535

1041H–11/01

AT90S/LS8535

Alternate Functions of Port C When the AS2 bit in ASSR is set (one) to enable asynchronous clocking of

Timer/Counter2, pins PC6 and PC7 are disconnected from the port. In this mode, a crystal oscillator is connected to the pins and the pins cannot be used as I/O pins.

Port C Schematics Note that all port pins are synchronized. The synchronization latch is, however, not

shown in the figure.

Figure 58. Port C Schematic Diagram (Pins PC0 - PC5)

MOS PULLUP

PCn

RESET

DDCn

RESET

PORTCn

DATA B US

WP:

WRITE PORTC

WD:

WRITE DDRC

RL:

READ PORTC LATCH

RP:

READ PORTC PIN

RD:

READ DDRC

0-5

Figure 59. Port C Schematic Diagram (Pins PC6)

MOS PULLUP

PC6

RESET

DDC6

RESET

PORTC6

DATA B US

1041H–11/01

WP:

WRITE PORTC

WD:

WRITE DDRC

RL:

READ PORTC LATCH

RP:

READ PORTC PIN

RD:

READ DDRC

AS2:

ASYNCH SELECT T/C2

AS2 T/C2 OSC

AMP INPU

Figure 60. Port C Schematic Diagram (Pins PC7)

Port D Port D is an 8-bit bi-directional I/O port with internal pull-up resistors.

Three I/O memory address locations are allocated for Port D, one each for the Data Register – PORTD, $12($32), Data Direction Register – DDRD, $11($31) and the Port D Input Pins – PIND, $10($30). The Port D Input Pins address is read-only, while the Data Register and the Data Direction Register are read/write.

The Port D output buffers can sink 20 mA. As inputs, Port D pins that are externally pulled low will source current if the pull-up resistors are activated. Some Port D pins have alternate functions as shown in Table 33.

Table 33. Port D Pin Alternate Functions

Port Pin Alternate Function

PD0 RXD (UART Input line)

PD1 TXD (UART Output line)

PD2 INT0 (External interrupt 0 input)

PD3 INT1 (External interrupt 1 input)

PD4 OC1B (Timer/Counter1 output compareB match output)

PD5 OC1A (Timer/Counter1 output compareA match output)

PD6 ICP (Timer/Counter1 input capture pin)

PD7 OC2 (Timer/Counter2 output compare match output)

AT90S/LS8535

1041H–11/01

Port D Data Register – PORTD

Port D Data Direction Register – DDRD

Port D Input Pins Address – PIND

AT90S/LS8535

Bit 76543210

$12 ($32)

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

$11 ($31) DDD7 DDD6 DDD5 DDD4 DDD3 DDD2 DDD1 DDD0 DDRD

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

$10 ($30) PIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 PIND

Read/WriteRRRRRRRR

Initial Value N/A N/A N/A N/A N/A N/A N/A N/A

The Port D Input Pins address (PIND) is not a register; this address enables access to the physical value on each Port D pin. When reading PORTD, the Port D Data Latch is read and when reading PIND, the logical values present on the pins are read.

PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 PORTD

Port D As General Digital I/O PDn, general I/O pin: The DDDn bit in the DDRD register selects the direction of this pin.

If DDDn is set (one), PDn is configured as an output pin. If DDDn is cleared (zero), PDn is configured as an input pin. If PDn is set (one) when configured as an input pin, the MOS pull-up resistor is activated. To switch the pull-up resistor off, the PDn has to be cleared (zero) or the pin has to be configured as an output pin.The port pins are tristated when a reset condition becomes active, even if the clock is not running.

Table 34. DDDn Bits on Port D Pins

DDDn PORTDn I/O Pull-up Comment

0 0 Input No Tri-state (high-Z)

0 1 Input Yes PDn will source current if ext. pulled low

1 0 Output No Push-pull Zero Output

1 1 Output No Push-pull One Output

Note: n: 7,6…0, pin number.

Alternate Functions of Port D • OC2 – Port D, Bit 7

OC2, Timer/Counter2 output compare match output: The PD7 pin can serve as an external output for the Timer/Counter2 output compare. The pin has to be configured as an output (DDD7 set [one]) to serve this function. See the timer description on how to enable this function. The OC2 pin is also the output pin for the PWM mode timer function.

