Rainbow Electronics ATtiny28L User Manual

Features

• Utilizes the AVR

• AVR – High-performance and Low-power RISC Architecture

– 90 Powerful Instructions – Most Single Clock Cycle Execution – 32 x 8 General-purpose Working Registers – Up to 4 MIPS Throughput at 4 MHz

• Nonvolatile Program Memory

– 2K Bytes of Flash Program Memory – Endurance: 1,000 Write/Erase Cycles – Programming Lock for Flash Program Data Security

• Peripheral Features

– Interrupt and Wake-up on Low-level Input – One 8-bit Timer/Counter with Separate Prescaler – On-chip Analog Comparator – Programmable Watchdog Timer with On-chip Oscillator – Built-in High-current LED Driver with Programmable Modulation

• Special Microcontroller Features

– Low-power Idle and Power-down Modes – External and Internal Interrupt Sources – Power-on Reset Circuit with Programmable Start-up Time – Internal Calibrated RC Oscillator

• Power Consumption at 1 MHz, 2V, 25°C

– Active: 3.0 mA – Idle Mode: 1.2 mA – Power-down Mode: <1 µA

• I/O and Packages

– 11 Programmable I/O Lines, 8 Input Lines and a High-current LED Driver – 28-lead PDIP, 32-lead TQFP, and 32-pad MLF

• Operating Voltages

–V

: 1.8V - 5.5V for the ATtiny28V

: 2.7V - 5.5V for the ATtiny28L

–V

• Speed Grades

– 0 - 1.2 MHz for the ATtiny28V – 0 - 4 MHz For the ATtiny28L

RISC Architecture

8-bit Microcontroller with 2K Bytes of Flash

ATtiny28L ATtiny28V

Pin Configurations

PDIP

RESET

XTAL1 XTAL2

(AIN0) PB0

PD0 PD1 PD2 PD3 PD4

VCC

GND

PD5 PD6 PD7

1 2 3 4 5 6 7 8 9 10 11 12 13 14

28 27 26 25 24 23 22 21 20 19 18 17 16 15

PA0 PA1 PA3 PA2 (IR) PB7 PB6 GND NC VCC PB5 PB4 (INT1) PB3 (INT0) PB2 (T0) PB1 (AIN1)

PD3 PD4

VCC

GND

NC XTAL1 XTAL2

TQFP/MLF

PD2

PD1

32313029282726

1 2 3 4 5 6 7 8

9101112131415

PD5

PD6

PD0

RESET

PD7

(AIN0) PB0

PA0

PA1

PA3

(T0) PB2

(INT0) PB3

(AIN1) PB1

PA2 (IR)

24 23 22 21 20 19 18 17

(INT1) PB4

PB7 PB6 NC GND NC NC VCC PB5

Rev. 1062E–10/01

Description The ATtiny28 is a low-power CMOS 8-bit microcontroller based on the AVR RISC archi-

tecture. By executing powerful instructions in a single clock cycle, the ATtiny28 achieves throughputs approaching 1 MIPS per MHz, allowing the system designer to optimize power consumption versus processing speed. 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.

Block Diagram Figure 1. The ATtiny28 Block Diagram

VCC

GND

PROGRAM COUNTER

PROGRAM

FLASH

INSTRUCTION

DECODER

CONTROL

LINES

PROGRAMMING

LOGIC

DATA REGISTER

ANALOG

COMPARATOR

PORTB

STACK

POINTER

HARDWARE

STACK

GENERAL PURPOSE

REGISTERS

STATUS

PORTB

8-BIT DATA BUS

ALU

INTERNAL

OSCILLATOR

WATCHDOG

MCU CONTROL

TIMER/

COUNTER

INTERRUPT

DATA REGISTER

PORTD

TIMER

UNIT

PORTD

OSCILLATOR

TIMING AND

CONTROL

DATA DIR

REG. PORTD

XTAL2XTAL1

INTERNAL CALIBRATED OSCILLATOR

HARDWARE

MODULATOR

DATA REGISTER

PORTA

PORTA CONTROL

RESET

The ATtiny28 provides the following features: 2K bytes of Flash, 11 general-purpose I/O lines, 8 input lines, a high-current LED driver, 32 general-purpose working registers, an 8-bit timer/counter, internal and external interrupts, programmable Watchdog Timer with internal oscillator and 2 software-selectable power-saving modes. The Idle Mode stops the CPU while allowing the timer/counter 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. The wake-up or inter-

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rupt on low-level input feature enables the ATtiny28 to be highly responsive to external events, still featuring the lowest power consumption while in the power-down modes.

The device is manufactured using Atmel’s high-density, nonvolatile memory technology. By combining an enhanced RISC 8-bit CPU with Flash on a monolithic chip, the Atmel ATtiny28 is a powerful microcontroller that provides a highly flexible and cost-effective solution to many embedded control applications. The ATtiny28 AVR is supported with a full suite of program and system development tools including: macro assemblers, program debugger/simulators, in-circuit emulators and evaluation kits.

Pin Descriptions

VCC Supply voltage pin.

GND Ground pin.

Port A (PA3..PA0) Port A is a 4-bit I/O port. PA2 is output-only and can be used as a high-current LED

driver. At V bi-directional I/O pins with internal pull-ups (selected for each bit). The port pins are tristated when a reset condition becomes active, even if the clock is not running.

= 2.0V, the PA2 output buffer can sink 25 mA. PA3, PA1 and PA0 are

Port B (PB7..PB0) Port B is an 8-bit input port with internal pull-ups (selected for all Port B pins). Port B

pins that are externally pulled low will source current if the pull-ups are activated.

Port B also serves the functions of various special features of the ATtiny28 as listed on page 39. If any of the special features are enabled, the pull-up(s) on the corresponding pin(s) is automatically disabled. The port 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 I/O port. Port pins can provide internal pull-up resistors (selected for

each bit). The port pins are tri-stated when a reset condition becomes active, even if the clock is not running.

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

XTAL2 Output from the inverting oscillator amplifier.

RESET

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.

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Clock Options The device has the following clock source options, selectable by Flash Fuse bits as

shown in Table 1.

Table 1. Device Clocking Option Select

Clock Option CKSEL3..0

External Crystal/Ceramic Resonator 1111 - 1010

External Low-frequency Crystal 1001 - 1000

External RC Oscillator 0111 - 0101

Internal RC Oscillator 0100 - 0010

External Clock 0001 - 0000

Note: “1” means unprogrammed, “0” means programmed.

The various choices for each clocking option give different start-up times as shown in Table 5 on page 14.

Internal RC Oscillator The internal RC oscillator option is an on-chip calibrated oscillator running at a nominal

frequency of 1.2 MHz. If selected, the device can operate with no external components. The device is shipped with this option selected.

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. When the INTCAP fuse is programmed, internal load capacitors with typical values 50 pF are connected between XTAL1/XTAL2 and ground.

Figure 2. Oscillator Connections

MAX 1 HC BUFFER

Note: 1. When using the MCU oscillator as a clock for an external device, an HC buffer should

be connected as indicated in the figure.

XTAL2

XTAL1

GND

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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

EXTERNAL

OSCILLATOR

SIGNAL

XTAL2

XTAL1

GND

External RC Oscillator For timing insensitive applications, the external RC configuration shown in Figure 4 can

be used. For details on how to choose R and C, see Table 25 on page 54.

Figure 4. External RC Configuration

XTAL2

XTAL1

GND

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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 ALU (Arithmetic Logic Unit) 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.

Two of the 32 registers can be used as a 16-bit pointer for indirect memory access. This pointer is called the Z-pointer and can address the register file and the Flash program memory.

Figure 5. The ATtiny28 AVR RISC Architecture

Data Bus 8-bit

1K x 16

Program

Flash

Instruction

Decoder

Control Lines

Program

Counter

Status

and Test

32 x 8 General Purpose

Registrers

ALU

Control

Registrers

Interrupts

Unit

8-bit

Timer/Counter

Watchdog

Timer

Analog

Comparator

I/O Lines

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 5 shows the ATtiny28 AVR RISC microcontroller architecture. The AVR uses a Harvard architecture concept – with separate memories and buses for program and data memories. The program memory is accessed 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 every clock cycle. The program memory is reprogrammable Flash memory.

With the relative jump and relative call instructions, the whole 1K address space is directly accessed. All AVR instructions have a single 16-bit word format, meaning that every program memory address contains a single 16-bit instruction.

During interrupts and subroutine calls, the return address program counter (PC) is stored on the stack. The stack is a 3-level-deep hardware stack dedicated for subroutines and interrupts.

The I/O memory space contains 64 addresses for CPU peripheral functions such as Control Registers, Timer/Counters and other I/O functions. The memory spaces in the AVR architecture are all linear and regular memory maps.

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 sepa-

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rate interrupt vector in the interrupt vector table at the beginning of the program 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 registers in the CPU.

Figure 6. AVR

CPU General-purpose Working Registers

General …

Purpose …

Working R28

Registers R29

R30 (Z-Register low byte)

R31(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 are 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, OR and all other operations between two registers or on a single register apply to the entire register file.

Registers 30 and 31 form a 16-bit pointer (the Z-pointer), which is used for indirect Flash memory and register file access. When the register file is accessed, the contents of R31 are discarded by the CPU.

ALU – Arithmetic Logic Unit

Downloadable Flash Program Memory

Program and Data Addressing Modes

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, logic and bit functions. Some microcontrollers in the AVR product family feature a hardware multiplier in the arithmetic part of the ALU.

The ATtiny28 contains 2K bytes of on-chip Flash memory for program storage. Since all instructions are single 16-bit words, the Flash is organized as 1K x 16 words. The Flash memory has an endurance of at least 1,000 write/erase cycles.

The ATtiny28 program counter is 10 bits wide, thus addressing the 1K word Flash program memory. See page 44 for a detailed description of Flash data downloading.

The ATtiny28 AVR RISC microcontroller supports powerful and efficient addressing modes. This section describes the different addressing modes supported in the ATtiny28. 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.

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Figure 7. Direct Single Register Addressing

The operand is contained in register d (Rd).

Register Indirect Figure 8. Indirect Register Addressing

Register Direct, Two Registers Rd and Rr

REGISTERFILE

Z-Register

30 31

The register accessed is the one pointed to by the Z-register (R31, R30).

Figure 9. Direct Register Addressing, Two Registers

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

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I/O Direct Figure 10. 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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Relative Program Addressing, RJMP and RCALL

Constant Addressing Using the LPM Instruction

Figure 11. Relative Program Memory Addressing

15 0

15 012 11

PROGRAM MEMORY

$000

$3FF

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

2047.

Figure 12. Code Memory Constant Addressing

PROGRAM MEMORY

15 1 0

Z-REGISTER

$000

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$3FF

Constant byte address is specified by the Z-register contents. The 15 MSBs select word address (0 - 1K), and LSB selects low byte if cleared (LSB = 0) or high byte if set (LSB =

1).

Subroutine and Interrupt Hardware Stack

The ATtiny28 uses a 3-level-deep hardware stack for subroutines and interrupts. The hardware stack is 10 bits wide and stores the program counter (PC) return address while subroutines and interrupts are executed.

RCALL instructions and interrupts push the PC return address onto stack level 0, and the data in the other stack levels 1 - 2 are pushed one level deeper in the stack. When a RET or RETI instruction is executed the returning PC is fetched from stack level 0, and the data in the other stack levels 1 - 2 are popped one level in the stack.

