Microchip Technology Inc PIC16C84-04-P, PIC16C84-04-SO, PIC16C84-04I-P, PIC16C84-04I-SO, PIC16C84-10-P Datasheet
...
1997 Microchip Technology Inc. DS30445C-page 1
M
High Performance RISC CPU Features:
• Only 35 single word instructions to learn
• All instructions single cycle (400 ns @ 10 MHz)
except for program branches which are two-cycle
• Operating speed: DC - 10 MHz clock input
DC - 400 ns instruction cycle
• 14-bit wide instructions
• 8-bit wide data path
• 1K x 14 EEPROM program memory
• 36 x 8 general purpose registers (SRAM)
• 64 x 8 on-chip EEPROM data memory
• 15 special function hardware registers
• Eight-level deep hardware stack
• Direct, indirect and relative addressing modes
• Four interrupt sources:
- External RB0/INT pin
- TMR0 timer overflow
- PORTB<7:4> interrupt on change
- Data EEPROM write complete
• 1,000,000 data memory EEPROM
ERASE/WRITE cycles
• EEPROM Data Retention > 40 years
Peripheral Features:
• 13 I/O pins with individual direction control
• High current sink/source for direct LED drive
- 25 mA sink max. per pin
- 20 mA source max. per pin
• TMR0: 8-bit timer/counter with 8-bit
programmable prescaler
Special Microcontroller Features:
• Power-on Reset (POR)
• Power-up Timer (PWRT)
• Oscillator Start-up Timer (OST)
• Watchdog Timer (WDT) with its own on-chip RC
oscillator for reliable operation
• Code protection
• Power saving SLEEP mode
• Selectable oscillator options
• Serial In-System Programming - via two pins
Pin Diagram
CMOS Tec hnology:
• Low-power, high-speed CMOS EEPROM
technology
• Fully static design
• Wide operating voltage range:
- Commercial: 2.0V to 6.0V
- Industrial: 2.0V to 6.0V
• Low power consumption:
- < 2 mA typical @ 5V, 4 MHz
- 60 µ A typical @ 2V, 32 kHz
- 26 µ A typical standby current @ 2V
RA1
RA0
OSC1/CLKIN
OSC2/CLKOUT
V
DD
RB7
RB6
RB5
RB4
RA2
RA3
RA4/T0CKI
MCLR
VSS
RB0/INT
RB1
RB2
RB3
•1
2
3
4
5
6
7
8
9
18
17
16
15
14
13
12
11
10
PIC16C84
PDIP, SOIC
PIC16C84
8-bit CMOS EERPOM Microcontroller
PIC16C84
DS30445C-page 2
1997 Microchip Technology Inc.
Table of Contents
1.0 General Description....................................................................................................................................................................... 3
2.0 PIC16C84 Device Varieties ........................................................................................................................................................... 5
3.0 Architectural Overview................................................................................................................................................................... 7
4.0 Memory Organization................................................................................................................................................................... 11
5.0 I/O Ports.......................................................................................................................................................................................19
6.0 Timer0 Module and TMR0 Register.............................................................................................................................................25
7.0 Data EEPROM Memory...............................................................................................................................................................31
8.0 Special Features of the CPU ....................................................................................................................................................... 35
9.0 Instruction Set Summary.............................................................................................................................................................. 51
10.0 Development Support .................................................................................................................................................................. 67
11.0 Electrical Characteristics for PIC16C84....................................................................................................................................... 71
12.0 DC & AC Characteristics Graphs/Tables for PIC16C84 .............................................................................................................. 83
13.0 Packaging Information ................................................................................................................................................................. 97
Appendix A: Feature Improvements - From PIC16C5X To PIC16C84............................................................................................ 99
Appendix B: Code Compatibility - from PIC16C5X to PIC16C84.................................................................................................... 99
Appendix C: What’s New In This Data Sheet................................................................................................................................. 100
Appendix D: What’s Changed In This Data Sheet......................................................................................................................... 100
Appendix E: Conversion Considerations - PIC16C84 to PIC16F83/F84 And PIC16CR83/CR84.................................................. 101
Index .................................................................................................................................................................................................. 103
On-Line Support................................................................................................................................................................................. 105
PIC16C84 Product Identification System........................................................................................................................................... 107
Sales and Support.............................................................................................................................................................................. 107
To Our Valued Customers
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PIC16C84
1997 Microchip Technology Inc. DS30445C-page 3
1.0 GENERAL DESCRIPTION
The PIC16C84 is a low-cost, high-performance,
CMOS, fully-static, 8-bit microcontroller.
All PIC16/17 microcontrollers employ an advanced
RISC architecture. PIC16CXX devices have enhanced
core features, eight-lev el deep stack, and multiple internal and external interrupt sources. The separate
instruction and data buses of the Harvard architecture
allow a 14-bit wide instruction word with a separate
8-bit wide data bus. The two stage instruction pipeline
allows all instructions to execute in a single cycle,
except for program branches (which require two
cycles). A total of 35 instructions (reduced instruction
set) are available. Additionally, a large register set is
used to achieve a very high performance level.
PIC16CXX microcontrollers typically achieve a 2:1
code compression and up to a 2:1 speed improvement
(at 10 MHz) over other 8-bit microcontrollers in their
class.
The PIC16C84 has 36 bytes of RAM, 64 bytes of Data
EEPROM memory, and 13 I/O pins. A timer/counter is
also available.
The PIC16CXX family has special features to reduce
external components, thus reducing cost, enhancing
system reliability and reducing power consumption.
There are four oscillator options, of which the single pin
RC oscillator provides a low-cost solution, the LP
oscillator minimizes power consumption, XT is a
standard crystal, and the HS is for High Speed crystals.
The SLEEP (power-down) mode offers power savings.
The user can wake the chip from sleep through sev er al
external and internal interrupts and resets.
A highly reliable Watchdog Timer with its own on-chip
RC oscillator provides protection against software lockup.
The PIC16C84 EEPROM program memory allows the
same device package to be used for prototyping and
production. In-circuit reprogrammability allows the
code to be updated without the device being removed
from the end application. This is useful in the
development of many applications where the device
may not be easily accessible, but the prototypes may
require code updates. This is also useful for remote
applications where the code may need to be updated
(such as rate information).
Table 1-1 lists the features of the PIC16C84. A simplified block diagram of the PIC16C84 is shown in
Figure 3-1.
The PIC16C84 fits perfectly in applications ranging
from high speed automotive and appliance motor
control to low-power remote sensors, electronic locks,
security devices and smart cards. The EEPROM
technology makes customization of application
programs (transmitter codes, motor speeds, receiver
frequencies, security codes, etc.) extremely fast and
convenient. The small footprint packages make this
microcontroller series perfect for all applications with
space limitations. Low cost, low power, high
performance, ease of use and I/O flexibility make the
PIC16C84 very versatile even in areas where no
microcontroller use has been considered before
(e.g., timer functions, serial communication, capture
and compare, PWM functions and co-processor
applications).
The serial in-system programming feature (via two
pins) offers flexibility of customizing the product after
complete assembly and testing. This feature can be
used to serialize a product, store calibration data, or
program the device with the current firmware before
shipping.
1.1 F
amily and Upward Compatibility
Those users familiar with the PIC16C5X family of
microcontrollers will realize that this is an enhanced
version of the PIC16C5X architecture. Please refer to
Appendix A for a detailed list of enhancements. Code
written for PIC16C5X can be easily ported to the
PIC16C84 (Appendix B).
1.2 De
velopment Support
The PIC16CXX family is suppor ted by a full-featured
macro assembler, a software simulator, an in-circuit
emulator, a low-cost development programmer and a
full-featured programmer. A “C” compiler and fuzzy
logic support tools are also available.
