MICROCHIP PIC12C5XX User Manual
PIC12C5XX
8-Pin, 8-Bit CMOS Microcontroller
Devices included in this Data Sheet:
• PIC12C508 • PIC12C508A
• PIC12C509 • PIC12C509A
Note: Throughout this data sheet PIC12C508(A)
refers to the PIC12C508 and PIC12C508A.
PIC12C509(A) refers to the PIC12C509
and PIC12C509A. PIC12C5XX refers to
the PIC12C508, PIC12C508A, PIC12C509
and PIC12C509A.
High-Performance RISC CPU:
• Only 33 single word instructions to learn
• All instructions are single cycle (1 µ s) except for
program branches which are two-cycle
• Operating speed: DC - 4 MHz clock input
DC - 1 µ s instruction cycle
Device EPROM RAM
PIC12C508 512 x 12 25
PIC12C508A 512 x 12 25
PIC12C509 1024 x 12 41
PIC12C509A 1024 x 12 41
• 12-bit wide instructions
• 8-bit wide data path
• Seven special function hardware registers
• Two-level deep hardware stack
• Direct, indirect and relative addressing modes for
data and instructions
• Internal 4 MHz RC oscillator with programmable
calibration
• In-circuit serial programming
Peripheral Features:
• 8-bit real time clock/counter (TMR0) with 8-bit
programmable prescaler
• Power-On Reset (POR)
• Device Reset Timer (DRT)
• Watchdog Timer (WDT) with its own on-chip RC
oscillator for reliable operation
• Programmable code-protection
• Power saving SLEEP mode
• Wake-up from SLEEP on pin change
• Internal weak pull-ups on I/O pins
• Internal pull-up on MCLR
• Selectable oscillator options:
- INTRC: Internal 4 MHz RC oscillator
pin
- EXTRC: External low-cost RC oscillator
- XT: Standard crystal/resonator
- LP: Power saving, low frequency crystal
CMOS Tec hnology:
• Low power, high speed CMOS EPROM
technology
• Fully static design
• Wide operating voltage range
• Wide temperature range:
- Commercial: 0 ° C to +70 ° C
- Industrial: -40 ° C to +85 ° C
- Extended: -40 ° C to +125 ° C
• Low power consumption
- < 2 mA @ 5V, 4 MHz
- 15 µ A typical @ 3V, 32 KHz
- < 1 µ A typical standby current
Pin Diagram
PDIP, SOIC, Windowed Ceramic Side Brazed
PIC12C508(A
VDD
GP5/OSC1/CLKIN
GP4/OSC2
GP3/MCLR
/VPP
1
2
3
4
PIC12C509(A)
8
7
6
5
)
VSS
GP0
GP1
GP2/T0CKI
1998 Microchip Technology Inc. DS40139D-page 1
PIC12C5XX
Device Differences
Device
PIC12C508A 3.0-5.5 See Note 1 6 0.7
PIC12LC508A 2.5-5.5 See Note 1 6 0.7
PIC12C508 2.5-5.5 See Note 1 4 0.9
PIC12C509A 3.0-5.5 See Note 1 6 0.7
PIC12LC509A 2.5-5.5 See Note 1 6 0.7
PIC12C509 2.5-5.5 See Note 1 4 0.9
Note 1: If you change from the PIC12C50X to the PIC12C50XA, please verify oscillator characteristics in your appli-
cation.
Note 2: See Section 7.2.5 for OSCCAL implementation differences.
Voltage
Range
Oscillator
Oscillator
Calibration
(Bits)
2
Process
Technology
(Microns)