If more than three subsequent subroutine calls or interrupts are executed, the first values written to the stack are overwritten.

Memory Access 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, directly generated from the external clock crystal for the chip. No internal clock division is used.

Figure 13 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.

Figure 13. 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 14 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 14. Single Cycle ALU Operation

T1 T2 T3 T4

System Clock Ø

Total Execution Time

ALU Operation Execute

Result Write Back

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I/O Memory The I/O space definition of the ATtiny28 is shown in Table 2.

Table 2. ATtiny28 I/O Space

Address Hex Name Function

$3F SREG Status Register

$1B PORTA Data Register, Port A

$1A PACR Port A Control Register

$19 PINA Input Pins, Port A

$16 PINB Input Pins, Port B

$12 PORTD Data Register, Port D

$11 DDRD Data Direction Register, Port D

$10 PIND Input Pins, Port D

$08 ACSR Analog Comparator Control and Status Register

$07 MCUCS MCU Control and Status Register

$06 ICR Interrupt Control Register

$05 IFR Interrupt Flag Register

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$04 TCCR0 Timer/Counter0 Control Register

$03 TCNT0 Timer/Counter0 (8-bit)

$02 MODCR Modulation Control Register

$01 WDTCR Watchdog Timer Control Register

$00 OSCCAL Oscillator Calibration Register

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

All ATtiny28 I/O 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.

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

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

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

Bit 76543210

$3F 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

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• 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

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 arithmetic. 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

⊕ V

Reset and Interrupt Handling

The zero flag Z indicates a zero result from an arithmetical or logical 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.

The ATtiny28 provides five different interrupt sources. These interrupts and the reset vector each have a separate program vector in the program memory space. All the interrupts are assigned to individual enable bits. In order to enable the interrupt, both the individual enable bit and the I-bit in the status register (SREG) must be set to one.

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 3. 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.

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Table 3. Reset and Interrupt Vectors

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Vector

No.

1 $000 RESET

2 $001 INT0 External Interrupt Request 0

3 $002 INT1 External Interrupt Request 1

4 $003 Input Pins Low-level Input on Port B

5 $004

6 $005 ANA_COMP Analog Comparator

Program Address Source Interrupt Definition

Hardware Pin, Power-on Reset and Watchdog Reset

TIMER0, OVF0

Timer/Counter0 Overflow

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 LOW_LEVEL ; Low level input handler

$004 rjmp TIM0_OVF ; Timer0 overflow handle

$005 rjmp ANA_COMP ; Analog Comparator handle

;

$006 MAIN: <instr> xxx ; Main program start

…… ……

Reset Sources The ATtiny28 provides 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 then 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 placed at these locations. The circuit diagram in Figure 15 shows the reset logic. Table 4 defines the timing and electrical parameters of the reset circuitry.

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Figure 15. Reset Logic

DATA BUS

MCU Control and Status

PORF

WDRF

EXTRF

VCC

100 - 500K

RESET

Power-on

Reset Circuit

SRQ

Watchdog

Timer

CKSEL[3..0]

COUNTER RESET

On-chip

RC Oscillator

Delay Counters

Full

Table 4. Reset Characteristics

Symbol Parameter Min Typ Max Unit

(1)

POT

RST

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

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

RESET Pin Threshold Voltage 0.6 V

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

(falling).

INTERNAL RESET

POT

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Table 5. ATtiny28 Clock Options and Start-up Time

CKSEL3..0 Clock Source Start-up Time at 2.7V

1111 External Crystal/Ceramic Resonator

1110 External Crystal/Ceramic Resonator

1101 External Crystal/Ceramic Resonator

1100 External Crystal/Ceramic Resonator 16K CK

1011 External Crystal/Ceramic Resonator 4.2 ms + 16K CK

1010 External Crystal/Ceramic Resonator 67 ms + 16K CK

1001 External Low-frequency Crystal 67 ms + 1K CK

1000 External Low-frequency Crystal 67 ms + 32K CK

0111 External RC Oscillator 6 CK

0110 External RC Oscillator 4.2 ms + 6 CK

0101 External RC Oscillator 67 ms + 6 CK

(1)

1K CK

4.2 ms + 1K CK

67 ms + 1K CK

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Table 5. ATtiny28 Clock Options and Start-up Time (Continued)

CKSEL3..0 Clock Source Start-up Time at 2.7V

0100 Internal RC Oscillator 6 CK

0011 Internal RC Oscillator 4.2 ms + 6 CK

0010 Internal RC Oscillator 67 ms + 6 CK

0001 External Clock 6 CK

0000 External Clock 4.2 ms + 6 CK

Note: 1. Due to limited number of clock cycles in the start-up period, it is recommended that

ceramic resonator be used.

This table shows the start-up times from reset. From Power-down mode, only the clock counting part of the start-up time is used. The Watchdog oscillator is used for timing the real-time part of the start-up time. The number WDT oscillator cycles used for each time-out is shown in Table 6.

Table 6. Number of Watchdog Oscillator Cycles

Time-out Number of Cycles

4.2 ms 1K

67 ms 16K

The frequency of the Watchdog oscillator is voltage-dependent, as shown in the section “Typical Characteristics” on page 55.

The device is shipped with CKSEL = 0010.

Power-on Reset A Power-on Reset (POR) pulse is generated by an on-chip detection circuit. The detec-

tion level is nominally 1.4V. The POR is activated whenever V

is below the detection

level. The POR circuit can be used to trigger the start-up reset, as well as detect a failure in supply voltage.

The Power-on Reset (POR) circuit ensures that the device is reset from power-on. Reaching the Power-on Reset threshold voltage invokes a delay counter, which determines the delay for which the device is kept in RESET after V

rise. The time-out

period of the delay counter can be defined by the user through the CKSEL fuses. The different selections for the delay period are presented in Table 5. The RESET signal is activated again, without any delay, when the V

decreases below detection level. See

Figure 16.

If the built-in start-up delay is sufficient, RESET an external pull-up resistor. By holding the RESET

can be connected to VCC directly or via

pin low for a period after VCC has been applied, the Power-on Reset period can be extended. Refer to Figure 17 for a timing example of this.

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Figure 16. MCU Start-up, RESET Tied to VCC.

VCC

RESET

TIME-OUT

INTERNAL

RESET

POT

RST

TOUT

Figure 17. 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 voltage 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 18. External Reset during Operation

VCC

RESET

RST

pin. Reset pulses longer

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TIME-OUT

INTERNAL

RESET

TOUT

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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 26 for details on operation of the Watchdog.

TOUT

Figure 19. Watchdog Reset during Operation

MCU Control and Status Register – MCUCS

The MCU Control and Status Register contains control and status bits for general MCU functions.

Bit 76543210

$07 PLUPB – SE SM WDRF – EXTRF PORF MCUCS

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

Initial Value 0 0 0 0 See Bit

Desc.

0 See Bit Description

• Bit 7 – PLUPB: Pull-up Enable Port B

When the PLUPB bit is set (one), pull-up resistors are enabled on all Port B input pins. When PLUPB is cleared, the pull-ups are disabled. If any of the special functions of Port B is enabled, the corresponding pull-up(s) is disabled, independent of the value of PLUPB.

• Bit 6 – Res: Reserved Bit

This bit is a reserved bit in the ATtiny28 and always reads as zero.

• Bit 5 – 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.

• Bit 4 – SM: Sleep Mode

This bit selects between the two available sleep modes. When SM is cleared (zero), Idle Mode is selected as sleep mode. When SM is set (one), Power-down mode is selected as sleep mode. For details, refer to “Sleep Modes” below.

• Bit 3 – WDRF: Watchdog Reset Flag

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This bit is set if a Watchdog reset occurs. The bit is cleared by a Power-on Reset, or by writing a logical “0” to the flag.

• Bit 2 – Res: Reserved Bit

This bit is a reserved bit in the ATtiny28 and always reads as zero.

• Bit 1 – EXTRF: External Reset Flag

This bit is set if an external reset occurs. The bit is cleared by a Power-on Reset, or by writing a logical “0” to the flag.

• Bit 0 – PORF: Power-on Reset Flag

This bit is set if a Power-on Reset occurs. The bit is cleared by writing a logical “0” to the flag.

To make use of the reset flags to identify a reset condition, the user should read and then clear the flag bits in MCUCS as early as possible in the program. If the register is cleared before another reset occurs, the source of the reset can be found by examining the reset flags.

Interrupt Handling The ATtiny28 has one 8-bit Interrupt Control Register (ICR).

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.

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.

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

minimum. After four clock cycles the program vector address for the actual interrupt handling routine is executed. During this 4-clock-cycle period, the program counter (10 bits) is pushed onto the stack. 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. If an interrupt occurs when the MCU is in sleep mode, the interrupt execution response time is increased by four clock cycles.

A return from an interrupt handling routine takes four clock cycles. During these four clock cycles, the program counter (10 bits) is popped back from the stack, and the I-flag in SREG is set. When AVR exits from an interrupt, it will always return to the main program and execute one more instruction before any pending interrupt is served.

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Interrupt Control Register – ICR

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Bit 76543210

$06 INT1 INT0 LLIE TOIE0 ISC11 ISC10 ISC01 ISC00 ICR

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 – INT1: External Interrupt Request 1 Enable

When the INT1 bit is set (one) and I-bit in the Status Register (SREG) is set (one), the external pin interrupt 1 is enabled. The interrupt Sense Control1 bits 1/0 (ISC11 and ISC10) define whether the external interrupt is activated on rising or falling edge, on pin change or low level of the INT1 pin. The corresponding interrupt of External Interrupt Request 1 is executed from program memory address $002. See also “External Interrupt”.

• 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 0 is enabled. The interrupt Sense Control0 bits 1/0 (ISC01 and ISC00) define whether the external interrupt is activated on rising or falling edge, on pin change or low level of the INT0 pin. The corresponding interrupt of External Interrupt Request 0 is executed from program memory address $001. See also “External Interrupt”.

• Bit 5 – LLIE: Low-level Input Interrupt Enable

When the LLIE is set (one) and the I-bit in the status register (SREG) is set (one), the interrupt on low-level input is activated. Any of the Port B pins pulled low will then cause an interrupt. However, if any Port B pins are used for other special features, these pins will not trigger the interrupt. The corresponding interrupt of Low-level Input Interrupt Request is executed from program memory address $003. See also “Low-level Input Interrupt”.

• Bit 4 – 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 $004) is executed if an overflow in Timer/Counter0 occurs, i.e., when the TOV0 bit is set in the Interrupt Flag Register (IFR).

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

The External Interrupt 1 is activated by the external pin INT1 if the SREG I-flag and the corresponding interrupt enable are set. The level and edges on the external INT1 pin that activate the interrupt are defined in Table 7.

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Table 7. Interrupt 1 Sense Control

ISC11 ISC10 Description

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

0 1 Any change on INT1 generates an interrupt request.

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

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

Note: When changing the ISC11/ISC10 bits, INT1 must be disabled by clearing its Interrupt

Enable bit. Otherwise, an interrupt can occur when the bits are changed.

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

The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corresponding interrupt enable are set. The level and edges on the external INT0 pin that activate the interrupt are defined in Table 8.

Table 8. Interrupt 0 Sense Control

ISC01 ISC00 Description

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

0 1 Any change on INT0 generates an interrupt request.