PIC16C84
DS30445C-page 4
1997 Microchip Technology Inc.
TABLE 1-1 PIC16C8X FAMILY OF DEVICES
PIC16F83
PIC16CR83 PIC16F84 PIC16CR84
Clock
Maximum Frequency
of Operation (MHz)
10 10 10 10
Flash Program Memory 512 — 1K —
Memory
EEPROM Program Memory — — — —
ROM Program Memory — 512 — 1K
Data Memory (bytes) 36 36 68 68
Data EEPROM (bytes) 64 64 64 64
Peripherals Timer Module(s) TMR0 TMR0 TMR0 TMR0
Features
Interrupt Sources 4 4 4 4
I/O Pins 13 13 13 13
Voltage Range (Volts) 2.0-6.0 2.0-6.0 2.0-6.0 2.0-6.0
Packages 18-pin DIP,
SOIC
18-pin DIP,
SOIC
18-pin DIP,
SOIC
18-pin DIP,
SOIC
All PICmicro™ Family devices have Power-on Reset, selectable Watchdog Timer, selectable code protect and high I/O current capability. All PIC16C8X Family devices use serial programming with clock pin RB6 and data pin RB7.
PIC16C84
1997 Microchip Technology Inc. DS30445C-page 5
2.0 PIC16C84 DEVICE VARIETIES
A variety of frequency ranges and packaging options
are available . Depending on application and production
requirements the proper device option can be selected
using the information in this section. When placing
orders, please use the “PIC16C84 Product
Identification System” at the back of this data sheet to
specify the correct part number.
There are two device “types” as indicated in the device
number.
1. C , as in PIC16 C 84. These devices have
EEPROM program memory and operate over
the standard voltage range.
2. LC , as in PIC16 LC 84. These devices have
EEPROM program memory and operate over an
extended voltage range.
When discussing memory maps and other architectural
features, the use of C also implies the LC versions.
2.1 Electricall
y Erasable Devices
These devices are offered in the lower cost plastic
package, even though the device can be erased and
reprogrammed. This allows the same device to be used
for prototype development and pilot programs as well
as production.
A further advantage of the electrically erasable version
is that they can be erased and reprogrammed in-circuit,
or by device programmers, such as Microchip's
PICSTART
Plus or PRO MATE
II programmers.
PIC16C84
DS30445C-page 6
1997 Microchip Technology Inc.
NOTES:
PIC16C84
1997 Microchip Technology Inc. DS30445C-page 7
3.0 ARCHITECTURAL OVERVIEW
The high performance of the PIC16CXX family can be
attributed to a number of architectural features
commonly found in RISC microprocessors. To begin
with, the PIC16CXX uses a Harvard architecture. This
architecture has the program and data accessed from
separate memories. So the device has a program
memory bus and a data memory bus. This improves
bandwidth over traditional von Neumann architecture
where program and data are fetched from the same
memory (accesses over the same bus). Separating
program and data memory further allows instructions
to be sized differently than the 8-bit wide data word.
PIC16CXX opcodes are 14-bits wide, enabling single
word instructions. The full 14-bit wide program memory
bus fetches a 14-bit instruction in a single cycle. A twostage pipeline overlaps fetch and execution of instructions (Example 3-1). Consequently , all instructions e xecute in a single cycle (400 ns @ 10 MHz) except for
program branches.
The PIC16C84 addresses 1K x 14 program memory.
All program memory is internal.
PIC16CXX devices can directly or indirectly address its
register files or data memory. All special function
registers including the program counter are mapped in
the data memory. An orthogonal (symmetrical)
instruction set that makes it possible to carry out any
operation on any register using any addressing mode.
This symmetrical nature and lack of ‘special optimal
situations’ make programming with the PIC16CXX
simple yet efficient. In addition, the learning curve is
reduced significantly.
The PIC16C84 has 36 x 8 SRAM and 64 x 8 EEPROM
data memory.
PIC16CXX devices contain an 8-bit ALU and working
register. The ALU is a general pur pose ar ithmetic unit.
It performs arithmetic and Boolean functions between
data in the working register and any register file.
The ALU is 8-bits wide and capable of addition,
subtraction, shift and logical operations. Unless
otherwise mentioned, arithmetic operations are two's
complement in nature. In two-operand instructions,
typically one operand is the working register
(W register), and the other operand is a file register or
an immediate constant. In single operand instructions,
the operand is either the W register or a file register.
The W register is an 8-bit working register used for ALU
operations. It is not an addressable register.
Depending on the instruction executed, the ALU may
affect the values of the Carry (C), Digit Carry (DC), and
Zero (Z) bits in the STATUS register. The C and DC bits
operate as a borro
w and digit borrow out bit,
respectively, in subtraction. See the SUBLW and SUBWF
instructions for examples.
A simplified block diagram for the PIC16C84 is shown
in Figure 3-1, its corresponding pin description is
shown in Table 3-1.
PIC16C84
DS30445C-page 8
1997 Microchip Technology Inc.
FIGURE 3-1: PIC16C84 BLOCK DIAGRAM
EEPROM
Program
Memory
Program Counter
13
Program
Bus 14
Instruction reg
8 Level Stack
(13-bit)
Direct Addr
8
Instruction
Decode &
Control
Timing
Generation
OSC2/CLKOUT
OSC1/CLKIN
Power-up
Timer
Oscillator
Start-up Timer
Power-on
Reset
Watchdog
Timer
MCLR
VDD, VSS
W reg
ALU
MUX
I/O Ports
TMR0
STATUS reg
FSR reg
Indirect
Addr
RA3:RA0
RB7:RB1
RA4/T0CKI
EEADR
EEPROM
Data Memory
64 x 8
EEDATA
Addr Mux
RAM Addr
RAM
File Registers
EEPROM Data Memory
Data Bus 8
5
7
7
1K x 14
36 x 8
RB0/INT
PIC16C84
1997 Microchip Technology Inc. DS30445C-page 9
TABLE 3-1 PIC16C8X PINOUT DESCRIPTION
Pin Name
DIP
No.
SOIC
No.
I/O/P
Type
Buffer
Type
Description
OSC1/CLKIN 16 16 I ST/CMOS
(1)
Oscillator crystal input/external clock source input.
OSC2/CLKOUT 15 15 O — Oscillator crystal output. Connects to crystal or resonator in crys-
tal oscillator mode. In RC mode , OSC2 pin outputs CLK OUT which
has 1/4 the frequency of OSC1, and denotes the instruction cycle
rate.
MCLR
4 4 I/P ST Master clear (reset) input/programming voltage input. This pin is an
active low reset to the device.
PORTA is a bi-directional I/O port.
RA0 17 17 I/O TTL
RA1 18 18 I/O TTL
RA2 1 1 I/O TTL
RA3 2 2 I/O TTL
RA4/T0CKI 3 3 I/O ST Can also be selected to be the clock input to the TMR0 timer/
counter. Output is open drain type.
PORTB is a bi-directional I/O port. PORTB can be software pro-
grammed for internal weak pull-up on all inputs.
RB0/INT 6 6 I/O TTL RB0/INT can also be selected as an external interrupt pin.
RB1 7 7 I/O TTL
RB2 8 8 I/O TTL
RB3 9 9 I/O TTL
RB4 10 10 I/O TTL Interrupt on change pin.
RB5 11 11 I/O TTL Interrupt on change pin.
RB6 12 12 I/O TTL/ST
(2)
Interrupt on change pin. Serial programming clock.
RB7 13 13 I/O TTL/ST
(2)
Interrupt on change pin. Serial programming data.
V
SS
5 5 P — Ground reference for logic and I/O pins.
V
DD
14 14 P — Positive supply for logic and I/O pins.
Legend: I= input O = output I/O = Input/Output P = power
— = Not used TTL = TTL input ST = Schmitt Trigger input
Note 1: This buffer is a Schmitt Trigger input when configured in RC oscillator mode and a CMOS input otherwise.