DS40139D-page 2
1998 Microchip Technology Inc.
PIC12C5XX
TABLE OF CONTENTS
1.0 General Description......................................................................................................................................................................4
2.0 PIC12C5XX Device Varieties.......................................................................................................................................................7
3.0 Architectural Overview .................................................................................................................................................................9
4.0 Memory Organization................................................................................................................................................................ 13
5.0 I/O Port...................................................................................................................................................................................... 21
6.0 Timer0 Module and TMR0 Register.......................................................................................................................................... 23
7.0 Special Features of the CPU..................................................................................................................................................... 27
8.0 Instruction Set Summary........................................................................................................................................................... 39
9.0 Development Support................................................................................................................................................................ 51
10.0 Electrical Characteristics - PIC12C508/PIC12C509/PIC12LC508/PIC12LC509 ...................................................................... 57
11.0 DC and AC Characteristics - PIC12C508/PIC12C509/PIC12LC508/PIC12LC509................................................................... 73
12.0 Electrical Characteristics - PIC12C508A/PIC12C509A/PIC12LC508A/PIC12LC509A............................................................. 77
13.0 DC and AC Characteristics - PIC12C508A/PIC12C509A/PIC12LC508A/PIC12LC509A......................................................... 91
14.0 Packaging Information............................................................................................................................................................... 95
INDEX................................................................................................................................................................................................ 101
PIC12C5XX Product Identification System........................................................................................................................................ 105
To Our Valued Customers
Most Current Data Sheet
To obtain the most up-to-date version of this data sheet, please check our Worldwide Web site at:
http://www.microchip.com
You can determine the version of a data sheet by examining its literature number found on the bottom outside corner of any page.
The last character of the literature number is the version number. e.g., DS30000A is version A of document DS30000.
Errata
An errata sheet may exist for current devices, describing minor operational differences (from the data sheet) and recommended
workarounds. As de vice/documentation issues become known to us , we will publish an err ata sheet. The err ata will specify the revision of silicon and revision of document to which it applies.
To determine if an errata sheet exists for a particular device, please check with one of the following:
• Microchip’s Worldwide Web site; http://www.microchip.com
• Your local Microchip sales office (see last page)
• The Microchip Corporate Literature Center; U.S. FAX: (602) 786-7277
When contacting a sales office or the literature center, please specify which device, revision of silicon and data sheet (include literature number) you are using.
Corrections to this Data Sheet
We constantly strive to improve the quality of all our products and documentation. We have spent a great deal of time to ensure
that this document is correct. How e ver, we realize that w e may have missed a fe w things . If you find any information that is missing
or appears in error, please:
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We appreciate your assistance in making this a better document.
1998 Microchip Technology Inc. DS40139D-page 3
PIC12C5XX
1.0 GENERAL DESCRIPTION
The PIC12C5XX from Microchip Technology is a family
of low-cost, high performance, 8-bit, fully static,
EPROM/ROM-based CMOS microcontrollers. It
employs a RISC architecture with only 33 single word/
single cycle instructions. All instructions are single
cycle (1 µ s) except for program branches which take
two cycles. The PIC12C5XX delivers perfor mance an
order of magnitude higher than its competitors in the
same price category. The 12-bit wide instructions are
highly symmetrical resulting in 2:1 code compression
over other 8-bit microcontrollers in its class. The easy
to use and easy to remember instruction set reduces
development time significantly.
The PIC12C5XX products are equipped with special
features that reduce system cost and power requirements. The Power-On Reset (POR) and Device Reset
Timer (DRT) eliminate the need for external reset circuitry. There are four oscillator configurations to choose
from, including INTRC internal oscillator mode and the
power-saving LP (Low Power) oscillator mode. Power
saving SLEEP mode, Watchdog Timer and code
protection features also improve system cost, power
and reliability.
The PIC12C5XX are available in the cost-effective
One-Time-Programmable (OTP) versions which are
suitable for production in any volume. The customer
can take full advantage of Microchip’s price leadership
in OTP microcontrollers while benefiting from the O TP’s
flexibility .
The PIC12C5XX products are supported by a full-featured macro assembler, a software simulator, an in-circuit emulator, a ‘C’ compiler, fuzzy logic support tools,
a low-cost development programmer, and a full featured programmer. All the tools are supported on IBM
PC and compatible machines.
1.1 Applications
The PIC12C5XX series fits perfectly in applications
ranging from personal care appliances and security
systems to low-power remote transmitters/receivers.
The EPROM technology makes customizing application programs (transmitter codes, appliance settings,
receiver frequencies, etc.) extremely fast and convenient. The small footprint packages, f or through hole or
surface mounting, make this microcontroller series perfect for applications with space limitations. Low-cost,
low-power, high performance, ease of use and I/O flexibility make the PIC12C5XX series very versatile even
in areas where no microcontroller use has been
considered before (e.g., timer functions, replacement
of “glue” logic and PLD’s in larger systems, coprocessor applications).