• ICP – Port D, Bit 6

1041H–11/01

ICP – Input Capture Pin: The PD6 pin can act as an input capture pin for Timer/Counter1. The pin has to be configured as an input (DDD6 cleared [zero]) to serve this function. See the timer description on how to enable this function.

• OC1A – Port D, Bit 5

OC1A, Output compare matchA output: The PD5 pin can serve as an external output for the Timer/Counter1 output compareA. The pin has to be configured as an output (DDD5 set [one]) to serve this function. See the timer description on how to enable this function. The OC1A pin is also the output pin for the PWM mode timer function.

• OC1B – Port D, Bit 4

OC1B, Output compare matchB output: The PD4 pin can serve as an external output for the Timer/Counter1 output compareB. The pin has to be configured as an output (DDD4 set [one]) to serve this function. See the timer description on how to enable this function. The OC1B pin is also the output pin for the PWM mode timer function.

• INT1 – Port D, Bit 3

INT1, External Interrupt source 1: The PD3 pin can serve as an external interrupt source to the MCU. See the interrupt description for further details and how to enable the source.

• INT0 – Port D, Bit 2

INT0, External Interrupt source 0: The PD2 pin can serve as an external interrupt source to the MCU. See the interrupt description for further details and how to enable the source.

• TXD – Port D, Bit 1

Transmit Data (data output pin for the UART). When the UART Transmitter is enabled, this pin is configured as an output, regardless of the value of DDD1.

• RXD – Port D, Bit 0

Receive Data (data input pin for the UART). When the UART Receiver is enabled, this pin is configured as an input, regardless of the value of DDD0. When the UART forces this pin to be an input, a logical “1” in PORTD0 will turn on the internal pull-up.

AT90S/LS8535

1041H–11/01

AT90S/LS8535

Port D Schematics Note that all port pins are synchronized. The synchronization latches are, however, not

shown in the figures.

Figure 61. Port D Schematic Diagram (Pin PD0)

MOS PULLUP

PD0

RESET

DDD0

RESET

PORTD0

DATA BUS

WRITE PORTD

WP:

WRITE DDRD

WD:

READ PORTD LATCH

RL:

READ PORTD PIN

RP:

READ DDRD

RD:

UART RECEIVE DATA

RXD:

UART RECEIVE ENABLE

RXEN:

Figure 62. Port D Schematic Diagram (Pin PD1)

MOS PULLUP

PD1

RXEN

RXD

RESET

DDD1

RESET

PORTD1

DATA BUS

1041H–11/01

WRITE PORTD

WP:

WRITE DDRD

WD:

READ PORTD LATCH

RL:

READ PORTD PIN

RP:

READ DDRD

RD:

UART TRANSMIT DATA

TXD:

UART TRANSMIT ENABLE

TXEN:

TXEN

TXD

Figure 63. Port D Schematic Diagram (Pins PD2 and PD3)

Figure 64. Port D Schematic Diagram (Pins PD4 and PD5)

AT90S/LS8535

1041H–11/01

Figure 65. Port D Schematic Diagram (Pin PD6)

MOS PULLUP

PD6

AT90S/LS8535

RESET

DDD6

RESET

PORTD6

DATA BUS

WP:

WRITE PORTD

WD:

WRITE DDRD

RL:

READ PORTD LATCH

RP:

READ PORTD PIN

RD:

READ DDRD

ACIC:

COMPARATOR IC ENABLE

ACO:

COMPARATOR OUTPUT

NOISE CANCELER EDGE SELECT ICF1

ICNC1 ICES1

Figure 66. Port D Schematic Diagram (Pin PD7)

ACIC ACO

1041H–11/01

Memory Programming

Program and Data Memory Lock Bits

The AT90S8535 MCU provides two Lock bits that can be left unprogrammed (“1”) or can be programmed (“0”) to obtain the additional features listed in Table 35. The Lock bits can only be erased with the Chip Erase command.

Table 35. Lock Bit Protection Modes

Memory Lock Bits

Protection TypeMode LB1 LB2

1 1 1 No memory lock features enabled.

2 0 1 Further programming of the Flash and EEPROM is disabled.