2:
This buffer is a Schmitt Trigger input when used in serial programming mode.
PIC16C84
DS30445C-page 10
1997 Microchip Technology Inc.
3.1 Clocking Scheme/Instruction Cycle
The clock input (from OSC1) is internally divided by
four to generate four non-overlapping quadrature
clocks namely Q1, Q2, Q3 and Q4. Internally, the
program counter (PC) is incremented every Q1, the
instruction is fetched from the program memory and
latched into the instruction register in Q4. The
instruction is decoded and executed during the
following Q1 through Q4. The clocks and instruction
execution flow is shown in Figure 3-2.
3.2 Instruction Flow/Pipelining
An “Instruction Cycle” consists of four Q cycles (Q1,
Q2, Q3 and Q4). The instruction fetch and execute are
pipelined such that fetch takes one instruction cycle
while decode and execute takes another instruction
cycle. However, due to the pipelining, each instruction
effectively executes in one cycle. If an instruction
causes the program counter to change (e.g., GOTO )
then two cycles are required to complete the instruction
(Example 3-1).
A fetch cycle begins with the Program Counter (PC)
incrementing in Q1.
In the execution cycle, the f etched instruction is latched
into the “Instruction Register” in cycle Q1. This
instruction is then decoded and executed during the
Q2, Q3, and Q4 cycles. Data memory is read during Q2
(operand read) and written during Q4 (destination
write).
FIGURE 3-2: CLOCK/INSTRUCTION CYCLE
EXAMPLE 3-1: INSTRUCTION PIPELINE FLOW
Q1
Q2 Q3 Q4
Q1
Q2 Q3 Q4
Q1
Q2 Q3 Q4
OSC1
Q1
Q2
Q3
Q4
PC
OSC2/CLKOUT
(RC mode)
PC
PC+1 PC+2
Fetch INST (PC)
Execute INST (PC-1)
Fetch INST (PC+1)
Execute INST (PC)
Fetch INST (PC+2)
Execute INST (PC+1)
Internal
phase
clock
All instructions are single cycle, except for any program branches. These take two cycles since the fetch
instruction is “flushed” from the pipeline while the new instruction is being fetched and then executed.
1. MOVLW 55h
Fetch 1 Execute 1
2. MOVWF PORTB
Fetch 2 Execute 2
3. CALL SUB_1
Fetch 3 Execute 3
4. BSF PORTA, BIT3
Fetch 4 Flush
Fetch SUB_1 Execute SUB_1
PIC16C84
1997 Microchip Technology Inc. DS30445C-page 11
4.0 MEMORY ORGANIZATION
There are two memory blocks in the PIC16C84. These
are the program memory and the data memory. Each
block has its own bus , so that access to each b lock can
occur during the same oscillator cycle.
The data memory can further be broken down into the
general purpose RAM and the Special Function
Registers (SFRs). The operation of the SFRs that
control the “core” are described here. The SFRs used
to control the peripheral modules are described in the
section discussing each individual peripheral module.
The data memory area also contains the data
EEPROM memory . This memory is not directly mapped
into the data memory, but is indirectly mapped. That is
an indirect address pointer specifies the address of the
data EEPROM memory to read/write. The 64 bytes of
data EEPROM memory have the address range
0h-3Fh. More details on the EEPROM memory can be
found in Section 7.0.
4.1 Pr
ogram Memory Organization
The PIC16CXX has a 13-bit program counter capable
of addressing an 8K x 14 program memory space. For
the PIC16C84, only the first 1K x 14 (0000h-03FFh) are
physically implemented (Figure 4-1). Accessing a location above the physically implemented address will
cause a wraparound. For example, locations 20h,
420h, 820h, C20h, 1020h, 1420h, 1820h, and 1C20h
will be the same instruction.
The reset vector is at 0000h and the interrupt vector is
at 0004h.
FIGURE 4-1: PROGRAM MEMORY MAP
AND STACK
PC<12:0>
Stack Level 1
•
Stack Level 8
Reset Vector
Peripheral Interrupt Vector
•
•
User Memory
Space
CALL, RETURN
RETFIE, RETLW
13
0000h
0004h
1FFFh
3FFh
PIC16C84
DS30445C-page 12
1997 Microchip Technology Inc.
4.2 Data Memory Organization
The data memory is partitioned into two areas. The first
is the Special Function Registers (SFR) area, while the
second is the General Purpose Registers (GPR) area.
The SFRs control the operation of the device.
Portions of data memory are banked. This is for both
the SFR area and the GPR area. The GPR area is
banked to allow greater than 116 bytes of general
purpose RAM. The banked areas of the SFR are f or the
registers that control the peripheral functions. Banking
requires the use of control bits for bank selection.
These control bits are located in the STATUS Register.
Figure 4-2 shows the data memory map organization.
Instructions MOVWF and MOVF can move values from the
W register to any location in the register file (“F”), and
vice-versa.
The entire data memory can be accessed either
directly using the absolute address of each register file
or indirectly through the File Select Register (FSR)
(Section 4.5). Indirect addressing uses the present
value of the RP1:RP0 bits for access into the banked
areas of data memory.
Data memory is partitioned into two banks which
contain the general purpose registers and the special
function registers. Bank 0 is selected by clearing the
RP0 bit (STATUS<5>). Setting the RP0 bit selects
Bank 1. Each Bank extends up to 7Fh (128 bytes). The
first twelve locations of each Bank are reserved for the
Special Function Registers. The remainder are General Purpose Registers implemented as static RAM.
4.2.1 GENERAL PURPOSE REGISTER FILE
All devices have some amount of General Purpose
Register (GPR) area. Each GPR is 8 bits wide and is
accessed either directly or indirectly through the FSR
(Section 4.5).
The GPR addresses in bank 1 are mapped to
addresses in bank 0. As an example, addressing location 0Ch or 8Ch will access the same GPR.
4.2.2 SPECIAL FUNCTION REGISTERS
The Special Function Registers (Figure 4-2 and
Table 4-1) are used by the CPU and Peripheral
functions to control the device operation. These
registers are static RAM.
The special function registers can be classified into two
sets, core and peripheral. Those associated with the
core functions are described in this section. Those
related to the operation of the peripheral features are
described in the section for that specific feature.
FIGURE 4-2: REGISTER FILE MAP
File Address
00h
01h
02h
03h
04h
05h
06h
07h
08h
09h
0Ah
0Bh
0Ch
2Fh
30h
7Fh
80h
81h
82h
83h
84h
85h
86h
87h
88h
89h
8Ah
8Bh
8Ch
FFh
Bank 0
Bank 1
Indirect addr.
(1)
Indirect addr.
(1)
TMR0 OPTION
PCL
STATUS
FSR
PORTA
PORTB
EEDATA
EEADR
PCLATH
INTCON
36
General
Purpose
registers
(SRAM)
PCL
STATUS
FSR
TRISA
TRISB
EECON1
EECON2
(1)
PCLATH
INTCON
Mapped
in Bank 0
Unimplemented data memory location; read as '0'.
File Address
AFh
B0h
Note 1: Not a physical register.