DS40139D-page 4
1998 Microchip Technology Inc.
TABLE 1-1: PIC12CXXX & PIC12CEXXX FAMILY OF DEVICES
PIC12C509(A) PIC12CE518 PIC12CE519 PIC12C671 PIC12C672 PIC12CE673 PIC12CE674
8-pin DIP,
JW, SOIC
8-pin DIP,
JW, SOIC
8-pin DIP,
JW, SOIC
8-pin DIP,
JW, SOIC
Clock
Memory
Peripherals
Features
PIC12C508(A)
Maximum
Frequency
of Operation
(MHz)
EPROM
Program
Memory
RAM Data
Memory
(bytes)
EEPROM
Data Memory
(bytes)
Timer
Module(s)
A/D Converter (8-bit)
Channels
Wake-up
from SLEEP
on pin
change
Interrupt
Sources
I/O Pins 5 5 5 5 5 5 5 5
Input Pins 1 1 1 1 1 1 1 1
Internal
Pull-ups
In-Circuit
Serial
Programming
Number of
Instructions
Packages 8-pin DIP,
4 4 4 4 10 10 10 10
512 x 12 1024 x 12 512 x 12 1024 x 12 1024 x 14 2048 x 14 1024 x 14 2048 x 14
25 41 25 41 128 128
— — 16 16 — —
TMR0 TMR0 TMR0 TMR0 TMR0 TMR0 TMR0 TMR0
— — — — 4 4 4 4
Yes Yes Yes Yes Yes Yes Yes Yes
— — 4 4 4 4
Yes Yes Yes Yes Yes Yes Yes Yes
Yes Yes Yes Yes Yes Yes Yes Yes
33 33 33 33 35 35 35 35
JW, SOIC
PIC12C5XX
128 128
16 16
8-pin DIP,
JW, SOIC
8-pin DIP, JW8-pin DIP,
JW
All PIC12CXXX & PIC12CEXXX devices have Power-on Reset, selectable Watchdog Timer, selectable
code protect and high I/O current capability.
All PIC12CXXX & PIC12CEXXX devices use serial programming with data pin GP0 and clock pin GP1.
1998 Microchip Technology Inc. DS40139D-page 5
PIC12C5XX
NOTES:
DS40139D-page 6
1998 Microchip Technology Inc.
PIC12C5XX
2.0 PIC12C5XX DEVICE VARIETIES
A variety of 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 PIC12C5XX Product
Identification System at the back of this data sheet to
specify the correct part number.
2.1 UV Erasab
The UV erasable version, offered in ceramic side
brazed package, is optimal for prototype development
and pilot programs.
The UV erasable version can be erased and
reprogrammed to any of the configuration modes.
Note: Please note that erasing the device will
also erase the pre-programmed internal
calibration value for the internal oscillator.
The calibration value must be saved prior
to erasing the part.
Microchip's PICSTART
grammers all support programming of the PIC12C5XX.
Third party programmers also are available; ref er to the
Microchip
Third Party Guide
le Devices
PLUS and PRO MATE
for a list of sources.
pro-
2.3 Quic
k-Turnaround-Production (QTP)
Devices
Microchip offers a QTP Programming Service for
factory production orders. This service is made
available for users who choose not to program a
medium to high quantity of units and whose code
patterns have stabilized. The devices are identical to
the OTP devices b ut with all EPROM locations and fuse
options already programmed by the factory. Certain
code and prototype verification procedures do apply
before production shipments are av ailable . Please contact your local Microchip Technology sales office for
more details.
2.4 Serializ
Production (SQTP
Microchip offers a unique programming service where
a few user-defined locations in each device are
programmed with different serial numbers. The serial
numbers may be random, pseudo-random or
sequential.
Serial programming allows each device to have a
unique number which can serve as an entry-code,
password or ID number.
ed Quick-Turnaround
SM
vices
) De
2.2 One-Time-Pr
ogrammable (OTP)
Devices
The availability of OTP devices is especially useful for
customers who need the flexibility for frequent code
updates or small volume applications.
The OTP devices , packaged in plastic pac kages permit
the user to program them once. In addition to the
program memory, the configuration bits must also be
programmed.