3 0 0 Same as mode 2 and verify is also disabled.

Note: 1. In Parallel Mode, further programming of the Fuse bits is also disabled. Program the

Fuse bits before programming the Lock bits.

Fuse Bits The AT90S8535 has two Fuse bits, SPIEN and FSTRT.

• When the SPIEN Fuse is programmed (“0”), Serial Program and Data Downloading

is enabled. Default value is programmed (“0”). The SPIEN Fuse is not accessible in Serial Programming Mode.

• When the FSTRT Fuse is programmed (“0”), the short start-up time is selected.

Default value is unprogrammed (“1”).

The status of the Fuse bits is not affected by Chip Erase.

(1)

Signature Bytes All Atmel microcontrollers have a three-byte signature code that identifies the device.

and Parallel modes. The three bytes reside in a

Programming the Flash and EEPROM

This code can be read in both Serial separate address space.

1. $000: $1E (indicates manufactured by Atmel)

2. $001: $93 (indicates 8K bytes Flash memory)

3. $002: $03 (indicates AT90S8535 device when signature byte $001 is $93)

Note: 1. When both Lock bits are programmed (lock mode 3), the signature bytes cannot be

read in Serial Mode. Reading the signature bytes will return: $00, $01 and $02.

Atmel’s AT90S8535 offers 8K bytes of in-system reprogrammable Flash program memory and 512 bytes of EEPROM data memory.

The AT90S8535 is shipped with the On-chip Flash program and EEPROM data memory arrays in the erased state (i.e., contents = $FF) and ready to be programmed. This device supports a high-voltage (12V) Parallel Programming Mode and a low-voltage Serial Programming Mode. The +12V is used for programming enable only and no current of significance is drawn by this pin. The Serial Programming Mode provides a convenient way to download program and data into the AT90S8535 inside the user’s system.

The program and data memory arrays on the AT90S8535 are programmed byte-by-byte in either programming mode. For the EEPROM, an auto-erase cycle is provided within the self-timed write instruction in the Serial Programming Mode.

During programming, the supply voltage must be in accordance with Table 36.

AT90S/LS8535

1041H–11/01

AT90S/LS8535

Table 36. Supply Voltage during Programming

Part Serial Programming Parallel Programming

AT90S8535 4.0 - 6.0V 4.5 - 5.5V

AT90LS8535 2.7 - 6.0V 4.5 - 5.5V

Parallel Programming This section describes how to parallel program and verify Flash program memory,

EEPROM data memory, Lock bits and Fuse bits in the AT90S8535.

Signal Names In this section, some pins of the AT90S8535 are referenced by signal names describing

their function during parallel programming. See Figure 67 and Table 37. Pins not described in Table 37 are referenced by pin name.

The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse. The bit coding are shown in Table 38.

When pulsing WR

or OE, the command loaded determines the action executed. The

command is a byte where the different bits are assigned functions as shown in Table 39.

Figure 67. Parallel Programming

RDY/BSY

XA0

XA1

+12 V

PD1

PD2

PD3

PD4

PD5

PD6

RESET

XTAL1

GND

AT90S8535

VCC

PB7 - PB0 DATA

+5V

1041H–11/01

Table 37. Pin Name Mapping

Signal Name in

Programming Mode Pin Name I/O Function

RDY/BSY PD1 O

BS PD4 I

XA0 PD5 I XTAL Action Bit 0

XA1 PD6 I XTAL Action Bit 1

DATA PB7 - 0 I/O Bi-directional Data Bus (Output when OE

PD2 I Output Enable (Active low)

PD3 I Write Pulse (Active low)

0: Device is busy programming, 1: Device is ready for new command

Byte Select (“0” selects low byte, “1” selects high byte)

is low)

Table 38. XA1 and XA0 Coding

XA1 XA0 Action when XTAL1 is Pulsed

0 0 Load Flash or EEPROM Address (high or low address byte determined by BS)

0 1 Load Data (High or low data byte for Flash determined by BS)

1 0 Load Command

1 1 No Action, Idle

Table 39. Command Byte Bit Coding

Command Byte Command Executed

1000 0000 Chip Erase

0100 0000 Write Fuse Bits

0010 0000 Write Lock Bits

0001 0000 Write Flash

0001 0001 Write EEPROM

0000 1000 Read Signature Bytes

0000 0100 Read Lock and Fuse Bits

0000 0010 Read Flash

0000 0011 Read EEPROM

Enter Programming Mode The following algorithm puts the device in Parallel Programming Mode:

1. Apply supply voltage according to Table 36, between V

and GND.