(accesses)
PIC16C84
1997 Microchip Technology Inc. DS30445C-page 13
TABLE 4-1 REGISTER FILE SUMMARY
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Value on
Power-on
Reset
Value on all
other resets
(Note3)
Bank 0
00h INDF Uses contents of FSR to address data memory (not a physical register)
---- ---- ---- ----
01h TMR0 8-bit real-time clock/counter
xxxx xxxx uuuu uuuu
02h PCL Low order 8 bits of the Program Counter (PC)
0000 0000 0000 0000
03h STATUS
(2)
IRP RP1 RP0
TO
PD Z DC C
0001 1xxx 000q quuu
04h FSR Indirect data memory address pointer 0
xxxx xxxx uuuu uuuu
05h PORTA
— — — RA4/T0CKI RA3 RA2 RA1 RA0 ---x xxxx ---u uuuu
06h PORTB RB7 RB6 RB5 RB4 RB3 RB2 RB1 RB0/INT xxxx xxxx uuuu uuuu
07h Unimplemented location, read as '0' ---- ---- ---- ---08h EEDATA EEPROM data register xxxx xxxx uuuu uuuu
09h EEADR EEPROM address register xxxx xxxx uuuu uuuu
0Ah PCLATH
— — — Write buffer for upper 5 bits of the PC
(1)
---0 0000 ---0 0000
0Bh INTCON GIE EEIE T0IE INTE RBIE T0IF INTF RBIF 0000 000x 0000 000u
Bank 1
80h INDF Uses contents of FSR to address data memory (not a physical register) ---- ---- ---- ----
81h
OPTION_
REG
RBPU INTEDG T0CS T0SE PSA PS2 PS1 PS0
1111 1111 1111 1111
82h PCL Low order 8 bits of Program Counter (PC) 0000 0000 0000 0000
83h STATUS
(2)
IRP RP1 RP0 TO PD Z DC C 0001 1xxx 000q quuu
84h FSR Indirect data memory address pointer 0 xxxx xxxx uuuu uuuu
85h TRISA
— — — PORTA data direction register ---1 1111 ---1 1111
86h TRISB PORTB data direction register 1111 1111 1111 1111
87h
Unimplemented location, read as '0' ---- ---- ---- ---88h EECON1 — — — EEIF WRERR WREN WR RD ---0 x000 ---0 q000
89h EECON2 EEPROM control register 2 (not a physical register) ---- ---- ---- ---0Ah PCLATH — — — Write buffer for upper 5 bits of the PC
(1)
---0 0000 ---0 0000
0Bh INTCON GIE EEIE T0IE INTE RBIE T0IF INTF RBIF 0000 000x 0000 000u
Legend: x = unknown, u = unchanged. - = unimplemented read as '0', q = value depends on condition.
Note 1: The upper byte of the program counter is not directly accessible. PCLATH is a slave register for PC<12:8>. The contents
of PCLATH can be transferred to the upper b yte of the program counter, but the contents of PC<12:8> is nev er transf erred
to PCLATH.
2: The T
O and PD status bits in the STATUS register are not affected by a MCLR reset.
3: Other (non power-up) resets include: external reset through MCLR and the Watchdog Timer Reset.
PIC16C84
DS30445C-page 14 1997 Microchip Technology Inc.
4.2.2.1 STATUS REGISTER
The STATUS register contains the arithmetic status of
the ALU, the RESET status and the bank select bit for
data memory.
As with any register, the STATUS register can be the
destination for any instruction. If the STA TUS register is
the destination for an instruction that affects the Z, DC
or C bits, then the write to these three bits is disabled.
These bits are set or cleared according to device logic.
Furthermore, the T
O and PD bits are not writable.
Therefore, the result of an instruction with the STATUS
register as destination may be different than intended.
For example, CLRF STATUS will clear the upper-three
bits and set the Z bit. This leaves the STATUS register
as 000u u1uu (where u = unchanged).
Only the BCF, BSF, SWAPF and MOVWF instructions
should be used to alter the ST ATUS register (T ab le 9-2)
because these instructions do not affect any status bit.
FIGURE 4-3: STATUS REGISTER (ADDRESS 03h, 83h)
Note 1: The IRP and RP1 bits (STATUS<7:6>) are
not used by the PIC16C84 and should be
programmed as cleared. Use of these bits
as general purpose R/W bits is NOT
recommended, since this may affect
upward compatibility with future products.
Note 2: The C and DC bits operate as a borro
w
and digit borrow out bit, respectively, in
subtraction. See the SUBLW and SUBWF
instructions for examples.
Note 3: When the STATUS register is the
destination for an instruction that affects
the Z, DC or C bits, then the write to these
three bits is disabled. The specified bit(s)
will be updated according to device logic
R/W-0 R/W-0 R/W-0 R-1 R-1 R/W-x R/W-x R/W-x
IRP RP1 RP0
TO PD
Z DC C R = Readable bit
W = Writable bit
U = Unimplemented bit,
read as ‘0’
- n = Value at POR reset
bit7 bit0
bit 7: IRP: Register Bank Select bit (used for indirect addressing)
0 = Bank 0, 1 (00h - FFh)
1 = Bank 2, 3 (100h - 1FFh)
The IRP bit is not used by the PIC16C8X. IRP should be maintained clear.
bit 6-5: RP1:RP0: Register Bank Select bits (used for direct addressing)
00 = Bank 0 (00h - 7Fh)
01 = Bank 1 (80h - FFh)
10 = Bank 2 (100h - 17Fh)
11 = Bank 3 (180h - 1FFh)
Each bank is 128 bytes. Only bit RP0 is used by the PIC16C8X. RP1 should be maintained clear.
bit 4: TO: Time-out bit
1 = After power-up, CLRWDT instruction, or SLEEP instruction
0 = A WDT time-out occurred
bit 3: PD: Power-down bit
1 = After power-up or by the CLRWDT instruction
0 = By execution of the SLEEP instruction
bit 2: Z: Zero bit
1 = The result of an arithmetic or logic operation is zero
0 = The result of an arithmetic or logic operation is not zero
bit 1: DC: Digit carry/borro
w bit (for ADDWF and ADDLW instructions) (For borrow the polarity is reversed)
1 = A carry-out from the 4th low order bit of the result occurred
0 = No carry-out from the 4th low order bit of the result
bit 0: C: Carry/borro
w bit (for ADDWF and ADDLW instructions)
1 = A carry-out from the most significant bit of the result occurred
0 = No carry-out from the most significant bit of the result occurred
Note: For borro
w the polarity is reversed. A subtraction is executed by adding the two’s complement of
the second operand. For rotate (RRF, RLF) instructions, this bit is loaded with either the high or
low order bit of the source register.
PIC16C84
1997 Microchip Technology Inc. DS30445C-page 15
4.2.2.2 OPTION_REG REGISTER
The OPTION_REG register is a readable and writable
register which contains various control bits to configure
the TMR0/WDT prescaler, the external INT interrupt,
TMR0, and the weak pull-ups on PORTB.
FIGURE 4-4: OPTION_REG REGISTER (ADDRESS 81h)
Note: When the prescaler is assigned to
the WDT (PSA = '1'), TMR0 has a 1:1
prescaler assignment.
R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1 R/W-1
RBPU INTEDG T0CS T0SE PSA PS2 PS1 PS0 R = Readable bit
W = Writable bit
U = Unimplemented bit,
read as ‘0’
- n = Value at POR reset
bit7 bit0
bit 7: RBPU: PORTB Pull-up Enable bit
1 = PORTB pull-ups are disabled
0 = PORTB pull-ups are enabled (by individual port latch values)
bit 6: INTEDG: Interrupt Edge Select bit
1 = Interrupt on rising edge of RB0/INT pin
0 = Interrupt on falling edge of RB0/INT pin
bit 5: T0CS: TMR0 Clock Source Select bit
1 = Transition on RA4/T0CKI pin
0 = Internal instruction cycle clock (CLKOUT)
bit 4: T0SE: TMR0 Source Edge Select bit
1 = Increment on high-to-low transition on RA4/T0CKI pin
0 = Increment on low-to-high transition on RA4/T0CKI pin
bit 3: PSA: Prescaler Assignment bit
1 = Prescaler assigned to the WDT
0 = Prescaler assigned to TMR0
bit 2-0: PS2:PS0: Prescaler Rate Select bits
000
001
010
011
100
101
110
111
1 : 2
1 : 4
1 : 8
1 : 16
1 : 32
1 : 64
1 : 128
1 : 256
1 : 1
1 : 2
1 : 4
1 : 8
1 : 16
1 : 32
1 : 64
1 : 128
Bit Value TMR0 Rate WDT Rate
PIC16C84
DS30445C-page 16 1997 Microchip Technology Inc.