1998 Microchip Technology Inc. DS40139D-page 7
PIC12C5XX
NOTES:
DS40139D-page 8
1998 Microchip Technology Inc.
PIC12C5XX
3.0 ARCHITECTURAL OVERVIEW
The high performance of the PIC12C5XX family can
be attributed to a number of architectural features
commonly found in RISC microprocessors. To begin
with, the PIC12C5XX uses a Harvard architecture in
which program and data are accessed on separate
buses. This improves bandwidth over traditional von
Neumann architecture where program and data are
fetched on the same bus. Separating program and
data memory further allows instructions to be sized
differently than the 8-bit wide data word. Instruction
opcodes are 12-bits wide making it possible to have all
single word instructions. A 12-bit wide program
memory access bus fetches a 12-bit instruction in a
single cycle. A two-stage pipeline overlaps fetch and
execution of instructions. Consequently, all instructions
(33) execute in a single cycle (1 µ s @ 4MHz) except for
program branches.
The table below lists program memory (EPROM) and
data memory (RAM) for each PIC12C5XX device.
Device EPROM RAM
PIC12C508 512 x 12 25
PIC12C508A 512 x 12 25
PIC12C509 1024 x 12 41
PIC12C509A 1024 x 12 41
The PIC12C5XX can directly or indirectly address its
register files and data memory. All special function
registers including the program counter are mapped in
the data memory. The PIC12C5XX has a highly
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 PIC12C5XX simple yet efficient.
In addition, the learning curve is reduced significantly.
The PIC12C5XX device contains an 8-bit ALU and
working register. The ALU is a general purpose
arithmetic 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 W (working) register. The
other operand is either 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 borr
respectively, in subtraction. See the SUBWF and ADDWF
instructions for examples.
A simplified block diagram is shown in Figure 3-1, with
the corresponding device pins described in Table 3-1.
ow and digit borrow out bit,
1998 Microchip Technology Inc. DS40139D-page 9
PIC12C5XX
FIGURE 3-1: PIC12C5XX BLOCK DIAGRAM
OSC1/CLKIN
OSC2
Program
Bus
EPROM
512 x 12 or
1024 x 12
Program
Memory
12
Instruction reg
Instruction
Decode &
Control
Timing
Generation
Internal RC
OSC
12
Program Counter
STACK1
STACK2
Direct Addr
8
Device Reset
Timer
Power-on
Reset
Watchdog
Timer
MCLR
Vdd, Vss
RAM Addr
5
Data Bus
Addr MUX
3
8
RAM
25 x 8 or
41 x 8
File
Registers
9
5-7
FSR reg
STATUS reg
MUX
ALU
W reg
Timer0
8
Indirect
Addr
GPIO
GP0
GP1
GP2/T0CKI
GP3/MCLR/Vpp
GP4/OSC2
GP5/OSC1/CLKIN
DS40139D-page 10
1998 Microchip Technology Inc.
TABLE 3-1: PIC12C5XX PINOUT DESCRIPTION
PIC12C5XX
Name
GP0 7 7 I/O TTL/ST Bi-directional I/O port/ serial programming data. Can
GP1 6 6 I/O TTL/ST Bi-directional I/O port/ serial programming clock. Can
GP2/T0CKI 5 5 I/O ST Bi-directional I/O port. Can be configured as T0CKI.
GP3/MCLR
GP4/OSC2 3 3 I/O TTL Bi-directional I/O port/oscillator crystal output. Con-
GP5/OSC1/CLKIN 2 2 I/O TTL/ST Bidirectional IO port/oscillator crystal input/external
V
DD
SS
V
Legend: I = input, O = output, I/O = input/output, P = power, — = not used, TTL = TTL input,
ST = Schmitt Trigger input
/V
PP
DIP
Pin #
SOIC
Pin #
4 4 I TTL/ST Input port/master clear (reset) input/programming volt-
1 1 P — Positive supply for logic and I/O pins
8 8 P — Ground reference for logic and I/O pins
I/O/P
Type
Buffer
Type
Description
be software programmed for internal weak pull-up and
wake-up from SLEEP on pin change. This buffer is a
Schmitt Trigger input when used in serial programming
mode.