2. Set the RESET and BS pin to “0” and wait at least 100 ns.

3. Apply 11.5 - 12.5V to RESET. Any activity on BS within 100 ns after +12V has

been applied to RESET

, will cause the device to fail entering programming mode.

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1041H–11/01

AT90S/LS8535

Chip Erase The Chip Erase command will erase the Flash and EEPROM memories and the Lock

bits. The Lock bits are not reset until the Flash and EEPROM have been completely erased. The Fuse bits are not changed. Chip Erase must be performed before the Flash or EEPROM is reprogrammed.

Load Command “Chip Erase”:

1. Set XA1, XA0 to “10”. This enables command loading.

2. Set BS to “0”.

3. Set DATA to “1000 0000”. This is the command for Chip Erase.

4. Give XTAL1 a positive pulse. This loads the command.

WLWH_CE

a t

WLWH_CE

value. Chip Erase does not generate any activity on the RDY/BSY

5. Give WR

for pin.

Programming the Flash A: Load Command “Write Flash”

1. Set XA1, XA0 to “10”. This enables command loading.

2. Set BS to “0”.

3. Set DATA to “0001 0000”. This is the command for Write Flash.

4. Give XTAL1 a positive pulse. This loads the command.

-wide negative pulse to execute Chip Erase. See Table 40

B: Load Address High Byte

1. Set XA1, XA0 to “00”. This enables address loading.

2. Set BS to “1”. This selects high byte.

3. Set DATA = Address high byte ($00 - $0F).

4. Give XTAL1 a positive pulse. This loads the address high byte.

C: Load Address Low Byte

1. Set XA1, XA0 to “00”. This enables address loading.

2. Set BS to “0”. This selects low byte.

3. Set DATA = Address low byte ($00 - $FF).

4. Give XTAL1 a positive pulse. This loads the address low byte.

D: Load Data Low Byte

1. Set XA1, XA0 to “01”. This enables data loading.

2. Set DATA = Data low byte ($00 - $FF).

3. Give XTAL1 a positive pulse. This loads the data low byte.

E: Write Data Low Byte

1. Set BS to “0”. This selects low data.

2. Give WR

a negative pulse. This starts programming of the data byte. RDY/BSY

goes low.

3. Wait until RDY/BSY

goes high to program the next byte.

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(See Figure 68 for signal waveforms.)

F: Load Data High Byte

1. Set XA1, XA0 to “01”. This enables data loading.

2. Set DATA = Data high byte ($00 - $FF).

3. Give XTAL1 a positive pulse. This loads the data high byte.

G: Write Data High Byte

1. Set BS to “1”. This selects high data.

2. Give WR a negative pulse. This starts programming of the data byte. RDY/BSY

goes low.

3. Wait until RDY/BSY

goes high to program the next byte.

(See Figure 69 for signal waveforms.)

The loaded command and address are retained in the device during programming. For efficient programming, the following should be considered:

• The command needs only be loaded once when writing or reading multiple memory

locations.

• Address high byte needs only be loaded before programming a new 256-word page

in the Flash.

• Skip writing the data value $FF, that is, the contents of the entire Flash and EEPROM

after a Chip Erase.

These considerations also apply to EEPROM programming and Flash, EEPROM and signature byte reading.

Figure 68. Programming the Flash Waveforms

DATA

XA1

XA0

XTAL1

RDY/BSY

RESET

$10 ADDR. HIGH ADDR. LOW DATA LOW

12V

AT90S/LS8535

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Figure 69. Programming the Flash Waveforms (Continued)

AT90S/LS8535

DATA

XA1

XA0

XTAL1

RDY/BSY

RESET

DATA HIGH

+12V

Reading the Flash The algorithm for reading the Flash memory is as follows (refer to “Programming the

Flash” for details on command and address loading):

1. A: Load Command “0000 0010”.

2. B: Load Address High Byte ($00 - $0F).

3. C: Load Address Low Byte ($00 - $FF).

4. Set OE

to “0” and BS to “0”. The Flash word low byte can now be read at DATA.