4.2.2.3 INTCON REGISTER
The INTCON register is a readable and writable
register which contains the various enable bits for all
interrupt sources.
FIGURE 4-5: INTCON REGISTER (ADDRESS 0Bh, 8Bh)
Note: Interrupt flag bits get set when an interrupt
condition occurs regardless of the state of
its corresponding enable bit or the global
enable bit, GIE (INTCON<7>).
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-x
GIE EEIE T0IE INTE RBIE T0IF INTF RBIF R = Readable bit
W = Writable bit
U = Unimplemented bit,
read as ‘0’
- n = Value at POR reset
bit7 bit0
bit 7: GIE: Global Interrupt Enable bit
1 = Enables all un-masked interrupts
0 = Disables all interrupts
Note: For the operation of the interrupt structure, please refer to Section 8.5.
bit 6: EEIE: EE Write Complete Interrupt Enable bit
1 = Enables the EE write complete interrupt
0 = Disables the EE write complete interrupt
bit 5: T0IE: TMR0 Overflow Interrupt Enable bit
1 = Enables the TMR0 interrupt
0 = Disables the TMR0 interrupt
bit 4: INTE: RB0/INT Interrupt Enable bit
1 = Enables the RB0/INT interrupt
0 = Disables the RB0/INT interrupt
bit 3: RBIE: RB Port Change Interrupt Enable bit
1 = Enables the RB port change interrupt
0 = Disables the RB port change interrupt
bit 2: T0IF: TMR0 overflow interrupt flag bit
1 = TMR0 has overflowed (must be cleared in software)
0 = TMR0 did not overflow
bit 1: INTF: RB0/INT Interrupt Flag bit
1 = The RB0/INT interrupt occurred
0 = The RB0/INT interrupt did not occur
bit 0: RBIF: RB Port Change Interrupt Flag bit
1 = When at least one of the RB7:RB4 pins changed state (must be cleared in software)
0 = None of the RB7:RB4 pins have changed state
PIC16C84
1997 Microchip Technology Inc. DS30445C-page 17
4.3 Program Counter: PCL and PCLATH
The Program Counter (PC) is 13-bits wide. The low
byte is the PCL register, which is a readable and
writable register. The high byte of the PC (PC<12:8>) is
not directly readable nor writable and comes from the
PCLATH register . The PCLATH (PC latch high) register
is a holding register for PC<12:8>. The contents of
PCLATH are transferred to the upper byte of the
program counter when the PC is loaded with a new
value. This occurs during a CALL, GOTO or a wr ite to
PCL. The high bits of PC are loaded from PCLATH as
shown in Figure 4-6.
FIGURE 4-6: LOADING OF PC IN
DIFFERENT SITUATIONS
4.3.1 COMPUTED GOTO
A computed GOT O is accomplished b y adding an offset
to the program counter (ADDWF PCL). When doing a
table read using a computed GOTO method, care
should be exercised if the table location crosses a PCL
memory boundary (each 256 word block). Refer to the
application note
“Implementing a Table Read”
(AN556).
4.3.2 PROGRAM MEMORY PAGING
The PIC16C84 has 1K of program memory. The CALL
and GOTO instructions have an 11-bit address range.
This 11-bit address range allows a branch within a 2K
program memory page size. For future PIC16CXX
program memory expansion, there must be another
two bits to specify the program memory page. These
paging bits come from the PCLATH<4:3> bits
(Figure 4-6). When doing a CALL or a GOTO instruction,
the user must ensure that these page bits
(PCLATH<4:3>) are programmed to the desired
program memory page. If a CALL instruction (or
interrupt) is executed, the entire 13-bit PC is “pushed”
onto the stack (see next section). Therefore, manipulation of the PCLATH<4:3> is not required for the return
instructions (which “pops” the PC from the stack).
4.4 Stack
The PIC16C84 has an 8 deep x 13-bit wide hardware
stack (Figure 4-1). The stack space is not part of either
program or data space and the stack pointer is not
readable or writable.
The entire 13-bit PC is “pushed” onto the stack when a
CALL instruction is executed or an interrupt is acknowledged. The stack is “popped” in the event of a RETURN,
RETLW or a RETFIE instruction execution. PCLATH is
not affected by a push or a pop operation.
The stack operates as a circular buffer. That is, after the
stack has been pushed eight times, the ninth push overwrites the value that was stored from the first push. The
tenth push overwrites the second push (and so on).
If the stack is effectively popped nine times, the PC
value is the same as the value from the first pop.
PC
12 8 7 0
5
PCLATH<4:0>
PCLATH
INST with PCL
as dest
ALU result
GOTO, CALL
Opcode <10:0>
8
PC
12 11 10 0
11
PCLATH<4:3>
PCH PCL
8 7
2
PCLATH
PCH PCL
Note: The PIC16C84 ignores the PCLATH<4:3>
bits, which are used for program memory
pages 1, 2 and 3 (0800h - 1FFFh). The use
of PCLATH<4:3> as general purpose R/W
bits is not recommended since this may
affect upward compatibility with future
products.
Note: There are no instruction mnemonics called
push or pop. These are actions that occur
from the execution of the CALL, RETURN,
RETLW, and RETFIE instructions, or the
vectoring to an interrupt address.
Note: There are no status bits to indicate stack
overflow or stack underflow conditions.
PIC16C84
DS30445C-page 18 1997 Microchip Technology Inc.
4.5 Indirect Addressing; INDF and FSR
Registers
The INDF register is not a physical register. Addressing INDF actually addresses the register whose
address is contained in the FSR register (FSR is a
pointer
). This is indirect addressing.
EXAMPLE 4-1: INDIRECT ADDRESSING
• Register file 05 contains the value 10h
• Register file 06 contains the value 0Ah
• Load the value 05 into the FSR register
• A read of the INDF register will return the value of
10h
• Increment the value of the FSR register by one
(FSR = 06)
• A read of the INDF register now will return the
value of 0Ah.
Reading INDF itself indirectly (FSR = 0) will produce
00h. Writing to the INDF register indirectly results in a
no-operation (although STATUS bits may be affected).
A simple program to clear RAM locations 20h-2Fh
using indirect addressing is shown in Example 4-2.
EXAMPLE 4-2: HOW TO CLEAR RAM
USING INDIRECT
ADDRESSING
movlw 0x20 ;initialize pointer
movwf FSR ; to RAM
NEXT clrf INDF ;clear INDF register
incf FSR ;inc pointer
btfss FSR,4 ;all done?
goto NEXT ;NO, clear next
CONTINUE
: ;YES, continue
An effective 9-bit address is obtained by concatenating
the 8-bit FSR register and the IRP bit (ST ATUS<7>), as
shown in Figure 4-7. However, IRP is not used in the
PIC16C84.
FIGURE 4-7: DIRECT/INDIRECT ADDRESSING
Direct Addressing
RP1 RP0 6
from opcode
0 IRP 7 (FSR) 0
Indirect Addressing
bank select location select
bank select location select
00 01 10 11
00h
7Fh
00h
0Bh
0Ch
2Fh
30h
7Fh
not used
Bank 0 Bank 1 Bank 2 Bank 3
Addresses
map back
to Bank 0
Data
Memory
not used
PIC16C84
1997 Microchip Technology Inc. DS30445C-page 19
5.0 I/O PORTS
The PIC16C84 has two ports, PORTA and PORTB.
Some port pins are multiplexed with an alternate function for other features on the device.
5.1 PORTA and TRISA Registers
PORTA is a 5-bit wide latch. RA4 is a Schmitt Trigger
input and an open drain output. All other RA port pins
have TTL input levels and full CMOS output drivers. All
pins have data direction bits (TRIS registers) which can
configure these pins as output or input.