be software programmed for internal weak pull-up and
wake-up from SLEEP on pin change. This buffer is a
Schmitt Trigger input when used in serial programming
mode.
age input. When configured as MCLR
active low reset to the device. Voltage on MCLR
must not exceed V
or the device will enter programming mode. Can be
software programmed for internal weak pull-up and
wake-up from SLEEP on pin change. Weak pull-up
always on if configured as MCLR
mode.
nections to crystal or resonator in crystal oscillator
mode (XT and LP modes only, GPIO in other modes).
clock source input (GPIO in Internal RC mode only,
OSC1 in all other oscillator modes). TTL input when
GPIO, ST input in external RC oscillator mode.
DD
during normal device operation
, this pin is an
/V
PP
. ST when in MCLR
1998 Microchip Technology Inc. DS40139D-page 11
PIC12C5XX
3.1 Cloc
king Scheme/Instruction Cycle
The clock input (OSC1/CLKIN pin) is internally divided
by four to generate four non-overlapping quadrature
clocks namely Q1, Q2, Q3 and Q4. Internally, the
program counter is incremented every Q1, and the
instruction is fetched from program memory and
latched into instruction register in Q4. It is decoded
and executed during the following Q1 through Q4. The
clocks and instruction execution flow is shown in
Figure 3-2 and Example 3-1.
3.2 Instruction Flo
w/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 fetched instruction is
latched into the Instruction Register (IR) 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
Q2 Q3 Q4
OSC1
Q1
Q2
Q3
Q4
PC
Q1
PC PC+1 PC+2
Fetch INST (PC)
Execute INST (PC-1) Fetch INST (PC+1)
Q1
EXAMPLE 3-1: INSTRUCTION PIPELINE FLOW
1. MOVLW 03H
2. MOVWF GPIO
3. CALL SUB_1
4. BSF GPIO, BIT1
Fetch 1 Execute 1
Fetch 2 Execute 2
Q2 Q3 Q4
Execute INST (PC) Fetch INST (PC+2)
Q2 Q3 Q4
Q1
Execute INST (PC+1)
Fetch 3 Execute 3
Fetch 4 Flush
Fetch SUB_1 Execute SUB_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.
DS40139D-page 12
1998 Microchip Technology Inc.
PIC12C5XX
4.0 MEMORY ORGANIZATION
PIC12C5XX memory is organized into program memory and data memory. For devices with more than 512
bytes of program memory, a paging scheme is used.
Program memory pages are accessed using one STATUS register bit. For the PIC12C509(A) with a data
memory register file of more than 32 registers, a banking scheme is used. Data memory banks are accessed
using the File Select Register (FSR).
4.1 Pr
The PIC12C5XX devices have a 12-bit Program
Counter (PC) capable of addressing a 2K x 12
program memory space.
Only the first 512 x 12 (0000h-01FFh) for the
PIC12C508(A) and 1K x 12 (0000h-03FFh) for the
PIC12C509(A) are physically implemented. Refer to
Figure 4-1. Accessing a location above these
boundaries will cause a wrap-around within the first
512 x 12 space (PIC12C508(A)) or 1K x 12 space
(PIC12C509(A)). The effective reset vector is at 000h,
(see Figure 4-1). Location 01FFh (PIC12C508(A)) or
location 03FFh (PIC12C509(A)) contains the internal
clock oscillator calibration value. This value should
never be overwritten.
ogram Memory Organization
FIGURE 4-1: PROGRAM MEMORY MAP
AND STACK FOR THE
PIC12C5XX
PC<11:0>
CALL, RETLW
Stack Level 1
Stack Level 2
Reset Vector (note 1)
On-chip Program
Memory
512 Word (PIC12C508(A))
Space
User Memory
On-chip Program
Memory
1024 Word (PIC12C509(A))
12
0000h
01FFh
0200h
03FFh
0400h
Note 1: Address 0000h becomes the
effective reset vector. Location
01FFh (PIC12C508(A)) or location
03FFh (PIC12C509(A)) contains
the MOVLW XX INTERNAL RC oscil-
lator calibration value.