5. Set BS to “1”. The Flash word high byte can now be read from DATA.

6. Set OE to “1”.

Programming the EEPROM The programming algorithm for the EEPROM data memory is as follows (refer to “Pro-

gramming the Flash” for details on command, address and data loading):

1. A: Load Command “0001 0001”.

2. B: Load Address High Byte ($00 - $01).

3. C: Load Address Low Byte ($00 - $FF).

4. D: Load Data Low Byte ($00 - $FF).

5. E: Write Data Low Byte.

Reading the EEPROM The algorithm for reading the EEPROM memory is as follows (refer to “Programming the

Flash” for details on command and address loading):

1. A: Load Command “0000 0011”.

2. B: Load Address High Byte ($00 - $01).

3. C: Load Address Low Byte ($00 - $FF).

4. Set OE

to “0” and BS to “0”. The EEPROM data byte can now be read at DATA.

5. Set OE to “1”.

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Programming the Fuse Bits The algorithm for programming the Fuse bits is as follows (refer to “Programming the

Flash” for details on command and data loading):

1. A: Load Command “0100 0000”.

2. D: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.

Bit 5 = SPIEN Fuse bit. Bit 0 = FSTRT Fuse bit. Bit 7-6,4-1 = “1”. These bits are reserved and should be left unprogrammed (“1”).

3. Give WR

a t

WLWH_PFB

-wide negative pulse to execute the programming, t

WLWH_PFB

is found in Table 40. Programming the Fuse bits does not generate any activity on the RDY/BSY

pin.

Programming the Lock Bits The algorithm for programming the Lock bits is as follows (refer to “Programming the

Flash” on page 95 for details on command and data loading):

1. A: Load Command “0010 0000”.

2. D: Load Data Low Byte. Bit n = “0” programs the Lock bit.

Bit 2 = Lock Bit2 Bit 1 = Lock Bit1 Bit 7-3,0 = “1”. These bits are reserved and should be left unprogrammed (“1”).

3. E: Write Data Low Byte.

The Lock bits can only be cleared by executing Chip Erase.

Reading the Fuse and Lock Bits

The algorithm for reading the Fuse and Lock bits is as follows (refer to “Programming the Flash” on page 95 for details on command loading):

1. A: Load Command “0000 0100”.

2. Set OE

to “0” and BS to “1”. The status of the Fuse and Lock bits can now be read at DATA (“0” means programmed). Bit 7 = Lock Bit1 Bit 6 = Lock Bit2 Bit 5 = SPIEN Fuse bit Bit 0 = FSTRT Fuse bit

3. Set OE

to “1”. Observe that BS needs to be set to “1”.

Reading the Signature Bytes The algorithm for reading the signature bytes is as follows (refer to “Programming the

Flash” on page 95 for details on command and address loading):

1. A: Load Command “0000 1000”.

2. C: Load Address Low Byte ($00 - $02). Set OE

to “0” and BS to “0”. The selected signature byte can now be read at DATA.

3. Set OE to “1”.

AT90S/LS8535

1041H–11/01

AT90S/LS8535

Parallel Programming Characteristics

Figure 70. Parallel Programming Timing

XLWL

XTAL1

Data & Contol

(DATA, XA0/1, BS)

RDY/BSY

DATA

Table 40. Parallel Programming Characteristics, T

Symbol Parameter Min Typ Max Units

DVXH

XHXL

XLDX

XLWL

BVWL

RHBX

WLWH

WHRL

WLRH

XLOL

OLDV

OHDZ

WLWH_CE

WLWH_PFB

Notes: 1. Use t

Programming Enable Voltage 11.5 12.5 V

Programming Enable Current 250.0 µA

Data and Control Setup before XTAL1 High 67.0 ns

XTAL1 Pulse Width High 67.0 ns

Data and Control Hold after XTAL1 Low 67.0 ns

XTAL1 Low to WR Low 67.0 ns

BS Valid to WR Low 67.0 ns

BS Hold after RDY/BSY High 67.0 ns

WR Pulse Width Low

WR High to RDY/BSY Low

WR Low to RDY/BSY High

XTAL1 Low to OE Low 67.0 ns

OE Low to DATA Valid 20.0 ns

OE High to DATA Tri-stated 20.0 ns

WR Pulse Width Low for Chip Erase 5.0 10.0 15.0 ms

WR Pulse Width Low for Programming the Fuse Bits 1.0 1.5 1.8 ms

WLWH_CE

2. If t

is held longer than t

WLWH

XHXL

DVXH

for Chip Erase and t

XLDX

XLOL

(1)