Setting a TRISA bit (=1) will make the corresponding
PORTA pin an input, i.e., put the corresponding output
driver in a hi-impedance mode. Clearing a TRISA bit
(=0) will make the corresponding PORTA pin an output,
i.e., put the contents of the output latch on the selected
pin.
Reading the PORTA register reads the status of the pins
whereas writing to it will write to the port latch. All write
operations are read-modify-write operations. So a write
to a port implies that the port pins are first read, then this
value is modified and written to the port data latch.
The RA4 pin is multiplexed with the TMR0 clock input.
FIGURE 5-1: BLOCK DIAGRAM OF PINS
RA3:RA0
EXAMPLE 5-1: INITIALIZING PORTA
CLRF PORTA ; Initialize PORTA by
; setting output
; data latches
BSF STATUS, RP0 ; Select Bank 1
MOVLW 0x0F ; Value used to
; initialize data
; direction
MOVWF TRISA ; Set RA<3:0> as inputs
; RA4 as outputs
; TRISA<7:5> are always
; read as '0'.
FIGURE 5-2: BLOCK DIAGRAM OF PIN RA4
Note: I/O pins have protection diodes to VDD and VSS.
Data
bus
Q
D
Q
CK
QD
Q
CK
Q D
EN
P
N
WR
Port
WR
TRIS
Data Latch
TRIS Latch
RD TRIS
RD PORT
TTL
input
buffer
VSS
VDD
I/O pin
Note: For crystal oscillator configurations
operating below 500 kHz, the device may
generate a spurious internal Q-clock when
PORTA<0> switches state. This does not
occur with an external clock in RC mode.
To avoid this, the RA0 pin should be kept
static, i.e. in input/output mode, pin RA0
should not be toggled.
Data
bus
WR
PORT
WR
TRIS
RD PORT
Data Latch
TRIS Latch
RD TRIS
Schmitt
Trigger
input
buffer
N
V
SS
RA4 pin
TMR0 clock input
Note: I/O pin has protection diodes to V
SS only.
QD
Q
CK
QD
Q
CK
EN
Q D
EN
PIC16C84
DS30445C-page 20 1997 Microchip Technology Inc.
TABLE 5-1 PORTA FUNCTIONS
TABLE 5-2 SUMMARY OF REGISTERS ASSOCIATED WITH PORTA
Name Bit0 Buffer Type Function
RA0 bit0 TTL Input/output
RA1 bit1 TTL Input/output
RA2 bit2 TTL Input/output
RA3 bit3 TTL Input/output
RA4/T0CKI bit4 ST Input/output or external clock input for TMR0.
Output is open drain type.
Legend: TTL = TTL input, ST = Schmitt Trigger input
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Value on
Power-on
Reset
Value on all
other resets
05h PORT A
— — — RA4/T0CKI RA3 RA2 RA1 RA0 ---x xxxx ---u uuuu
85h TRISA — — — TRISA4 TRISA3 TRISA2 TRISA1 TRISA0 ---1 1111 ---1 1111
Legend: x = unknown, u = unchanged, - = unimplemented read as '0'. Shaded cells are unimplemented, read as '0'
PIC16C84
1997 Microchip Technology Inc. DS30445C-page 21
5.2 PORTB and TRISB Registers
PORTB is an 8-bit wide bi-directional port. The
corresponding data direction register is TRISB. A '1' on
any bit in the TRISB register puts the corresponding
output driver in a hi-impedance mode. A '0' on any bit
in the TRISB register puts the contents of the output
latch on the selected pin(s).
Each of the PORTB pins have a weak internal pull-up.
A single control bit can turn on all the pull-ups. This is
done by clearing the RBPU
(OPTION_REG<7>) bit.
The weak pull-up is automatically turned off when the
port pin is configured as an output. The pull-ups are
disabled on a Power-on Reset.
Four of PORTB’s pins, RB7:RB4, have an interrupt on
change feature. Only pins configured as inputs can
cause this interrupt to occur (i.e., any RB7:RB4 pin
configured as an output is excluded from the interrupt
on change comparison). The pins value in input mode
are compared with the old value latched on the last
read of PORTB. The “mismatch” outputs of the pins are
OR’ed together to generate the RB port
change interrupt.
FIGURE 5-3: BLOCK DIAGRAM OF PINS
RB7:RB4
This interrupt can wake the device from SLEEP. The
user, in the interrupt service routine, can clear the
interrupt in the following manner:
a) Read (or write) PORTB. This will end the mis-
match condition.
b) Clear flag bit RBIF.
A mismatch condition will continue to set the RBIF bit.
Reading PORTB will end the mismatch condition, and
allow the RBIF bit to be cleared.
This interrupt on mismatch feature, together with
software configurable pull-ups on these four pins allow
easy interface to a key pad and make it possible for
wake-up on key-depression (see AN552 in the
Embedded Control Handbook).
The interrupt on change feature is recommended for
wake-up on key depression operation and operations
where PORTB is only used for the interrupt on change
feature. Polling of PORTB is not recommended while
using the interrupt on change feature.
FIGURE 5-4: BLOCK DIAGRAM OF PINS
RB3:RB0
Data Latch
From other
RBPU
(1)
P
V
DD
I/O
QD
CK
QD
CK
Q D
EN
Q D
EN
Data bus
WR Port
WR TRIS
Set RBIF
TRIS Latch
RD TRIS
RD Port
RB7:RB4 pins
weak
pull-up
RD Port
Latch
TTL
Input
Buffer
Note 1: TRISB = '1' enables weak pull-up
(if RBPU
= '0' in the OPTION_REG register).
2: I/O pins have diode protection to V
DD and VSS.
pin
(2)
Note 1: If a change on the I/O pin should occur
when a read operation of PORTB is being
executed (start of the Q2 cycle), the RBIF
interrupt flag bit may not be set.
RBPU
(1)
Note 1: TRISB = '1' enables weak pull-up
(if RBPU
= '0' in the OPTION_REG register).
2: I/O pins have diode protection to V
DD and VSS.
Data Latch
P
V
DD
QD
CK
QD
CK
Q D
EN
Data bus
WR Port
WR TRIS
RD TRIS
RD Port
weak
pull-up
RD Port
RB0/INT
TRIS Latch
TTL
Input
Buffer
I/O
pin
(2)
PIC16C84
DS30445C-page 22 1997 Microchip Technology Inc.
EXAMPLE 5-1: INITIALIZING PORTB
CLRF PORTB ; Initialize PORTB by
; setting output
; data latches
BSF STATUS, RP0 ; Select Bank 1
MOVLW 0xCF ; Value used to
; initialize data
; direction
MOVWF TRISB ; Set RB<3:0> as inputs
; RB<5:4> as outputs
; RB<7:6> as inputs
TABLE 5-3 PORTB FUNCTIONS
TABLE 5-4 SUMMARY OF REGISTERS ASSOCIATED WITH PORTB
Name Bit Buffer Type I/O Consistency Function
RB0/INT bit0 TTL Input/output pin or external interrupt input. Internal software
programmable weak pull-up.
RB1 bit1 TTL Input/output pin. Internal software programmable weak pull-up.
RB2 bit2 TTL Input/output pin. Internal software programmable weak pull-up.
RB3 bit3 TTL Input/output pin. Internal software programmable weak pull-up.
RB4 bit4 TTL Input/output pin (with interrupt on change). Internal software programma-
ble weak pull-up.
RB5 bit5 TTL Input/output pin (with interrupt on change). Internal software programma-
ble weak pull-up.
RB6 bit6 TTL/ST
(1)
Input/output pin (with interrupt on change). Internal software programma-
ble weak pull-up. Serial programming clock.
RB7 bit7 TTL/ST
(1)
Input/output pin (with interrupt on change). Internal software programma-
ble weak pull-up. Serial programming data.