7FFh
1998 Microchip Technology Inc. DS40139D-page 13
PIC12C5XX
4.2 Data Memor
y Organization
Data memory is composed of registers, or bytes of
RAM. Therefore, data memory for a device is specified
by its register file. The register file is divided into two
functional groups: special function registers and
general purpose registers.
The special function registers include the TMR0
register, the Program Counter (PC), the Status
Register, the I/O registers (ports), and the File Select
Register (FSR). In addition, special purpose registers
are used to control the I/O port configuration and
prescaler options.
The general purpose registers are used for data and
control information under command of the instructions.
For the PIC12C508(A), the register file is composed of
7 special function registers and 25 general purpose
registers (Figure 4-2).
For the PIC12C509(A), the register file is composed of
7 special function registers, 25 general purpose
registers, and 16 general purpose registers that may
be addressed using a banking scheme (Figure 4-3).
4.2.1 GENERAL PURPOSE REGISTER FILE The general purpose register file is accessed either
directly or indirectly through the file select register
FSR (Section 4.8).
FIGURE 4-2: PIC12C508(A) REGISTER FILE
MAP
File Address
(1)
00h
01h
02h
03h
04h
05h
06h
07h
1Fh
Note 1: Not a physical register. See Section 4.8
INDF
TMR0
PCL
STATUS
FSR
OSCCAL
GPIO
General
Purpose
Registers
FIGURE 4-3: PIC12C509(A) REGISTER FILE MAP
FSR<6:5> 00 01
File Address
00h
01h
02h
03h
04h
05h
06h
07h
0Fh
10h
1Fh
Note 1: Not a physical register. See Section 4.8
(1)
INDF
TMR0
PCL
STATUS
FSR
OSCCAL
GPIO
General
Purpose
Registers
General
Purpose
Registers
Bank 0 Bank 1
20h
Addresses map
back to
addresses
in Bank 0.
2Fh
30h
General
Purpose
Registers
3Fh
DS40139D-page 14
1998 Microchip Technology Inc.
PIC12C5XX
4.2.2 SPECIAL FUNCTION REGISTERS
The special registers can be classified into two sets.
The special function registers associated with the
The Special Function Registers (SFRs) are registers
used by the CPU and peripheral functions to control
the operation of the device (Table 4-1).
“core” functions are described in this section. Those
related to the operation of the peripheral features are
described in the section for each peripheral feature.
TABLE 4-1: SPECIAL FUNCTION REGISTER (SFR) SUMMARY
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
N/A TRIS I/O control registers
N/A OPTION
00h INDF Uses contents of FSR to address data memory (not a physical register)
01h TMR0 8-bit real-time clock/counter
(1)
02h
03h STATUS GPWUF — PA0 TO PD Z DC C
PCL Low order 8 bits of PC
Contains control bits to configure Timer0, Timer0/WDT
prescaler, wake-up on change, and weak pull-ups
Value on
Power-On
Reset
--11 1111 --11 1111
1111 1111 1111 1111
xxxx xxxx uuuu uuuu
xxxx xxxx uuuu uuuu
1111 1111 1111 1111
0001 1xxx q00q quuu
Value on
All Other
(2)
Resets
(3)
1998 Microchip Technology Inc. DS40139D-page 15
PIC12C5XX
4.3 STATUS Register
For example, CLRF STATUS will clear the upper three
bits and set the Z bit. This leaves the STATUS register
This register contains the arithmetic status of the ALU,
the RESET status, and the page preselect bit for
program memories larger than 512 words.
The STATUS register can be the destination for any
instruction, as with any other register. If 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
as 000u u1uu (where u = unchanged).
It is recommended, therefore, that only BCF, BSF and
MOVWF instructions be used to alter the STATUS
register because these instructions do not affect the Z,
DC or C bits from the STATUS register. For other
instructions, which do affect STATUS bits, see
Instruction Set Summary.
disabled. These bits are set or cleared according to
the 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.