(2)

WLRH

BVWL

WLWH

WHRL

OLDV

= 25°C ± 10%, VCC = 5V ± 10%

67.0 ns

20.0 ns

0.5 0.7 0.9 ms

WLWH_PFB

for programming the Fuse bits.

, no RDY/BSY pulse will be seen.

RHBX

WLRH

OHDZ

Write

Read

Serial Downloading Both the Flash and EEPROM memory arrays can be programmed using the serial SPI

bus while RESET (input) and MISO (output), see Figure 71. After RESET Enable instruction needs to be executed first before program/erase operations can be executed.

1041H–11/01

is pulled to GND. The serial interface consists of pins SCK, MOSI

is set low, the Programming

Figure 71. Serial Programming and Verify

PB7 PB6 PB5

2.7 - 6.0V

SCK MISO MOSI

GND

CLOCK INPUT

RESET

XTAL1

GND

AT90S8535

VCC

For the EEPROM, an auto-erase cycle is provided within the self-timed write instruction and there is no need to first execute the Chip Erase instruction. The Chip Erase instruction turns the content of every memory location in both the program and EEPROM arrays into $FF.

The program and EEPROM memory arrays have separate address spaces: $0000 to $0FFF for program memory and $0000 to $01FF for EEPROM memory.

Either an external clock is supplied at pin XTAL1 or a crystal needs to be connected across pins XTAL1 and XTAL2. The minimum low and high periods for the serial clock (SCK) input are defined as follows:

Serial Programming Algorithm

Low: > 2 XTAL1 clock cycles

High: > 2 XTAL1 clock cycles

When writing serial data to the AT90S8535, data is clocked on the rising edge of SCK.

When reading data from the AT90S8535, data is clocked on the falling edge of SCK. See Figure 72, Figure 73 and Table 43 for timing details.

To program and verify the AT90SS8535 in the Serial Programming Mode, the following sequence is recommended (see 4-byte instruction formats in Table 42

1. Power-up sequence: Apply power between V

and GND while RESET and SCK are set to “0”. If a crys-

tal is not connected across pins XTAL1 and XTAL2, apply a clock signal to the XTAL1 pin. In some systems, the programmer cannot guarantee that SCK is held low during power-up. In this case, RESET

must be given a positive pulse of at least

two XTAL1 cycles duration after SCK has been set to “0”.

2. Wait for at least 20 ms and enable serial programming by sending the Programming Enable serial instruction to the MOSI (PB5) pin.

3. The serial programming instructions will not work if the communication is out of synchronization. When in sync, the second byte ($53) will echo back when issuing the third byte of the Programming Enable instruction. Whether the echo is correct or not, all four bytes of the instruction must be transmitted. If the $53 did not echo back, give SCK a positive pulse and issue a new Programming Enable instruction. If the $53 is not seen within 32 attempts, there is no functional device connected.

100

AT90S/LS8535

1041H–11/01

Rainbow Electronics AT90LS8535 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Features

Pin Configurations

Description The AT90S8535 is a low-power CMOS 8-bit microcontroller based on the AVR RISC

Block Diagram Figure 1. The AT90S8535 Block Diagram

Pin Descriptions

Port A (PA7..PA0) Port A is an 8-bit bi-directional I/O port. Port pins can provide internal pull-up resistors

Port B (PB7..PB0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port B output

Port C (PC7..PC0) Port C is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port C output

Port D (PD7..PD0) Port D is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port D output

RESET

XTAL1 Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2 Output from the inverting oscillator amplifier.