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

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

Note: When changing the ISC01/ISC00 bits, INT0 must be disabled by clearing its Interrupt

Enable bit. Otherwise, an interrupt can occur when the bits are changed.

Interrupt Flag Register – IFR

The value on the INT pins are 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 76543210

$05 INTF1 INTF0 – TOV0 ––––IFR

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

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – INTF1: External Interrupt Flag1

When an edge on the INT1 pin triggers an interrupt request, the corresponding interrupt flag, INTF1 becomes set (one). If the I-bit in SREG and the corresponding interrupt enable bit, INT1 in GIMSK is set (one), the MCU will jump to the interrupt vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical “1” to it. This flag is always cleared when INT1 is configured as level interrupt.

• Bit 6 – INTF0: External Interrupt Flag0

When an edge on the INT0 pin triggers an interrupt request, the corresponding interrupt flag, INTF0 becomes set (one). If the I-bit in SREG and the corresponding interrupt enable bit, INT0 in GIMSK is set (one), the MCU will jump to the interrupt vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be

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cleared by writing a logical “1” to it. This flag is always cleared when INT0 is configured as level interrupt.

• Bit 5 – Res: Reserved Bit

This bit is a reserved bit in the ATtiny28 and always reads as zero.

• Bit 4 – 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. TOV0 is cleared by writing a logical “1” to the flag. When the SREG I-bit, TOIE0 in ICR and TOV0 are set (one), the Timer/Counter0 Overflow interrupt is executed.

• Bit 3..0 - Res: Reserved Bits

These bits are reserved bits in the ATtiny28 and always read as zero.

Note: 1. One should not try to use the SBI (Set Bit in I/O Register) instruction to clear individ-

ual flags in the Register. This will result in clearing all the flags in the register, because the register is first read, then modified and finally written, thus writing ones to all set flags. Using the CBI (Clear Bit in I/O Register) instruction on IFR will result in clearing all bits apart from the specified bit.

External Interrupt The external interrupt is triggered by the INT pins. Observe that, if enabled, the interrupt

will trigger even if the INT pin is configured as an output. This feature provides a way of generating a software interrupt. The external interrupt can be triggered by a falling or rising edge, a pin change or a low level. This is set up as indicated in the specification for the Interrupt Control Register (ICR). 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 interrupt is set up as described in the specification for the Interrupt Control Register (ICR).

Low-level Input Interrupt The low-level interrupt is triggered by setting any of the Port B pins low. However, if any

Port B pins are used for other special features, these pins will not trigger the interrupt. For example, if the analog comparator is enabled, a low level on PB0 or PB1 will not cause an interrupt. This is also the case for the special functions T0, INT0 and INT1. If low-level interrupt is selected, the low level must be held until the completion of the currently executing instruction to generate an interrupt. When this interrupt is enabled, the interrupt will trigger as long as any of the Port B pins are held low.

Sleep Modes To enter the sleep modes, the SE bit in MCUCS must be set (one) and a SLEEP instruc-

tion must be executed. The SM bit in the MCUCS register selects which sleep mode (Idle or Power-down) will be activated by the SLEEP instruction. If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU awakes. The CPU is then halted for four cycles. It executes the interrupt routine and resumes execution from the instruction following SLEEP. The contents of the register file 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 SM bit is cleared (zero), the SLEEP instruction forces the MCU into the Idle

Mode, stopping the CPU but allowing 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 Timer Overflow interrupt and Watchdog reset. If wake-up from the Analog 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. Note that the ACD bit is set by default.

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Power-down Mode When the SM bit is set (one), the SLEEP instruction forces the MCU into 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 if a level-triggered interrupt is used for wake-up from Power-down mode, the changed level must be held for some time to wake up the MCU. This makes the MCU less sensitive to noise. The wake-up period is equal to the clock-counting part of the reset period (see Table 5). The MCU will wake up from power-down if the input has the required level for two Watchdog oscillator cycles. If the wake-up period is shorter than two Watchdog oscillator cycles, the MCU will wake up if the input has the required level for the duration of the wake-up period. If the wake-up condition disappears before the wake-up period has expired, the MCU will wake up from power-down without executing the corresponding interrupt. The period of the Watchdog oscillator is 2.7 µs (nominal) at

3.0V and 25 shown in the section “Typical Characteristics” on page 55.

When waking up from the Power-down mode, there is a delay from the wake-up condition until the wake-up becomes effective. This allows the clock to restart and become stable after having been stopped.

°C. The frequency of the watchdog oscillator is voltage-dependent as

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Timer/Counter0 The ATtiny28 provides one general-purpose 8-bit Timer/Counter – Timer/Counter0.

Timer/Counter0 has prescaling selection from the 10-bit prescaling timer. The Timer/Counter0 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 Prescaler Figure 20 shows the Timer/Counter prescaler.

Figure 20. Timer/Counter0 Prescaler

COUNT ENABLE

FROM MODULATOR

CS00 CS01 CS02

10-BIT T/C PRESCALER

CK/64

TIMER/COUNTER0 CLOCK SOURCE

TCK0

CK/256

CK/1024

The four different prescaled selections are: the hardware modulator period, CK/64, CK/256 and CK/1028, where CK is the oscillator clock. CK, external source and stop can also be selected as clock sources.

Figure 21 shows the block diagram for Timer/Counter0.

Figure 21. Timer/Counter0 Block Diagram

T/C0 OVER-

FLOW IRQ

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INTERRUPT CONTROL

TOIE0

TIMER/COUNTER0

(TCNT0)

TOV0

INTERRUPT FLAG

TOV0

T/C0 CONTROL

CONTROL

LOGIC

Timer/Counter0 Control Register – TCCR0

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 Interrupt Flag Register (IFR). Control signals are found in the Timer/Counter0 Control Register (TCCR0). The interrupt enable/disable setting for Timer/Counter0 is found in the Interrupt Control Register (ICR).

When Timer/Counter0 is externally clocked, the external signal is synchronized with the oscillator frequency of the CPU. To ensure 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 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.

Bit 7 6 5 4 3 210

$04 FOV0 ––OOM01 OOM00 CS02 CS01 CS00 TCCR0

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

Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – FOV0: Force Overflow

Writing a logical “1” to this bit forces a change on the overflow output pin PA2 according to the values already set in OOM01 and OOM00. If the OOM01 and OOM00 bits are written in the same cycle as FOV0, the new settings will not take effect until the next overflow or forced overflow occurs. The Force Overflow bit can be used to change the output pin without waiting for an overflow in the timer. The automatic action programmed in OOM01 and OOM00 happens as if an overflow had occurred, but no interrupt is generated. The FOV0 bit will always read as zero, and writing a zero to this bit has no effect.

• Bits 6, 5 – Res: Reserved Bits

These bits are reserved bits in the ATtiny28 and always read as zero.

• Bits 4, 3 – OOM01, OOM00: Overflow Output Mode, Bits 1 and 0

The OOM01 and OOM00 control bits determine any output pin action following an overflow or a forced overflow in Timer/Counter0. Any output pin actions affect pin PA2. The control configuration is shown in Table 9.

Table 9. Overflow Output Mode Select

OOM01 OOM00 Description

0 0 Timer/Counter0 disconnected from output pin PA2

0 1 Toggle the PA2 output line.

1 0 Clear the PA2 output line to zero.

1 1 Set the PA2 output line to one.

• 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.

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Timer Counter 0 – TCNT0

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Table 10. Clock 0 Prescale Select

CS02 CS01 CS00 Description

0 0 0 Stop, the Timer/Counter0 is stopped.

001CK

0 1 0 Modulator Period

011CK/64

100CK/256

1 0 1 CK/1024

1 1 0 External Pin T0, falling edge

1 1 1 External Pin T0, 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 for Timer/Counter0, transitions on PB2/(T0) will clock the counter even if the pin is configured as an output. This feature can give the user software control of the counting.

Bit 76543210

$03 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 timer clock cycle following the write operation.

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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 11. 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 ATtiny28 resets and executes from the reset vector. For timing details on the Watchdog reset, refer to page 17.

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 22. Watchdog Timer

Oscillator

1 MHz at V

350 kHz at V

110 kHz at V

= 5V

= 3V

= 2V

levels. The WDR

Watchdog Timer Control Register – WDTCR

Bit 765 4 3210

$01 –––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

• Bits 7..5 - Res: Reserved Bits

These bits are reserved bits in the ATtiny28 and will always read as zero.

• 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 one before the disable operation starts.

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

Watchdog.

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• 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 11.

Table 11. Watchdog Timer Prescale Select

Number of WDT Oscillator

WDP2 WDP1 WDP0

0 0 0 16K cycles 0.15 s 47 ms 15 ms

0 0 1 32K cycles 0.30 s 94 ms 30 ms

0 1 0 64K cycles 0.60 s 0.19 s 60 ms

0 1 1 128K cycles 1.2 s 0.38 s 0.12 s

1 0 0 256K cycles 2.4 s 0.75 s 0.24 s

1 0 1 512K cycles 4.8 s 1.5 s 0.49 s

1 1 0 1,024K cycles 9.6 s 3.0 s 0.97 s

1 1 1 2,048K cycles 19 s 6.0 s 1.9 s

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

“Typical Characteristics” on page 55. 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 counting from zero.

Cycles

Typical Time-out at

= 2.0V

Typ i cal Time-out at

= 3.0V

Typ i cal Time-out at

= 5.0V

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Calibrated Internal RC Oscillator

Oscillator Calibration Register – OSCCAL

The calibrated internal oscillator provides a fixed 1.2 MHz (nominal) clock at 3V and

°C. This clock may be used as the system clock. See the section “Clock Options” on

25 page 4 for information on how to select this clock as the system clock. This oscillator can be calibrated by writing the calibration byte to the OSCCAL register. When this oscillator is used as the chip clock, the Watchdog oscillator will still be used for the Watchdog Timer and for the reset time-out. For details on how to use the pre-programmed calibration value, see the section “Calibration Byte” on page 44.

Bit 76543210

$00 CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL

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 – CAL7..CAL0: Oscillator Calibration Value

Writing the calibration byte to this address will trim the internal oscillator to remove process variation from the oscillator frequency. When OSCCAL is zero, the lowest available frequency is chosen. Writing non-zero values to the register will increase the frequency to the internal oscillator. Writing $FF to the register gives the highest available frequency. Table 12 shows the range for OSCCAL. Note that the oscillator is intended for calibration to 1.2 MHz, thus tuning to other values is not guaranteed. At 3V and 25

C, the pre-programmed calibration byte gives a frequency within ± 1% of the nominal frequency.

Table 12. Internal RC Oscillator Range

OSCCAL Value Min Frequency Max Frequency

0x00 0.6 MHz 1.2 MHz

0x7F 0.8 MHz 1.7 MHz

0xFF 1.2 MHz 2.5 MHz

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Hardware Modulator ATtiny28 features a built-in hardware modulator connected to a high-current output pad,

PA2. The hardware modulator generates a configurable pulse train. The on-time of a pulse can be set to a number of chip clock cycles. This is done by configuring the Modulation Control Register (MODCR).

Modulation Control Register – MODCR

Bit 76543 2 1 0

$02

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

ONTIM4 ONTIM3 ONTIM2 ONTIM1 ONTIM0 MCONF2 MCONF1 MCONF0 MODCR

• Bits 7..3 – ONTIM4..0: Modulation On-time

This 5-bit value +1 determines the number of clock cycles the output pin PA2 is active (low).