Legend: TTL = TTL input, ST = Schmitt Trigger.
Note 1: This buffer is a Schmitt Trigger input when used in serial programming mode.
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Value on
Power-on
Reset
Value on all
other resets
06h PORTB RB7 RB6 RB5 RB4 RB3 RB2 RB1 RB0/INT xxxx xxxx uuuu uuuu
86h TRISB TRISB7 TRISB6 TRISB5 TRISB4 TRISB3 TRISB2 TRISB1 TRISB0 1111 1111 1111 1111
81h
OPTION_
REG
RBPU
INTEDG T0CS T0SE PSA PS2 PS1 PS0
1111 1111 1111 1111
Legend: x = unknown, u = unchanged. Shaded cells are not used by PORTB.
PIC16C84
1997 Microchip Technology Inc. DS30445C-page 23
5.3 I/O Programming Considerations
5.3.1 BI-DIRECTIONAL I/O PORTS
Any instruction which writes, operates internally as a
read followed by a write operation. The BCF and BSF
instructions, for example, read the register into the
CPU, ex ecute the bit operation and write the result back
to the register. Caution must be used when these
instructions are applied to a port with both inputs and
outputs defined. For example, a BSF operation on bit5
of PORTB will cause all eight bits of PORTB to be read
into the CPU. Then the BSF operation takes place on
bit5 and PORTB is written to the output latches. If
another bit of PORTB is used as a bi-directional I/O pin
(i.e., bit0) and it is defined as an input at this time, the
input signal present on the pin itself would be read into
the CPU and rewritten to the data latch of this particular
pin, overwriting the previous content. As long as the pin
stays in the input mode, no problem occurs. However,
if bit0 is switched into output mode later on, the content
of the data latch is unknown.
Reading the port register, reads the values of the port
pins. Wr iting to the por t register wr ites the value to the
port latch. When using read-modify-write instructions
(i.e., BCF, BSF , etc.) on a port, the value of the port pins
is read, the desired operation is done to this value, and
this value is then written to the port latch.
A pin actively outputting a Low or High should not be
driven from external devices at the same time in order
to change the level on this pin (“wired-or”, “wired-and”).
The resulting high output current may damage the chip.
5.3.2 SUCCESSIVE OPERATIONS ON I/O PORTS
The actual write to an I/O port happens at the end of an
instruction cycle, whereas for reading, the data must be
valid at the beginning of the instruction cycle (Figure 5-
5). Therefore , care must be e x ercised if a write follo wed
by a read operation is carried out on the same I/O port.
The sequence of instructions should be such that the
pin voltage stabilizes (load dependent) before the next
instruction which causes that file to be read into the
CPU is executed. Otherwise, the previous state of that
pin may be read into the CPU rather than the new state .
When in doubt, it is better to separate these instructions with a NOP or another instruction not accessing
this I/O port.
Example 5-1 shows the effect of two sequential readmodify-write instructions (e.g., BCF, BSF, etc.) on an
I/O port.
EXAMPLE 5-1: READ-MODIFY-WRITE
INSTRUCTIONS ON AN
I/O PORT
;Initial PORT settings: PORTB<7:4> Inputs
; PORTB<3:0> Outputs
;PORTB<7:6> have external pull-ups and are
;not connected to other circuitry
;
; PORT latch PORT pins
; ---------- -------- BCF PORTB, 7 ; 01pp ppp 11pp ppp
BCF PORTB, 6 ; 10pp ppp 11pp ppp
BSF STATUS, RP0 ;
BCF TRISB, 7 ; 10pp ppp 11pp ppp
BCF TRISB, 6 ; 10pp ppp 10pp ppp
;
;Note that the user may have expected the
;pin values to be 00pp ppp. The 2nd BCF
;caused RB7 to be latched as the pin value
;(high).
FIGURE 5-5: SUCCESSIVE I/O OPERATION
PC PC + 1 PC + 2
PC + 3
Q1 Q2
Q3
Q4
Q1 Q2
Q3
Q4
Q1 Q2
Q3
Q4
Q1 Q2
Q3
Q4
Instruction
fetched
RB7:RB0
MOVWF PORTB
write to
PORTB
NOP
Port pin
sampled here
NOP
MOVF PORTB,W
Instruction
executed
MOVWF PORTB
write to
PORTB
NOP
MOVF PORTB,W
PC
TPD
Note:
This example shows a write to PORTB
followed by a read from PORTB.
Note that:
data setup time = (0.25TCY - TPD)
where TCY = instruction cycle
TPD = propagation delay
Therefore, at higher clock frequencies,
a write followed by a read may be
problematic.
PIC16C84
DS30445C-page 24 1997 Microchip Technology Inc.
NOTES:
1997 Microchip Technology Inc. DS30445C-page 25
PIC16C84
6.0 TIMER0 MODULE AND TMR0
REGISTER
The Timer0 module timer/counter has the following
features:
• 8-bit timer/counter
• Readable and writable
• 8-bit software programmable prescaler
• Internal or external clock select
• Interrupt on overflow from FFh to 00h
• Edge select for external clock
Timer mode is selected by clearing the T0CS bit
(OPTION<5>). In timer mode, the Timer0 module
(Figure 6-1) will increment every instruction cycle
(without prescaler). If the TMR0 register is written, the
increment is inhibited for the following two cycles
(Figure 6-2 and Figure 6-3). The user can w ork around
this by writing an adjusted value to the TMR0 register.
Counter mode is selected by setting the T0CS bit
(OPTION<5>). In this mode TMR0 will increment either
on every rising or falling edge of pin RA4/T0CKI. The
incrementing edge is determined by the T0 source
edge select bit, T0SE (OPTION<4>). Clearing bit T0SE
selects the rising edge. Restrictions on the external
clock input are discussed in detail in Section 6.2.
The prescaler is shared between the Timer0 Module
and the Watchdog Timer. The prescaler assignment is
controlled, in software, by control bit PSA
(OPTION<3>). Clearing bit PSA will assign the
prescaler to the Timer0 Module. The prescaler is not
readable or writable. When the prescaler (Section 6.3)
is assigned to the Timer0 Module, the prescale value
(1:2, 1:4, ..., 1:256) is software selectable.
6.1 TMR0 Interrupt
The TMR0 interrupt is generated when the TMR0
register overflows from FFh to 00h. This overflow sets
the T0IF bit (INTCON<2>). The interrupt can be
masked by clearing enable bit T0IE (INTCON<5>). The
T0IF bit must be cleared in software by the Timer0
Module interrupt service routine before re-enabling this
interrupt. The TMR0 interrupt (Figure 6-4) cannot wake
the processor from SLEEP since the timer is shut off
during SLEEP.
FIGURE 6-1: TMR0 BLOCK DIAGRAM
FIGURE 6-2: TMR0 TIMING: INTERNAL CLOCK/NO PRESCALER
Note 1: Bits T0CS, T0SE, PS2, PS1, PS0 and PSA are located in the OPTION register.
2: The prescaler is shared with the Watchdog Timer (Figure 6-6)
RA4/T0CKI
T0SE
0
1
1
0
pin
T0CS
FOSC/4
Programmable
Prescaler
Sync with
Internal
clocks
TMR0 register
PSout
(2 cycle delay)
PSout
Data bus
8
Set bit T0IF
on Overflow
PSA
PS2, PS1, PS0
3
PC-1
Q1 Q2 Q3 Q4
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
PC
Instruction
Fetch
TMR0
PC PC+1 PC+2
PC+3
PC+4
PC+5 PC+6
T0
T0+1 T0+2 NT0 NT0 NT0
NT0+1 NT0+2
T0
MOVWF TMR0
MOVF TMR0,W
MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W
Write TMR0
executed
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0 + 1
Read TMR0
reads NT0 + 2
Instruction
Executed
PIC16C84
DS30445C-page 26 1997 Microchip Technology Inc.