AVCC AVCC is the supply voltage pin for Port A and the A/D Converter. If the ADC is not used,

AREF AREF is the analog reference input for the A/D Converter. For ADC operations, a volt-

AGND Analog ground. If the board has a separate analog ground plane, this pin should be con-

Clock Options

Crystal Oscillator XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can

External Clock To drive the device from an external clock source, XTAL2 should be left unconnected

Timer Oscillator For the Timer Oscillator pins, TOSC1 and TOSC2, the crystal is connected directly

Architectural Overview

General-purpose Register File

ALU – Arithmetic Logic Unit

In-System Programmable Flash Program Memory

SRAM Data Memory Figure 8 shows how the AT90S8535 SRAM memory is organized.

Program and Data Addressing Modes

Register Direct, Single Register Rd

Register Direct, Two Registers Rd And Rr

I/O Direct Figure 11. I/O Direct Addressing

Data Direct Figure 12. Direct Data Addressing

Figure 13. Data Indirect with Displacement

Data Indirect Figure 14. Data Indirect Addressing

Constant Addressing Using the LPM Instruction

Indirect Program Addressing, IJMP and ICALL

Relative Program Addressing, RJMP and RCALL

EEPROM Data Memory The AT90S8535 contains 512 bytes of data EEPROM memory. It is organized as a sep-

Memory Access Times and Instruction Execution Timing

I/O Memory The I/O space definition of the AT90S8535 is shown in Table 1.

Status Register – SREG The AVR Status Register (SREG) at I/O space location $3F ($5F) is defined as:

Stack Pointer – SP The AT90S8535 Stack Pointer is implemented as two 8-bit registers in the I/O space

Reset and Interrupt Handling

Reset Sources The AT90S8535 has three sources of reset:

Power-on Reset A Power-on Reset (POR) circuit ensures that the device is reset from power-on. As

External Reset An external reset is generated by a low level on the RESET

Watchdog Reset When the Watchdog times out, it will generate a short reset pulse of 1 XTAL cycle dura-

MCU Status Register – MCUSR

Interrupt Handling The AT90S8535 has two 8-bit interrupt mask control registers: GIMSK (General Inter-

General Interrupt Mask Register – GIMSK

General Interrupt Flag Register – GIFR

Timer/Counter Interrupt Mask Register – TIMSK

Timer/Counter Interrupt Flag Register – TIFR

External Interrupts The external interrupts are triggered by the INT1 and INT0 pins. Observe that, if

Interrupt Response Time The interrupt execution response for all the enabled AVR interrupts is four clock cycles

MCU Control Register – MCUCR

Sleep Modes To enter any of the three sleep modes, the SE bit in MCUCR must be set (one) and a

Idle Mode When the SM1/SM0 bits are set to 00, the SLEEP instruction makes the MCU enter the

Power-down Mode When the SM1/SM0 bits are set to 10, the SLEEP instruction makes the MCU enter the

Power Save Mode When the SM1/SM0 bits are 11, the SLEEP instruction makes the MCU enter the Power

Timer/Counters The AT90S8535 provides three general-purpose Timer/Counters – two 8-bit T/Cs and

Timer/Counter Prescalers

8-bit Timer/Counter0 Figure 30 shows the block diagram for Timer/Counter0.

Timer/Counter0 Control Register – TCCR0

Timer Counter 0 – TCNT0

16-bit Timer/Counter1 Figure 31 shows the block diagram for Timer/Counter1.

Timer/Counter1 Control Register A – TCCR1A

Timer/Counter1 Control Register B – TCCR1B

Timer/Counter1 – TCNT1H AND TCNT1L

Timer/Counter1 Output Compare Register – OCR1AH AND OCR1AL

Timer/Counter1 Output Compare Register – OCR1BH AND OCR1BL

Timer/Counter1 Input Capture Register – ICR1H AND ICR1L

Timer/Counter1 In PWM Mode When the PWM mode is selected, Timer/Counter1, the Output Compare Register1A

8-bit Timer/Counter2 Figure 34 shows the block diagram for Timer/Counter2.

Timer/Counter2 Control Register – TCCR2

Timer/Counter2 – TCNT2

Timer/Counter2 Output Compare Register – OCR2

Timer/Counter2 in PWM Mode When the PWM mode is selected, Timer/Counter2 and the Output Compare Register

Asynchronous Status Register – ASSR