• Bits 2..0 – MCONF2..0: Modulation Configuration Bits 2, 1 and 0

These three bits determine the relationship between the on- and off-times of the modulator, and thereby the duty-cycle. The various settings are shown in Table 13. The minimum and maximum modulation period is also shown in the table. The minimum modulation period is obtained by setting ONTIM to zero, while the maximum period is obtained by setting ONTIM to 31. The configuration values for some common oscillator and carrier frequencies are listed in Table 15. The relationship between oscillator frequency and carrier frequency is:

fcarrier

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

()

On-time Off-time+

fosc

If the MCONF register is set to 111, the carrier frequency will be equal to the oscillator frequency.

Table 13. MCONF2..0 Effect on Duty-cycle and Modulation Period

MCONF2..0 On-time Off-time Duty-cycle Min Period Max Period Comment

000 X X 100% X X Unmodulated output

001 ONTIM+1 ONTIM+1 50% 2 CK 64 CK

010 ONTIM+1 2 x (ONTIM+1) 33% 3 CK 96 CK

011 ONTIM+1 3 x (ONTIM+1) 25% 4 CK 128 CK

100 2 x (ONTIM+1) ONTIM+1 67% 3 CK 96 CK

101 3 x (ONTIM+1) ONTIM+1 75% 4 CK 128 CK

110 Reserved

111 X X Note 1 1 CK 1 CK High-frequency output

Note: In the high-frequency mode, the output is gated with the clock signal. Thus, the on- and off-times will be dependent on the clock

input to the MCU. Also note that when changing from this mode directly to another modulation mode, the output will have a small glitch. Thus, PA2 should be set to stop the modulated output before changing from this mode.

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PA2 is the built-in, high-current LED driver and it is always an output pin. The output buffer can sink 25 mA at V

= 2.0V. When MCONF is zero, modulation is switched off

and the pin acts as a normal high-current output pin. The following truth table shows the effect of various PORTA2 and MCONF settings.

Table 14. PA2 Output

PORTA2 MCONF PA2 Output

000

0 1 - 7 Modulated

1X1

The modulation period is available as a prescale to Timer/Counter0 and thus, this timer should be used to time the length of each burst. If the number of pulses to be sent is N, the number 255 - N should be loaded to the timer. When an overflow occurs, the transmission is complete.The OOM01 and OOM00 bits in TCCR0 can be configured to automatically change the value on PA2 when a Timer/Counter0 overflow occurs. See “Timer/Counter0” on page 23 for details on how to configure the OOM01 and OOM00 bits.

The modulation period is available as a prescale even when PORTA2 is high and modulation is stopped. Thus, this prescale can also be used to time the intervals between bursts.

To get a glitch-free output, the user should first configure the MODCR register to enable modulation. There are two ways to start the modulation:

1. Clear the PORTA2 bit in Port A Data Register (PORTA).

2. Configure OOM00 and OOM01 bits in the Timer/Counter0 Control Register

(TCCR0) to clear PA2 on the next overflow. Either an overflow or a forced overflow can then be used to start modulation.

The PA2 output will then be set low at the start of the next cycle. To stop the modulated output, the user should set the PORTA2 bit or configure OOM00 and OOM01 to set PA2 on the next overflow. If the MODCR register is changed during modulation, the changed value will take effect at the start of the next cycle, producing a glitch-free output. See Figure 23 below and Figure 30 on page 38.

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Figure 23. The Hardware Modulator

RM 8

ONTIM

MCONF

FROM

PORTA2

IONTIM

IMCONF

IPORTA2

ATtiny28L/V

MODULATOR

STATE

MACHINE

DISABLE MODUALTOR

ENABLE SETTING

COUNT ENABLE TO TIMER/COUNTER0

WM: WRITE MODCR RM: READ MODCR

PA2

0 1

Figure 24 to Figure 27 show examples on output from the Modulator. Figure 24 also shows the timing for the enable setting signal and for the count enable signal to Timer/Counter0.

Figure 24. Modulation with ONTIM = 3, MCONF = 010.

CLK

PA 2

ENABLE

SETTING

COUNT

ENABLE

Note: 1. Clock frequency: 455 kHz; modulation frequency: 38 kHz; duty-cycle: 33%

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Figure 25. Modulation with ONTIM = 5, MCONF = 001

CLK

PA 2

Note: Clock frequency: 455 kHz; modulation frequency: 38 kHz; duty-cycle: 50%

Figure 26. Modulation with ONTIM = 1, MCONF = 011

CLK

PA 2

Note: Clock frequency: 3.64 MHz; modulation frequency: 455 kHz; duty-cycle: 25%

Figure 27. Modulation with ONTIM = 3, MCONF = 001

CLK

PA 2

Note: Clock frequency: 3.64 MHz; modulation frequency: 455 kHz; duty-cycle: 50%

Table 15. Some Common Modulator Configurations

Crystal/Resonator Frequency

455 kHz 38 kHz 0.2 25% 2 011

455 kHz 38 kHz 0.2 33% 3 010

455 kHz 38 kHz 0.2 50% 5 001

455 kHz 38 kHz 0.2 67% 3 100

455 kHz 38 kHz 0.2 75% 2 101

1 MHz 38 kHz 1.2 50% 12 001

1.8432 MHz 38 kHz 1.1 25% 11 011

1.8432 MHz 38 kHz 1.1 33% 15 010

1.8432 MHz 38 kHz 1.1 50% 23 001

2 MHz 38 kHz 1.2 25% 12 011

2 MHz 38 kHz 1.2 50% 25 001

2.4576 MHz 38 kHz 1.1 50% 31 001

3.2768 MHz 38 kHz 2.0 25% 21 011

4 MHz 38 kHz 1.2 25% 25 011

455 kHz 455 kHz 0.0 approx. 50% X 111

1 MHz 455 kHz 9.9 50% 0 001

Carrier Frequency

% Error in Frequency Duty-cycle

ONTIM Value

MCONF Value

1.82 MHz 455 kHz 0.0 25% 0 011

1.82 MHz 455 kHz 0.0 50% 1 001

1.8432 MHz 455 kHz 1.3 25% 0 011

1.8432 MHz 455 kHz 1.3 50% 1 001

2 MHz 455 kHz 9.9 25% 0 011

2 MHz 455 kHz 9.9 50% 1 001

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Table 15. Some Common Modulator Configurations (Continued)

ATtiny28L/V

Crystal/Resonator Frequency

2.4576 MHz 455 kHz 10.0 33% 1 010

2.4576 MHz 455 kHz 10.0 50% 2 001

3.2768 MHz 455 kHz 10.0 25% 1 011

3.2768 MHz 455 kHz 10.0 50% 3 001

3.64 MHz 455 kHz 0.0 25% 1 011

3.64 MHz 455 kHz 0.0 50% 3 001

4 MHz 455 kHz 9.9 25% 1 011

4 MHz 455 kHz 9.9 50% 3 001

Carrier Frequency

% Error in Frequency Duty-cycle

ONTIM Value

MCONF Value

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Analog Comparator The analog comparator compares the input values on the positive input PB0 (AIN0) and

negative input PB1 (AIN1). When the voltage on the positive input PB0 (AIN0) is higher than the voltage on the negative input PB1 (AIN1), the Analog Comparator Output (ACO) is set (one). 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

Figure 28. Analog Comparator Block Diagram

PB0

PB1

Analog Comparator Control and Status Register – ACSR

Bit 76543210

$08 ACD – ACO ACI AC IE – ACIS1 ACIS0 ACSR

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

Initial Value 1 0 X 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. To use the analog comparator, the user must clear this bit.

• Bit 6 – Res: Reserved Bit

This bit is a reserved bit in the ATtiny28 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.

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• Bit 2 – RES: Reserved Bit

This bit is a reserved bit in the ATtiny28 and will always read as zero.

• 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 16.

Table 16. 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 one back into ACI if it is read as set, thus clearing the flag.

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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 a 4-bit I/O port. PA2 is output-only, while PA3, PA1 and PA0 are bi-directional.

Three I/O memory address locations are allocated for Port A, one each for the Data Register – PORTA, $1B, Port A Control Register – PACR, $1A and the Port A Input Pins – PINA, $19. The Port A Input Pins address is read-only, while the Data Register and the Control Register are read/write. Compared to other output ports, the Port A output is delayed one extra clock cycle.

Port pins PA0, PA1 and PA3 have individually selectable pull-up resistors. When pins PA0, PA1 or PA3 are used as inputs and are externally pulled low, they will source current if the internal pull-up resistors are activated. PA2 is output-only. The PA2 output buffer can sink 25 mA and thus drive a high-current LED directly. This output can also be modulated (see “Hardware Modulator” on page 29 for details).

Port A Data Register – PORTA

Bit 76543210

$1B

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

Initial Value 0 0 0 0 0 1 0 0

––––PORTA3 PORTA2 PORTA1 PORTA0 PORTA

Port A Control Register – PAC R

Bit 76543210

$1A ––––DDA3 PA2HC DDA1 DDA0 PACR

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

Initial Value 0 0 0 0 0 0 0 0

• Bits 7..4 – Res: Reserved Bits

These bits are reserved bits in the ATtiny28 and always read as zero.

• Bit 3 – DDA3: Data Direction PA3

When DDA3 is set (one), the corresponding pin is an output pin. Otherwise, it is an input pin.

• Bit 2 – PA2HC: PORTA2 High Current Enable

When the PA2HC bit is set (one), an additional driver at the output pin PA2 is enabled. This makes it possible to sink 25 mA at V cleared (zero), PA2 can sink 15 mA at V

= 1.8V (VOL = 0.8V). When the PA2HC bit is

= 1.8V (VOL = 0.8V).

• Bits 1, 0 – DDA1, DDA0: Data Direction PA1 and PA0

When DDAn is set (one), the corresponding pin is an output pin. Otherwise, it is an input pin.

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Port A as General Digital I/O PA3, PA1 and PA0 are general I/O pins. The DDAn (n: 3,1,0) bits in PACR select the

direction of these pins. 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 bit has to be cleared (zero) or the pin has to be configured as an output pin. The effects of the DDAn and PORTAn bits on PA3, PA1 and PA0 are shown in Table 17. The port pins are tri-stated when a reset condition becomes active, even if the clock is not running.

Table 17. 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: 3,1,0, pin number

Port A Input Pins Address – PINA

Bit 76543210

$19 ––––PINA3 – PINA1 PINA0 PINA

Read/WriteRRRRRRRR

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

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.

Alternate Function of PA2 PA2 is the built-in, high-current LED driver and it is always an output pin. The output sig-

nal can be modulated with a software programmable frequency. See “Hardware Modulator” on page 29 for further details.

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

shown in the figures.

Figure 29. Port A Schematic Diagram (Pins PA0, PA1 and PA3)

MOS

PULL-

RESET

DDAn

RESET

PORTAn

DATA BUS

PAn

RESET

WRITE PORTA

WP:

WRITE DDRA

WD:

READ PORTA LATCH

RL:

READ PORTA PIN

RP:

READ DDRA

RD:

0,1,3

Figure 30. Port A Schematic Diagram (Pin PA2)

PA2

WP:

WRITE PORTA

RL:

READ PORTA LATCH

Note: Both the flip-flops shown have reset value one (set).