FIGURE 6-3: TMR0 TIMING: INTERNAL CLOCK/PRESCALE 1:2
FIGURE 6-4: TMR0 INTERRUPT TIMING
PC-1
Q1 Q2 Q3 Q4
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
PC
Instruction
Fetch
TMR0
PC PC+1 PC+2 PC+3 PC+4 PC+5 PC+6
T0 NT0+1
MOVWF TMR0
MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W
Write TMR0
executed
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0 + 1
T0+1
NT0
Instruction
Execute
Q2Q1 Q3 Q4Q2Q1 Q3 Q4 Q2Q1 Q3 Q4 Q2Q1 Q3 Q4 Q2Q1 Q3 Q4
1
1
OSC1
CLKOUT
(3)
TMR0 timer
T0IF bit
(INTCON<2>)
FEh
GIE bit
(INTCON<7>)
INSTR
UCTION FLOW
PC
Instruction
fetched
PC
PC +1 PC +1 0004h
0005h
Instruction
executed
Inst (PC)
Inst (PC-1)
Inst (PC+1)
Inst (PC)
Inst (0004h) Inst (0005h)
Inst (0004h)Dummy cycle Dummy cycle
FFh 00h 01h 02h
Note 1: T0IF interrupt flag is sampled here (every Q1).
2: Interrupt latency = 3.25Tcy, where Tcy = instruction cycle time.
3: CLKOUT is available only in RC oscillator mode.
4
Interrupt Latency
(2)
4: The timer clock (after the synchronizer circuit) which increments the timer from FFh to 00h immediately sets the T0IF bit.
The TMR0 register will roll over 3 Tosc cycles later.
1997 Microchip Technology Inc. DS30445C-page 27
PIC16C84
6.2 Using TMR0 with External Clock
When an external clock input is used for TMR0, it must
meet certain requirements. The external clock
requirement is due to internal phase clock (T
OSC)
synchronization. Also, there is a delay in the actual
incrementing of the TMR0 register after
synchronization.
6.2.1 EXTERNAL CLOCK SYNCHRONIZATION
When no prescaler is used, the external clock input is
the same as the prescaler output. The synchronization
of pin RA4/T0CKI with the internal phase clocks is
accomplished by sampling the prescaler output on the
Q2 and Q4 cycles of the internal phase clocks
(Figure 6-5). Therefore, it is necessary for T0CKI to be
high for at least 2Tosc (plus a small RC delay) and low
for at least 2Tosc (plus a small RC delay). Refer to the
electrical specification of the desired device.
When a prescaler is used, the external clock input is
divided by an asynchronous ripple counter type
prescaler so that the prescaler output is symmetrical.
For the external clock to meet the sampling
requirement, the ripple counter must be taken into
account. Therefore, it is necessary for T0CKI to have a
period of at least 4T osc (plus a small RC dela y) divided
by the prescaler value. The only requirement on T0CKI
high and low time is that they do not violate the
minimum pulse width requirement of 10 ns. Refer to
parameters 40, 41 and 42 in the AC Electrical
Specifications of the desired device.
6.2.2 TMR0 INCREMENT DELAY
Since the prescaler output is synchronized with the
internal clocks, there is a small delay from the time the
external clock edge occurs to the time the Timer0
Module is actually incremented. Figure 6-5 shows the
delay from the external clock edge to the timer
incrementing.
6.3 Prescaler
An 8-bit counter is available as a prescaler for the
Timer0 Module, or as a postscaler for the Watchdog
Timer (Figure 6-6). For simplicity, this counter is being
referred to as “prescaler” throughout this data sheet.
Note that there is only one prescaler available which is
mutually exclusive between the Timer0 Module and the
Watchdog Timer. Thus, a prescaler assignment for the
Timer0 Module means that there is no prescaler for the
Watchdog Timer , and vice-versa.
The PSA and PS2:PS0 bits (OPTION<3:0>) determine
the prescaler assignment and prescale ratio.
When assigned to the Timer0 Module, all instructions
writing to the Timer0 Module (e.g., CLRF 1, MOVWF 1,
BSF 1,x ....etc.) will clear the prescaler. When
assigned to WDT, a CLRWDT instruction will clear the
prescaler along with the Watchdog Timer. The
prescaler is not readable or writable.
FIGURE 6-5: TIMER0 TIMING WITH EXTERNAL CLOCK
Increment TMR0 (Q4)
Ext. Clock Input or
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
TMR0
T0 T0 + 1 T0 + 2
Ext. Clock/Prescaler
Output After Sampling
(Note 3)
Note 1:
2:
3:
Delay from clock input change to TMR0 increment is 3Tosc to 7Tosc. (Duration of Q = Tosc).
Therefore, the error in measuring the interval between two edges on TMR0 input = ± 4Tosc max.
External clock if no prescaler selected, Prescaler output otherwise.
The arrows ↑ indicate where sampling occurs. A small clock pulse may be missed by sampling.
Prescaler Out (Note 2)
PIC16C84
DS30445C-page 28 1997 Microchip Technology Inc.
FIGURE 6-6: BLOCK DIAGRAM OF THE TMR0/WDT PRESCALER
RA4/T0CKI
T0SE
pin
M
U
X
CLKOUT (= Fosc/4)
SYNC
2
Cycles
TMR0 register
8-bit Prescaler
8 - to - 1MUX
M
U
X
M U X
Watchdog
Timer
PSA
0
1
0
1
WDT
time-out
PS2:PS0
8
Note: T0CS, T0SE, PSA, PS2:PS0 are bits in the OPTION register.
PSA
WDT Enable bit
M
U
X
0
1
0
1
Data Bus
Set bit T0IF
on overflow
8
PSA
T0CS
1997 Microchip Technology Inc. DS30445C-page 29
PIC16C84
6.3.1 SWITCHING PRESCALER ASSIGNMENT
The prescaler assignment is fully under software
control (i.e., it can be changed “on the fly” during
program execution).
Note: To avoid an unintended device RESET, the
following instruction sequence
(Example 6-1) must be executed when
changing the prescaler assignment from
Timer0 to the WDT. This sequence m ust be
taken even if the WDT is disabled. To
change prescaler from the WDT to the
Timer0 module use the sequence shown in
Example 6-2.
EXAMPLE 6-1: CHANGING PRESCALER
(TIMER0→WDT)
BCF STATUS, RP0 ;Bank 0
CLRF TMR0 ;Clear TMR0
; and Prescaler
BSF STATUS, RP0 ;Bank 1
CLRWDT ;Clears WDT
MOVLW b'xxxx1xxx' ;Select new
MOVWF OPTION ; prescale value
BCF STATUS, RP0 ;Bank 0
EXAMPLE 6-2: CHANGING PRESCALER
(WDT→TIMER0)
CLRWDT ;Clear WDT and
; prescaler
BSF STATUS, RP0 ;Bank 1
MOVLW b'xxxx0xxx' ;Select TMR0, new
; prescale value
’ and clock source
MOVWF OPTION ;
BCF STATUS, RP0 ;Bank 0
TABLE 6-1 REGISTERS ASSOCIATED WITH TIMER0
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Value on
Power-on
Reset
Value on all
other resets
01h TMR0 Timer0 module’s register xxxx xxxx uuuu uuuu
0Bh INTCON GIE
EEIE T0IE INTE RBIE T0IF INTF RBIF 0000 000x 0000 0000
81h OPTION
RBPU INTEDG T0CS T0SE PSA PS2 PS1 PS0 1111 1111 1111 1111
85h TRISA — — — TRISA4 TRISA3 TRISA2 TRISA1 TRISA0 ---1 1111 ---1 1111
Legend: x = unknown, u = unchanged. - = unimplemented read as '0'. Shaded cells are not associated with Timer0.
PIC16C84
DS30445C-page 30 1997 Microchip Technology Inc.
NOTES:
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