FIGURE 4-4: STATUS REGISTER (ADDRESS:03h)
R/W-0 R/W-0 R/W-0 R-1 R-1 R/W-x R/W-x R/W-x
GPWUF
bit7 6 5 4 3 2 1 bit0
bit 7: GPWUF: GPIO reset bit
bit 6: Unimplemented
bit 5: PA0: Program page preselect bits
bit 4: TO: Time-out bit
bit 3: PD: Power-down bit
bit 2: Z: Zero bit
bit 1: DC: Digit carry/borrow bit (for ADDWF and SUBWF instructions)
bit 0: C: Carry/borrow bit (for ADDWF, SUBWF and RRF, RLF instructions)
—
1 = Reset due to wake-up from SLEEP on pin change
0 = After power up or other reset
1 = Page 1 (200h - 3FFh) - PIC12C509(A)
0 = Page 0 (000h - 1FFh) - PIC12C508(A) and PIC12C509(A)
Each page is 512 bytes.
Using the PA0 bit as a general purpose read/write bit in devices which do not use it for program
page preselect is not recommended since this may affect upward compatibility with future products.
1 = After power-up, CLRWDT instruction, or SLEEP instruction
0 = A WDT time-out occurred
1 = After power-up or by the CLRWDT instruction
0 = By execution of the SLEEP instruction
1 = The result of an arithmetic or logic operation is zero
0 = The result of an arithmetic or logic operation is not zero
ADDWF
1 = A carry from the 4th low order bit of the result occurred
0 = A carry from the 4th low order bit of the result did not occur
SUBWF
1 = A borrow from the 4th low order bit of the result did not occur
0 = A borrow from the 4th low order bit of the result occurred
ADDWF SUBWF RRF or RLF
1 = A carry occurred 1 = A borrow did not occur Load bit with LSB or MSB, respectively
0 = A carry did not occur 0 = A borrow occurred
PA0 TO PD Z DC C R = Readable bit
W = Writable bit
- n = Value at POR reset
DS40139D-page 16 1998 Microchip Technology Inc.
PIC12C5XX
4.4 OPTION Register
The OPTION register is a 8-bit wide, write-only
register which contains various control bits to
configure the Timer0/WDT prescaler and Timer0.
By executing the OPTION instruction, the contents of
the W register will be transferred to the OPTION
Note: If TRIS bit is set to ‘0’, the wake-up on
change and pull-up functions are disabled
for that pin; i.e., note that TRIS overrides
OPTION control of GPPU
Note: If the T0CS bit is set to ‘1’, GP2 is f orced to
be an input even if TRIS GP2 = ‘0’.
register. A RESET sets the OPTION<7:0> bits.
FIGURE 4-5: OPTION REGISTER
W-1 W-1 W-1 W-1 W-1 W-1 W-1 W-1
GPWU GPPU T0CS T0SE PSA PS2 PS1 PS0 W = Writable bit
bit7 6 5 4 3 2 1 bit0
bit 7: GPWU
bit 6: GPPU: Enable weak pull-ups (GP0, GP1, GP3)
bit 5: T0CS: Timer0 clock source select bit
bit 4: T0SE: Timer0 source edge select bit
bit 3: PSA: Prescaler assignment bit
bit 2-0: PS2:PS0: Prescaler rate select bits
: Enable wake-up on pin change (GP0, GP1, GP3)
1 = Disabled
0 = Enabled
1 = Disabled
0 = Enabled
1 = Transition on T0CKI pin
0 = Transition on internal instruction cycle clock, Fosc/4
1 = Increment on high to low transition on the T0CKI pin
0 = Increment on low to high transition on the T0CKI pin
1 = Prescaler assigned to the WDT
0 = Prescaler assigned to Timer0
Bit Value Timer0 Rate WDT Rate
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
U = Unimplemented bit
- n = Value at POR reset
Reference Table 4-1 for
other resets.
and GPWU.
1998 Microchip Technology Inc. DS40139D-page 17
PIC12C5XX
4.5 OSCCAL Register
The Oscillator Calibration (OSCCAL) register is used to
calibrate the internal 4 MHz oscillator. It contains f our to
six bits for calibration. Increasing the cal value
increases the frequency. See Section 7.2.5 for more
information on the internal oscillator.