HARDWARE

MODULATOR

RESET

OOM01

0 0 1 1

DATA BUS

OOM00

0 1 0 1

PORTA2

DISABLE

TOGGLE

CLEAR

SET

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TOV0 FOV0

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Port B Port B is an 8-bit input port.

One I/O address location is allocated for the Port B Input Pins – PINB, $16. The Port B Input Pins address is read-only.

All port pins have pull-ups that can be switched on for all Port B pins simultaneously. If any of the Port B special functions is enabled, the corresponding pull-up(s) is disabled. When pins PB0 to PB7 are externally pulled low, they will source current (I nal pull-up resistors are activated.

The Port B pins with alternate functions are shown in Table 18.

Table 18. Port B Pin Alternate Functions

Port Pin Alternate Functions

PB0 AIN0 (Analog Comparator Positive Input)

PB1 AIN1 (Analog Comparator Negative Input)

PB2 T0 (Timer/Counter 0 External Counter Input)

PB3 INT0 (External Interrupt 0 Input)

PB4 INT1 (External Interrupt 1 Input)

ATtiny28L/V

) if the inter-

Port B Input Pins Address – PINB

Bit 76543210

$16 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

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

Port B as General Digital Input All eight pins in Port B have equal functionality when used as digital input pins.

PBn, general input pin: To switch the pull-up resistors on, the PLUPB bit in the MCUCS register must be set (one). This bit controls the pull-up on all Port B pins. To turn the pull-ups off, this bit has to be cleared (zero). Note that if any Port B pins are used for alternate functions, the pull-up on the corresponding pins are disabled. The port pins are tri-stated when a reset condition becomes active, even if the clock is not running.

Alternate Functions of Port B All Port B pins are connected to a low-level detector that can trigger the low-level input

interrupt. See “Low-level Input Interrupt” on page 21 for details. In addition, Port B has the following alternate functions:

• INT1 – Port B, Bit 4

INT1, External Interrupt source 1. The PB4 pin can serve as an external interrupt source to the MCU. See the interrupt description for details on how to enable and configure this interrupt. If the interrupt is enabled, the pull-up resistor on PB4 is disabled and PB4 will not give low-level interrupts.

• INT0 – Port B, Bit 3

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INT0, External Interrupt source 0. The PB3 pin can serve as an external interrupt source to the MCU. See the interrupt description for details on how to enable and configure this interrupt. If the interrupt is enabled, the pull-up resistor on PB3 is disabled and PB3 will not give low-level interrupts.

• T0 – Port B, Bit 2

T0, Timer/Counter0 Counter source. See the timer description for further details. If T0 is used as the counter source, the pull-up resistor on PB2 is disabled and PB2 will not give low-level interrupts.

• AIN1 – Port B, Bit 1

AIN1, Analog Comparator Negative input. When the on-chip analog comparator is enabled, this pin also serves as the negative input of the comparator. If the analog comparator is enabled, the pull-up resistors on PB1 and PB0 are disabled and these pins will not give low-level interrupts.

• AIN0 – Port B, Bit 0

AIN0, Analog Comparator Positive input. When the on-chip analog comparator is enabled, this pin also serves as the positive input of the comparator. If the analog comparator is enabled, the pull-up resistors on PB1 and PB0 are disabled and these pins will not give low-level interrupts.

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

shown in the figures.

Figure 31. Port B Schematic Diagram (Pins PB0 and PB1)

MOS PULLUP

PBn

RP: READ PORTB PIN n : 0, 1

PWRDN

PULL-UP PORT B

COMPARATOR DISABLE

TO LOW-LEVEL DETECTOR

TO COMPARATOR

AINn

TA BUS DA

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Figure 32. Port B Schematic Diagram (Pin PB2)

ATtiny28L/V

MOS PULLUP

PB2

RP: READ PORTB PIN

SENSE CONTROL

CS02 CS01 CS00

PULL-UP PORT B

TO LOW-LEVEL DETECTOR

Figure 33. PORT B Schematic Diagram (Pins PB3 and PB4)

DATA BUS

TIMER0 CLOCK SOURCE MUX

MOS PULLUP

PBn

RP: READ PORTB PIN n : 3, 4 m : 0, 1

SENSE CONTROL

ISCm1 ISCm0

PULL-UP PORT B

INTm ENABLE

DATA BUS

TO LOW-LEVEL DETECTOR

INTm

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Figure 34. PORT B Schematic Diagram (Pins PB7 - PB5)

PBn

MOS PULLUP

RP:n:READ PORT B PIN

5 - 7

PULL-UP PORT B

TO LOW-LEVEL DETECTOR

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, Data Direction Register – DDRD, $11 and the Port D Input Pins – PIND, $10. The Port D Input Pins address is read-only, while the Data Register and the Data Direction Register are read/write.

DATA BUS

Port D Data Register – PORTD

Port D Data Direction Register – DDRD

Port D Input Pins Address – PIND

The Port D output buffers can sink 10 mA. As inputs, Port D pins that are externally pulled low will source current if the pull-up resistors are activated.

Bit 76543210

$12

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 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 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

PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 PORTD

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.

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

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 19. 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

Figure 35. Port D Schematic Diagram (Pins PD7 - PD0)

MOS PULLUP

RESET

PDn

WP:

WRITE PORTD

WD:

WRITE DDRD

RL:

READ PORTD LATCH

RP:

READ PORTD PIN

RD:

READ DDRD

n : 0 - 7

DDDn

RESET

PORTDn

DATA BUS

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Memory Programming

Program Memory Lock Bits

The ATtiny28 MCU provides two Lock bits that can be left unprogrammed (“1”) or can be programmed (“0”) to obtain the additional features listed in Table 20. The Lock bits can only be erased with the Chip Erase command.

Table 20. 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 is disabled.

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

Note: 1. Further programming of the Fuse bits is also disabled. Program the Fuse bits before

programming the Lock bits.

Fuse Bits The ATtiny28 has five Fuse bits, INTCAP and CKSEL3..0.

• When the INTCAP Fuse is programmed (“0”), internal load capacitors are

connected between XTAL1/XTAL2 and GND, similar to C1 and C2 in Figure 2. See

“Crystal Oscillator” on page 4. Default value is unprogrammed (“1”).

• CKSEL3..0 Fuses: See Table 1, “Device Clocking Option Select,” on page 4 and

Ta bl e 5 , “ATtiny28 Clock Options and Start-up Time,” on page 14, for which combination of CKSEL3..0 to use. Default value is “0010”, internal RC oscillator with long start-up time.

(1)

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

Signature Bytes All Atmel microcontrollers have a 3-byte signature code that identifies the device. The

three bytes reside in a separate address space.

For the ATtiny28, they are:

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

2. $001: $91 (indicates 2 KB Flash memory)

3. $002: $07 (indicates ATtiny28 device when signature byte $001 is $91)

Calibration Byte The ATtiny28 has one byte calibration value for the internal RC oscillator. This byte

resides in the high byte of address $000 in the signature address space. During memory programming, the external programmer must read this location, and program it into a selected location in the the normal Flash program memory. At start-up, the user software must read this Flash location and write the value to the OSCCAL register.

Programming the Flash Atmel’s ATtiny28 offers 2K bytes of Flash program memory.

The ATtiny28 is shipped with the on-chip Flash program memory array in the erased state (i.e., contents = $FF) and ready to be programmed. This device supports a highvoltage (12V) parallel programming mode. Only minor currents (<1mA) are drawn from the +12V pin during programming.

The program memory array in the ATtiny28 is programmed byte-by-byte. During programming, the supply voltage must be in accordance with Table 21.

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Table 21. Supply Voltage during Programming

Part Serial Programming Parallel Programming

ATtiny28 Not applicable 4.5 - 5.5V

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

bits and Fuse bits in the ATtiny28.

Signal Names In this section, some pins of the ATtiny28 are referenced by signal names describing

their function during parallel programming. See Figure 36 and Table 22. Pins not described in Table 22 are referenced by pin name.

The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse. The coding is shown in Table 23.

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

24.

Figure 36. Parallel Programming

RDY/BSY

XA0

XA1

+12V

PD1

PD2

PD3

PD4

PD5

PD6

RESET

XTAL1

GND

ATtiny28

VCC

PB7 - PB0

+5V

DATA

1062E–10/01

Table 22. Pin Name Mapping

Signal Name in

Programming Mode Pin Name I/O Function

RDY/BSY PD1 O

BS PD4 I

XA0 PD5 I XTAL1 Action Bit 0

XA1 PD6 I XTAL1 Action Bit 1

DATA PB7 - PB0 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)

Table 23. XA1 and XA0 Coding

XA1 XA0 Action when XTAL1 is Pulsed

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

1 0 Load Command

1 1 No Action, Idle

Load Flash/Signature byte Address (High or low address byte for Flash determined by BS)

Table 24. Command Byte Coding

is low)

Command Byte Command Executed

1000 0000 Chip Erase

0100 0000 Write Fuse Bits

0010 0000 Write Lock Bits

0001 0000 Write Flash

0000 1000 Read Signature Bytes and Calibration Byte

0000 0100 Read Fuse and Lock Bits

0000 0010 Read Flash

Enter Programming Mode The following algorithm puts the device in parallel programming mode:

1. Apply 4.5 - 5.5V between VCC and GND.

2. Set RESET and BS pins 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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Chip Erase The Chip Erase command will erase the Flash memory and the Lock bits. The Lock bits

are not reset until the Flash has been completely erased. The Fuse bits are not changed. Chip Erase must be performed before the Flash 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.

5. Give WR

6. Wait until RDY/BSY goes high before loading a new command.

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.

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 - $03).

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

a negative pulse. This starts the Chip Erase. RDY/BSY goes low.

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

goes low.

3. Wait until RDY/BSY

(See Figure 37 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.

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

goes high to program the next byte.

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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

(See Figure 38 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 to be loaded only once when writing or reading multiple

memory locations.

• Address high byte only needs to 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 after a Chip

Erase.

These considerations also apply to Flash and signature bytes reading.

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):

A: Load Command “0000 0010”.

B: Load Address High Byte ($00 - $03).

C: Load Address Low Byte ($00 - $FF).

1. Set OE

2. Set BS to “1”. The Flash word high byte can now be read from DATA.

3. Set OE to “1”.

to “0”, and BS to “0”. The Flash word low byte can now be read at DATA.

goes high to program the next byte.

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):

A: Load Command “0100 0000”.

D: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.

Bit 4 = INTCAP Fuse Bit 3 = CKSEL3 Fuse Bit 2 = CKSEL2 Fuse Bit 1 = CKSEL1 Fuse Bit 0 = CKSEL0 Fuse Bits 7 - 5 = “1”. These bits are reserved and should be left unprogrammed (“1”).

E: Write Data Low Byte.

Programming the Lock Bits The algorithm for programming the Lock bits is as follows (refer to “Programming the

Flash” for details on command and data loading):

A: Load Command “0010 0000”.

D: Load Data Low Byte. Bit n = “0” programs the Lock bit.

Bit 2 = Lock Bit2 Bit 1 = Lock Bit1 Bits 7 - 3,0 = “1”. These bits are reserved and should be left unprogrammed (“1”).

E: Write Data Low Byte.

The Lock bits can only be cleared by executing Chip Erase.

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Reading the Fuse and Lock Bits

Reading the Signature Bytes and Calibration Byte

The algorithm for reading the Fuse and Lock bits is as follows (refer to “Programming the Flash” for details on command loading):

A: Load Command “0000 0100”.

1. Set OE to “0”, and BS to “0”. The status of the Fuse bits can now be read at

DATA (“0” means programmed). Bit 4 = INTCAP Fuse Bit 3 = CKSEL3 Fuse Bit 2 = CKSEL2 Fuse Bit 1 = CKSEL1 Fuse Bit 0 = CKSEL0 Fuse

2. Set BS to “1”. The status of the Lock bits can now be read at DATA (“0” means

programmed). Bit 2: Lock Bit2 Bit 1: Lock Bit1

3. Set OE

to “1”.

The algorithm for reading the signature bytes and the calibration byte is as follows (refer to “Programming the Flash” for details on command and address loading):

A: Load Command “0000 1000”.

C: Load Address Low Byte ($00 - $02).

1. Set OE

to “0”, and BS to “0”. The selected signature byte can now be read at

DATA.

C: Load Address Low Byte ($00).

1. Set OE to “0”, and BS to “1”. The calibration byte can now be read at DATA.

2. Set OE to “1”.

Figure 37. Programming the Flash Waveforms

DATA

XA1

XA0

XTAL1

RDY/BSY

RESET

12V

$10 ADDR. HIGH ADDR. LOW DATA LOW

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Figure 38. Programming the Flash Waveforms (Continued)

DATA

XA1

XA0

XTAL1

RDY/BSY

RESET

DATA HIGH

+12V

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Parallel Programming Characteristics

Figure 39. Parallel Programming Timing

XLWL

DVXH

XHXL

XLDX

XLOL

BVWL

WLWH

WLRL

OLDV

RHBX

WLRH

OHDZ

XTAL1

Data & Contol

(DATA, XA0/1, BS)

RDY/BSY

DATA

Parallel Programming Characteristics

TA = 25°C ± 10%, VCC = 5V ± 10%

Symbol Parameter Min Typ Max Unit

DVXH

XHXL

XLDX

XLWL

BVWL

RHBX

WLWH

WLRL

WLRH

XLOL

OLDV

OHDZ

Programming Enable Voltage 11.5 12.5 V

Programming Enable Current 250.0 µA

Data & Control Valid before XTAL1 High 67.0 ns

XTAL1 Pulse Width High 67.0 ns

Data & 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 67.0 ns

WR Low to RDY/BSY Low 0.0 2.5 µs

WR Low to RDY/BSY High 0.5 0.7 0.9 ms

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

Write

Read

1062E–10/01

Electrical Characteristics

Absolute Maximum Ratings

Operating Temperature............................. -40°C to +85/105°C

Storage Temperature..................................... -65°C to +150°C

Voltage on Any Pin except RESET

with Respect to Ground.............................-1.0V to VCC + 0.5V

Maximum Operating Voltage ............................................ 6.0V

Voltage on RESET

with Respect to Ground ....-1.0V to +13.0V

DC Current per I/O Pin, except PA2 ........................... 40.0 mA

DC Current PA2 .......................................................... 60.0 mA

DC Current VCC and GND Pin................................. 300.0 mA

DC Characteristics

TA = -40°C to 85°C, VCC = 1.8V to 5.5V (unless otherwise noted)

Symbol Parameter Condition Min Typ Max Units

IL1

IH1

IH2

Input Low Voltage (Except XTAL) -0.5 0.3 Vcc

Input Low Voltage XTAL -0.5 0.1 Vcc

Input High Voltage (Except XTAL, RESET)0.6 V

Input High Voltage XTAL 0.7 V

Input High Voltage RESET 0.85 V

Output Low Voltage Por ts A, D

Output Low Voltage

(3)

= 20 mA, VCC = 5V

= 10 mA, VCC = 3V

= 25 mA, VCC = 2.0V

Por t A2

Output High Voltage Por ts A, D

(4)

= -3 mA, VCC = 5V

= -1.5 mA, VCC = 3V

Input Leakage Current I/O Pin VCC = 5.5V, pin low

(absolute value)

Input Leakage Current I/O Pin VCC = 5.5V, pin high

(absolute value)

*NOTICE: Stresses beyond those ratings listed under

“Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or other conditions beyond those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

(1)

(2)

VCC + 0.5 V

0.6

0.5

1.0

4.3

2.3

8.0 µA

V V

I/O

I/O Pin Pull-up 35.0 122.0 kΩ

Active Mode, VCC = 3V,

3.0 mA

4MHz

Idle Mode VCC = 3V,

1.0 1.2 mA

4MHz

Power Supply Current

Power-down

(5)

, VCC = 3V

9.0 15.0 µA

WDT enabled

Power-down

, VCC = 3V

<1.0 2.0 µA

(5)

WDT disabled

ATtiny28L/V

1062E–10/01

ATtiny28L/V

DC Characteristics (Continued)

TA = -40°C to 85°C, VCC = 1.8V to 5.5V (unless otherwise noted)

Symbol Parameter Condition Min Typ Max Units

ACLK

ACPD

ACIO

Analog Comparator Input Offset Voltage

Analog Comparator Input Leakage Current

Analog Comparator Propagation Delay

VCC = 5V

= VCC/2

VCC = 5V V

= VCC/2

VCC = 2.7V

= 4.0V

-50.0 50.0 nA

Notes: 1. “Max” means the highest value where the pin is guaranteed to be read as low.

2. “Min” means the lowest value where the pin is guaranteed to be read as high.

3. Although each I/O port can sink more than the test conditions (20 mA at VCC = 5V, 10 mA at VCC = 3V) under steady-state conditions (non-transient), the following must be observed: 1] The sum of all I 2] The sum of all I

exceeds the test condition, VOL may exceed the related specification.

If I

, for all ports, should not exceed 300 mA.

, for port D0 - D7 and XTAL2 should not exceed 100 mA.

Pins are not guaranteed to sink current greater than the listed test conditions.

4. Although each I/O port can source more than the test conditions (3 mA at VCC = 5V, 1.5 mA at VCC = 3V) under steady-state conditions (non-transient), the following must be observed: 1] The sum of all I 2] The sum of all I

exceeds the test condition, VOH may exceed the related specification.

If I

, for all ports, should not exceed 300 mA.

, for port D0 - D7 and XTAL2 should not exceed 100 mA.

Pins are not guaranteed to source current greater than the listed test conditions.

5. Minimum VCC for power-down is 1.5V.

750.0

500.0

40.0 mV

1062E–10/01

External Clock Drive Waveforms

Figure 40. External Clock

VIH1

VIL1

External Clock Drive

Symbol Parameter

1/t

CLCL

CHCX

CLCX

CLCH

CHCL

Oscillator Frequency 0.0 1.2 0.0 4.0 0.0 4.0 MHz

Clock Period 833.0 250.0 250.0 ns

High Time 333.0 100.0 100.0 ns

Low Time 333.0 100.0 100.0 ns

Rise Time 1.6 1.6 0.5 µs

Fall Time 1.6 1.6 0.5 µs

= 1.8V to 2.7V VCC = 2.7V to 4.0V VCC = 4.0V to 5.5V

UnitsMin Max Min Max Min Max

Table 25. External RC Oscillator, Typical Frequencies

R [kΩ] C [pF] f

100.0 70.0 100.0 kHz

31.5 20.0 1.0 MHz

6.5 20.0 4.0 MHz

Note: R should be in the range 3 - 100 kΩ, and C should be at least 20 pF.

ATtiny28L/V

1062E–10/01

ATtiny28L/V

Typical Characteristics

The following charts show typical behavior. These figures are not tested during manufacturing. All current consumption measurements are performed with all I/O pins configured as inputs and with internal pull-ups enabled. A sine wave generator with railto-rail output is used as clock source.

The power consumption in Power-down mode is independent of clock selection.

The current consumption is a function of several factors, such as: operating voltage, operating frequency, loading of I/O pins, switching rate of I/O pins, code executed and ambient temperature. The dominating factors are operating voltage and frequency. The current drawn from capacitive loaded pins may be estimated (for one pin) as C where C

= Load Capacitance, VCC = Operating Voltage and f = Average Switching Fre-

• VCC • f,

quency of I/O pin.

The parts are characterized at frequencies and voltages higher than test limits. Parts are not guaranteed to function properly at frequencies and voltages higher than the ordering code indicates.

The difference between current consumption in Power-down mode with Watchdog Timer enabled and Power-down mode with Watchdog Timer disabled represents the differential current drawn by the Watchdog Timer.

Figure 41. Active Supply Current vs. Frequency

ACTIVE SUPPLY CURRENT vs. FREQUENCY

= 25˚C

VCC = 6.0V

(mA)

VCC = 1.8V

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

VCC = 2.1V

Frequency (MHz)

VCC = 2.4V

VCC = 3.3V VCC = 3.0V

VCC = 2.7V

VCC = 3.6V

VCC = 5.5V

VCC = 5.0V

VCC = 4.5V

VCC = 4.0V

1062E–10/01

Figure 42. Active Supply Current vs. V

ACTIVE SUPPLY CURRENT vs. V

FREQUENCY = 4 MHz

(mA)

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

VCC (V)

TA = 25˚C

TA = 85˚C

Figure 43. Active Supply Current vs. VCC, Device Clocked by Internal Oscillator

ACTIVE SUPPLY CURRENT vs. V

DEVICE CLOCKED BY 1.2MHz INTERNAL RC OSCILLATOR

T = 25˚C

(mA)

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

(V)

T = 85˚C

ATtiny28L/V

1062E–10/01

ATtiny28L/V

Figure 44. Active Supply Current vs. VCC, Device Clocked by External 32 kHz Crystal

ACTIVE SUPPLY CURRENT vs. V

DEVICE CLOCKED BY 32 kHz CRYSTAL

3.5

2.5

(mA)

1.5

0.5

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

VCC (V)

Figure 45. Idle Supply Current vs. Frequency

IDLE SUPPLY CURRENT vs. FREQUENCY

4.5

3.5

TA = 25˚C

TA = 85˚C

VCC = 6.0V

VCC = 5.5V

VCC = 5.0V

1062E–10/01

2.5

(mA)

1.5

0.5

VCC = 1.8V

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

VCC = 2.1V

Frequency (MHz)

VCC = 2.4V

VCC = 2.7V

VCC = 3.6V VCC = 3.3V

VCC = 3.0V

VCC = 4.5V

VCC = 4.0V

Figure 46. Idle Supply Current vs. V

(mA)

IDLE SUPPLY CURRENT vs. V

FREQUENCY = 4 MHz

1.4

1.2

0.8

0.6

0.4

0.2

TA = 85˚C

TA = 25˚C

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

VCC (V)

Figure 47. Idle Supply Current vs. VCC, Device Clocked by Internal Oscillator

0.7

DEVICE CLOCKED BY 1.2MHz INTERNAL RC OSCILLATOR

IDLE SUPPLY CURRENT vs. V

0.6

T = 25˚C

0.5

0.4

(mA)

0.3

0.2

0.1

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

(V)

T = 85˚C

ATtiny28L/V

1062E–10/01

ATtiny28L/V

Figure 48. Idle Supply Current vs. VCC, Device Clocked by External 32 kHz Crystal

IDLE SUPPLY CURRENT vs. V

DEVICE CLOCKED BY 32 kHz CRYSTAL

(µA)

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

VCC (V)

Figure 49. Power-down Supply Current vs. V

POWER-DOWN SUPPLY CURRENT vs. V

WATCHDOG TIMER DISABLED

TA = 85˚C

TA = 25˚C

TA = 85˚C

2.5

(µA)

1.5

0.5

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

VCC (V)

TA = 70˚C

TA = 45˚C

TA = 25˚C

1062E–10/01

Figure 50. Power-down Supply Current vs. V

POWER-DOWN SUPPLY CURRENT vs. V

WATCHDOG TIMER ENABLED

(µA)

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

VCC (V)

TA = 25˚C

TA = 85˚C

Analog comparator offset voltage is measured as absolute offset.

Figure 51. Analog Comparator Offset Voltage vs. Common Mode Voltage (V

= 5V)

Offset Voltage (mV)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Common Mode Voltage (V)

TA = 25˚C

TA = 85˚C

ATtiny28L/V

1062E–10/01

ATtiny28L/V

Figure 52. Analog Comparator Offset Voltage vs. Common Mode Voltage (VCC = 2.7V)

TA = 25˚C

Offset Voltage (mV)

0 0.5 1 1.5 2 2.5 3

Common Mode Voltage (V)

Figure 53. Analog Comparator Input Leakage Current (V

(nA)

ACLK

TA = 85˚C

= 6V; TA = 25°C)

1062E–10/01

-10 0 0.5 1.51 2 2.5 3.53 4 4.5 5 6 6.5 75.5

VIN (V)

Figure 54. Calibrated Internal RC Oscillator Frequency vs. V

CALIBRATED RC OSCILLATOR FREQUENCY vs.

1.28

1.26

1.24

1.22

1.2

(MHz)

1.18

1.16

1.14

1.12

1.1

2 2.5 3 3.5 4 4.5 5 5.5 6

OPERATING VOLTAGE

(V)

Figure 55. Watchdog Oscillator Frequency vs. V

1600

T = 25˚C

T = 85˚C

T = 45˚C

T = 70˚C

1400

1200

1000

(kHz)

800

600

400

200

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

(V)

TA = 25˚C

TA = 85˚C

ATtiny28L/V

1062E–10/01

ATtiny28L/V

Sink and source capabilities of I/O ports are measured on one pin at a time.

Figure 56. Pull-up Resistor Current vs. Input Voltage (VCC = 5V)

120

100

(µA)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

TA = 25˚C

TA = 85˚C

VOP (V)

Figure 57. Pull-up Resistor Current vs. Input Voltage (V

TA = 25˚C

TA = 85˚C

= 2.7V)

1062E–10/01

(µA)

0 0.5 1 1.5 2 2.5 3

V (V)

Figure 58. I/O Pin Sink Current vs. Output Voltage. All pins except PA2 (VCC = 5V)

(mA)

0 0.5 1 1.5 2 2.5 3

TA = 25˚C

VOL (V)

Figure 59. I/O Pin Source Current vs. Output voltage (V

(mA)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

TA = 25˚C

TA = 85˚C

VOH (V)

TA = 85˚C

= 5V)

ATtiny28L/V

1062E–10/01

ATtiny28L/V

Figure 60. I/O Pin Sink Current vs. Output Voltage, All Pins Except PA2 (VCC = 2.7V)

(mA)

0 0.5 1 1.5 2

TA = 25˚C

TA = 85˚C

VOL (V)

Figure 61. I/O Pin Source Current vs. Output Voltage (V

TA = 25˚C

= 2.7V)

(mA)

0 0.5 1 1.5 2 2.5 3

TA = 85˚C

VOH (V)

1062E–10/01

Figure 62. PA2 I/O Pin Sink Current vs. Output Voltage (High Current Pin PA2; TA =

°C)

(mA)

0 0.5 1 1.5 2 2.5 3 3.5 4

VCC = 1.8V

(V)

Figure 63. I/O Pin Input Threshold Voltage vs. V

2.5

VCC = 2.4V

(TA = 25°C)

VCC = 3.6V

1.5

Threshold Voltage (V)

0.5

2.7 4.0 5.0

ATtiny28L/V

1062E–10/01

Figure 64. I/O Pin Input Hysteresis vs. VCC (TA = 25°C)

0.18

0.16

0.14

0.12

0.1

0.08

Input Hysteresis (V)

0.06

0.04

0.02

2.7 4.0 5.0

ATtiny28L/V

1062E–10/01

Register Summary

Address Name Bit 7Bit 6Bit 5Bit 4Bit 3Bit 2Bit 1Bit 0 Page

$3F SREG I T H S V N Z C page 11

$3E Reserved

... Reserved

$20 Reserved

$1F Reserved

$1E Reserved

$1D Reserved

$1C Reserved

$1B PORTA - - - - PORTA3 PORTA2 PORTA1 PORTA0 page 36

$1A PACR - - - - DDA3 PA2HC DDA1 DDA0 page 36

$19 PINA - - - -PINA3- PINA1 PINA0 page 37

$18 Reserved

$17 Reserved

$16 PINB PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 page 39

$15 Reserved

$14 Reserved

$13 Reserved

$12 PORTD PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 page 42

$11 DDRD DDD7 DDD6 DDD5 DDD4 DDD3 DDD2 DDD1 DDD0 page 42

$10 PIND PIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 page 42

$0F Reserved

$0E Reserved

$0D Reserved

$0C Reserved

$0B Reserved

$0A Reserved

$09 Reserved

$08 ACSR ACD - ACO ACI ACIE - ACIS1 ACIS0 page 34

$07 MCUCS PLUPB - SE SM WDRF - EXTRF PORF page 17

$06 ICR INT1 INT0 LLIE TOIE0 ISC11 ISC10 ISC01 ISC00 page 19

$05 IFR INTF1 INTF0 -TOV0- - - - page 20

$04 TCCR0 FOV0 - - OOM01 OOM00 CS02 CS01 CS00 page 24

$03 TCNT0 Timer/Counter0 (8-bit) page 25

$02 MODCR ONTIM4 ONTIM3 ONTIM2

$01 WDTCR - - - WDTOE WD E WDP2 WDP1 WDP0 page 26

$00 OSCCAL Oscillator Calibration Register page 28

Notes: 1. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses

should never be written.

2. 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 one back into any flag read as set, thus clearing the flag. The CBI and SBI instructions work with registers $00 to $1F only.

ONTIM1

ONTIM0 MCONF2 MCONF1 MCONF0 page 29

ATtiny28L/V

1062E–10/01

ATtiny28L/V

Instruction Set Summary

Mnemonic Operands Description Operation Flags # Clocks

ARITHMETIC AND LOGIC INSTRUCTIONS

ADD Rd, Rr Add Two Registers Rd ← Rd + Rr Z,C,N,V,H 1

ADC Rd, Rr Add with Carry Two Registers Rd ← Rd + Rr + C Z,C,N,V,H 1

SUB Rd, Rr Subtract Two Registers Rd ← Rd - Rr Z,C,N,V,H 1

SUBI Rd, K Subtract Constant from Register Rd ← Rd - K Z,C,N,V,H 1

SBC Rd, Rr Subtract with Carry Two Registers Rd ← Rd - Rr - C Z,C,N,V,H 1

SBCI Rd, K Subtract with Carry Constant from Reg. Rd ← Rd - K - C Z,C,N,V,H 1

AND Rd, Rr Logical AND Registers Rd ← Rd • Rr Z,N,V 1

ANDI Rd, K Logical AND Register and Constant Rd ← Rd • K Z,N,V 1

OR Rd, Rr Logical OR Registers Rd ← Rd v Rr Z,N,V 1

ORI Rd, K Logical OR Register and Constant Rd ← Rd v K Z,N,V 1

EOR Rd, Rr Exclusive OR Registers Rd ← Rd ⊕=Rr Z,N,V 1

COM Rd One’s Complement Rd ← $FF - Rd Z,C,N,V 1

NEG Rd Two’s Complement Rd ← $00 - Rd Z,C,N,V,H 1

SBR Rd, K Set Bit(s) in Register Rd ← Rd v K Z,N,V 1

CBR Rd, K Clear Bit(s) in Register Rd ← Rd • (FFh - K) Z,N,V 1

INC Rd Increment Rd ← Rd + 1 Z,N,V 1

DEC Rd Decrement Rd ← Rd - 1 Z,N,V 1

TST Rd Test for Zero or Minus Rd ← Rd •=Rd Z,N,V 1

CLR Rd Clear Register Rd ← Rd ⊕=Rd Z,N,V 1

SER Rd Set Register Rd ← $FF None 1

BRANCH INSTRUCTIONS

RJMP k Relative Jump PC ← PC + k + 1 None 2

RCALL k Relative Subroutine Call PC ← PC + k + 1 None 3

RET Subroutine Return PC ← STACK None 4

RETI Interrupt Return PC ← STACK I 4

CPSE Rd, Rr Compare, Skip if Equal if (Rd = Rr) PC ← PC + 2 or 3 None 1/ 2

CP Rd, Rr Compare Rd - Rr Z,N,V,C,H 1

CPC Rd, Rr Compare with Carry Rd - Rr - C Z,N,V,C,H 1

CPI Rd, K Compare Register with Immediate Rd - K Z N,V,C,H 1

SBRC Rr, b Skip if Bit in Register Cleared if (Rr(b) = 0) PC ← PC + 2 or 3 Non e 1/2

SBRS Rr, b Skip if Bit in Register is Set if (Rr(b) = 1) PC ← PC + 2 or 3 None 1/2

SBIC P, b Skip if Bit in I/O Register Cleared if (P(b) = 0) PC ← PC + 2 or 3 None 1/2

SBIS P, b Skip if Bit in I/O Register is Set if (P(b) = 1) PC ← PC + 2 or 3 None 1/2

BRBS s, k Branch if Status Flag Set if (SREG(s) = 1) then PC ← PC + k + 1 None 1/2

BRBC s, k Branch if Status Flag Cleared if (SREG(s) = 0) then PC ← PC + k + 1 None 1/2

BREQ k Branch if Equal if (Z = 1) then PC ← PC + k + 1 None 1/2

BRNE k Branch if Not Equal if (Z = 0) then PC ← PC + k + 1 None 1/2

BRCS k Branch if Carry Set if (C = 1) then PC ← PC + k + 1 None 1/2

BRCC k Branch if Carry Cleared if (C = 0) then PC ← PC + k + 1 None 1/2

BRSH k Branch if Same or Higher if (C = 0) then PC ← PC + k + 1 None 1/2

BRLO k Branch if Lower if (C = 1) then PC ← PC + k + 1 None 1/2

BRMI k Branch if Minus if (N = 1) then PC ← PC + k + 1 None 1/2

BRPL k Branch if Plus if (N = 0) then PC ← PC + k + 1 None 1/2

BRGE k Branch if Greater or Equal, Signed if (N ⊕ V = 0) then PC ← PC + k + 1 None 1/2

BRLT k Branch if Less than Zero, Signed if (N ⊕ V = 1) then PC ← PC + k + 1 None 1/2

BRHS k Branch if Half-carry Flag Set if (H = 1) then PC ← PC + k + 1 None 1/2

BRHC k Branch if Half-carry Flag Cleared if (H = 0) then PC ← PC + k + 1 None 1/2

BRTS k Branch if T-flag Set if (T = 1) then PC ← PC + k + 1 None 1/2

BRTC k Branch if T-flag Cleared if (T = 0) then PC ← PC + k + 1 None 1/2

BRVS k Branch if Overflow Flag is Set if (V = 1) then PC ← PC + k + 1 None 1/2

BRVC k Branch if Overflow Flag is Cleared if (V = 0) then PC ← PC + k + 1 None 1/2

BRIE k Branch if Interrupt Enabled if (I = 1) then PC ← PC + k + 1 None 1/2

BRID k Branch if Interrupt Disabled if (I = 0) then PC ← PC + k + 1 None 1/2

1062E–10/01

Instruction Set Summary (Continued)

Mnemonic Operands Description Operation Flags # Clocks

DATA TRANSFER INSTRUCTIONS

LD Rd, Z Load Register Indirect Rd ← (Z) None 2

ST Z, Rr Store Register Indirect (Z) ← Rr None 2

MOV Rd, Rr Move between Registers Rd ← Rr None 1

LDI Rd, K Load Immediate Rd =← KNone1

IN Rd, P In Port Rd ← PNone1

OUT P, Rr Out Port P ← Rr None 1

LPM Load Program Memory R0 ←=(Z) None 3

BIT AND BIT-TEST INSTRUCTIONS

SBI P, b Set Bit in I/O Register I/O(P,b) ← 1None2

CBI P, b Clear Bit in I/O Register I/O(P,b) ← 0None2

LSL Rd Logical Shift Left Rd(n+1) ← Rd(n), Rd(0) ← 0 Z,C,N,V 1

LSR Rd Logical Shift Right Rd(n) ← Rd(n+1), Rd(7) ← 0 Z,C,N,V 1

ROL Rd Rotate Left through Carry Rd(0) ← C, Rd(n+1) ← Rd(n), C ← Rd(7) Z,C,N,V 1

ROR Rd Rotate Right through Carry Rd(7) ← C, Rd(n) ← Rd(n+1), C ← Rd(0) Z,C,N,V 1

ASR Rd Arithmetic Shift Right Rd(n) ← Rd(n+1), n = 0..6 Z,C,N,V 1

SWAP Rd Swap Nibbles Rd(3..0) ← Rd(7..4), Rd(7..4) ← Rd(3..0) None 1

BSET s Flag Set SREG(s) ← 1 SREG(s) 1

BCLR s Flag Clear SREG(s) ← 0 SREG(s) 1

BST Rr, b Bit Store from Register to T T ← Rr(b) T 1

BLD Rd, b Bit Load from T to Register Rd(b) ← TNone1

SEC Set Carry C ← 1C1

CLC Clear Carry C ← 0C1

SEN Set Negative Flag N ←=1N1

CLN Clear Negative Flag N ← 0N1

SEZ Set Zero Flag Z ← 1Z1

CLZ Clear Zero Flag Z ← 0Z1

SEI Global Interrupt Enable I ← 1I1

CLI Global Interrupt Disable I ← 0I1

SES Set Signed Test Flag S ← 1S1

CLS Clear Signed Test Flag S ← 0S1

SEV Set Two’s Complement Overflow V=← 1V1

CLV Clear Two’s Complement Overflow V ← 0V1

SET Set T in SREG T=← 1T1

CLT Clear T in SREG T ←=0T1

SEH Set Half-carry Flag in SREG H ← 1H1

CLH Clear Half-carry Flag in SREG H ← 0H1

NOP No Operation None 1

SLEEP Sleep (see specific descr. for Sleep function) None 1

WDR Watchdog Reset (see specific descr. for WDR/timer) None 1

ATtiny28L/V

1062E–10/01

ATtiny28L/V

Ordering Information

Speed (MHz) Power Supply (Volts) Ordering Code Package Operation Range

4 2.7 - 5.5 ATtiny28L-4AC

ATtiny28L-4PC ATtiny28L-4MC

ATtiny28L-4AI ATtiny28L-4PI ATtiny28L-4MI

1.2 1.8 - 5.5 ATtiny28V-1AC

AT ti n y 28 V- 1 P C AT ti n y 28 V- 1 M C

AT ti n y 28 V- 1 A I AT ti n y 28 V- 1 P I AT ti n y 28 V- 1 M I

32A 28P3 32M1-A

Commercial

(0°C to 70°C)

Industrial

(-40°C to 85°C)

Commercial

(0°C to 70°C)

Industrial

(-40°C to 85°C)

Package Type

32A 32-lead, Thin (1.0 mm) Plastic Quad Flat Package (TQFP)

28P3 28-lead, 0.300" Wide, Plastic Dual Inline Package (PDIP)

32M1-A 32-pad, 5x5x1.0 body, Lead Pitch 0.50mm Micro Lead Frame Package (MLF)

1062E–10/01

Packaging Information

32A

32-lead, Thin (1.0mm) Plastic Quad Flatpack (TQFP), 7x7mm body, 2.0mm footprint, 0.8mm pitch. Dimensions in Millimeters and (Inches)* JEDEC STADARD MS-026 ABA

9.25 (0.364)

PIN 1 ID

0.45 (0.018)

0.30 (0.012) PIN 1

8.75 (0.344)

0.80 (0.0315) BSC

0.20 (0.008)

0.09 (0.004)

0º~7º

9.25 (0.364)

8.75 (0.344)

7.10 (0.280)

6.90 (0.272)

0.75 (0.030)

0.45 (0.018)

*Controlling dimensions: Millimeters

1.20 (0.047) MAX

0.15 (0.006)

0.05 (0.002)

ATtiny28L/V

1062E–10/01

28P3

ATtiny28L/V

28-lead, Plastic Dual Inline Package (PDIP), 0.300" Wide, (0.288" body width) Dimensions in Millimeters and (Inches)*

34.80(1.370)

34.54(1.360)

7.49(0.295)

7.11(0.280)

4.57(0.180)MAX

3.56(0.140)

3.05(0.120)

2.54(0.100)BSC

0.38(0.015)

0.56(0.022)

0.38(0.015)

1.65(0.065)

1.27(0.050)

8.26(0.325)

7.62(0.300)

0º~ 15º REF

10.20(0.400)MAX

1062E–10/01

*Controlling dimension: Inches

REV. A 04/11/2001

32M1-A

PIN #1 ID

1 2 3

TOP VIEW

PIN 1 ID

BOTTOM VIEW

NOTE 1. JEDEC STANDARD MO-220, Fig 2 (Anvil Singulation), VHHD-2

1 2 3

SIDE VIEW

SYMBOL

D1 4.75 BSC

E 5.00 BSC

E1 4.75 BSC

E2 1.25 - 3.25

e 0.50 BSC

L 0.30 0.40 0.50

0.08

COMMON DIMENSIONS

(*Unit of Measure = mm)

MIN

0.80 0.90 1.00

0.00 0.02 0.05

- 0.65 1.00

0.20 REF

0.18 0.23 0.30

5.00 BSCD

1.25 - 3.25

- - 0.60

- - 12º

NOM

MAX

NOTE

2325 Orchard Parkway

San Jose, CA 95131

ATtiny28L/V

TITLE

32M1-A, 32-pad, 5x5x1.0mm body, Lead Pitch 0.50mm

06/27/01

Mirco Lead Frame package (MLF)

DRAWING NO. REV

32M1-A

1062E–10/01

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Corporate Headquarters

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Other terms and product names may be the trademarks of others.

Printed on recycled paper.

1062E–10/01/xM

Rainbow Electronics ATtiny28L User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Features

Pin Configurations

Description The ATtiny28 is a low-power CMOS 8-bit microcontroller based on the AVR RISC archi-

Block Diagram Figure 1. The ATtiny28 Block Diagram

Pin Descriptions

Port A (PA3..PA0) Port A is a 4-bit I/O port. PA2 is output-only and can be used as a high-current LED

Port B (PB7..PB0) Port B is an 8-bit input port with internal pull-ups (selected for all Port B pins). Port B

Port D (PD7..PD0) Port D is an 8-bit I/O port. Port pins can provide internal pull-up resistors (selected for

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

XTAL2 Output from the inverting oscillator amplifier.

RESET

Clock Options The device has the following clock source options, selectable by Flash Fuse bits as

Internal RC Oscillator 0100 - 0010

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

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

External RC Oscillator For timing insensitive applications, the external RC configuration shown in Figure 4 can

Architectural Overview

General-purpose Register File

ALU – Arithmetic Logic Unit

Downloadable Flash Program Memory

Program and Data Addressing Modes

Register Indirect Figure 8. Indirect Register Addressing

Register Direct, Two Registers Rd and Rr

I/O Direct Figure 10. I/O Direct Addressing

Relative Program Addressing, RJMP and RCALL

Constant Addressing Using the LPM Instruction

Subroutine and Interrupt Hardware Stack

Memory Access and Instruction Execution Timing

I/O Memory The I/O space definition of the ATtiny28 is shown in Table 2.

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

Reset and Interrupt Handling

Reset Sources The ATtiny28 provides three sources of reset:

Power-on Reset A Power-on Reset (POR) pulse is generated by an on-chip detection circuit. The detec-

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 Control and Status Register – MCUCS

Interrupt Handling The ATtiny28 has one 8-bit Interrupt Control Register (ICR).

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

Interrupt Control Register – ICR

Interrupt Flag Register – IFR

External Interrupt The external interrupt is triggered by the INT pins. Observe that, if enabled, the interrupt

Low-level Input Interrupt The low-level interrupt is triggered by setting any of the Port B pins low. However, if any

Sleep Modes To enter the sleep modes, the SE bit in MCUCS must be set (one) and a SLEEP instruc-

Idle Mode When the SM bit is cleared (zero), the SLEEP instruction forces the MCU into the Idle

Power-down Mode When the SM bit is set (one), the SLEEP instruction forces the MCU into the Power-

Timer/Counter Prescaler Figure 20 shows the Timer/Counter prescaler.

TIMER/COUNTER0

Timer/Counter0 Control Register – TCCR0

Timer Counter 0 – TCNT0

Figure 22. Watchdog Timer

Watchdog Timer Control Register – WDTCR

Calibrated Internal RC Oscillator

Oscillator Calibration Register – OSCCAL

Hardware Modulator ATtiny28 features a built-in hardware modulator connected to a high-current output pad,

Modulation Control Register – MODCR

Analog Comparator The analog comparator compares the input values on the positive input PB0 (AIN0) and

Analog Comparator Control and Status Register – ACSR

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

Port A Port A is a 4-bit I/O port. PA2 is output-only, while PA3, PA1 and PA0 are bi-directional.

Port A Data Register – PORTA

Port A Control Register – PAC R

Port A as General Digital I/O PA3, PA1 and PA0 are general I/O pins. The DDAn (n: 3,1,0) bits in PACR select the

Port A Input Pins Address – PINA

Alternate Function of PA2 PA2 is the built-in, high-current LED driver and it is always an output pin. The output sig-

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

Port B Port B is an 8-bit input port.

Port B Input Pins Address – PINB

Port B as General Digital Input All eight pins in Port B have equal functionality when used as digital input pins.

Alternate Functions of Port B All Port B pins are connected to a low-level detector that can trigger the low-level input

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

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

Port D Data Register – PORTD

Port D Data Direction Register – DDRD

Port D Input Pins Address – PIND

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

Memory Programming