FIGURE 4-6: OSCCAL REGISTER (ADDRESS 8Fh)
R/W-0 R/W-1 R/W-1 R/W-1 R/W-0 R/W-0 U-0 U-0
CAL3 CAL2 CAL1 CAL0 — — — — R = Readable bit
bit7 bit0
bit 7-4: CAL<3:0>: Calibration
bit 3-0: Unimplemented: Read as '0'
FIGURE 4-7: OSCCAL REGISTER (ADDRESS 8Fh)PIC12C508A/C509A
W = Writable bit
U = Unimplemented bit,
read as ‘0’
- n = Value at POR reset
R/W-1 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 U-0 U-0
CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 — — R = Readable bit
bit7 bit0
bit 7-2: CAL<5:0>: Calibration
bit 1-0: Unimplemented: Read as '0'
W = Writable bit
U = Unimplemented bit,
read as ‘0’
- n = Value at POR reset
DS40139D-page 18 1998 Microchip Technology Inc.
PIC12C5XX
4.6 Program Counter
As a program instruction is executed, the Program
Counter (PC) will contain the address of the next
program instruction to be executed. The PC value is
increased by one every instruction cycle, unless an
instruction changes the PC.
For a GOTO instruction, bits 8:0 of the PC are provided
by the GOTO instruction word. The PC Latch (PCL) is
mapped to PC<7:0>. Bit 5 of the STATUS register
provides page information to bit 9 of the PC (Figure 4-
8).
For a CALL instruction, or any instruction where the
PCL is the destination, bits 7:0 of the PC again are
provided by the instruction word. However, PC<8>
does not come from the instruction word, but is always
cleared (Figure 4-8).
Instructions where the PCL is the destination, or
Modify PCL instructions, include MOVWF PC, ADDWF
PC, and BSF PC,5.
Note: Because PC<8> is cleared in the CALL
instruction, or any Modify PCL instruction,
all subroutine calls or computed jumps are
limited to the first 256 locations of any program memory page (512 words long).
FIGURE 4-8: LOADING OF PC
BRANCH INSTRUCTIONS -
PIC12C5XX
GOTO Instruction
11
PC
7 0
CALL or Modify PCL Instruction
11
PC
8 7 0
910
PCL
Instruction Word
PA0
STATUS
8 7 0
910
PCL
4.6.1 EFFECTS OF RESET The Program Counter is set upon a RESET, which
means that the PC addresses the last location in the
last page i.e., the oscillator calibration instruction. After
executing MOVLW XX, the PC will roll over to location
00h, and begin executing user code.
The STATUS register page preselect bits are cleared
upon a RESET, which means that page 0 is preselected.
Therefore, upon a RESET, a GOTO instruction will
automatically cause the program to jump to page 0
until the value of the page bits is altered.
4.7 Stack
PIC12C5XX devices have a 12-bit wide L.I.F.O.
hardware push/pop stack.
push
A CALL instruction will
1 into stack 2 and then push the current program
counter value, incremented by one , into stac k le vel 1. If
more than two sequential CALL’s are executed, only
the most recent two return addresses are stored.
A RETLW instruction will
1 into the program counter and then copy stack level 2
contents into level 1. If more than two sequential
RETLW’s are executed, the stack will be filled with the
address previously stored in level 2. Note that the
W register will be loaded with the literal value specified
in the instruction. This is particularly useful for the
implementation of data look-up tables within the
program memory.
Upon any reset, the contents of the stack remain
unchanged, however the program counter (PCL) will
also be reset to 0.
Note 1: There are no STATUS bits to indicate
stack overflows or stack underflow conditions.
Note 2: There are no instructions mnemonics
called PUSH or POP. These are actions
that occur from the execution of the CALL
and RETLW instructions.
the current value of stack
pop
the contents of stack level
Instruction Word
Reset to ‘0’
PA0
7 0
STATUS
1998 Microchip Technology Inc. DS40139D-page 19
PIC12C5XX
4.8 Indirect Data 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 07 contains the value 10h
• Register file 08 contains the value 0Ah
• Load the value 07 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 = 08)
• A read of the INDR 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 10h-1Fh
using indirect addressing is shown in Example 4-2.
EXAMPLE 4-2: HOW TO CLEAR RAM
USING INDIRECT
ADDRESSING
movlw 0x10 ;initialize pointer
movwf FSR ; to RAM
NEXT clrf INDF ;clear INDF register
incf FSR,F ;inc pointer
btfsc FSR,4 ;all done?
goto NEXT ;NO, clear next
CONTINUE
: ;YES, continue
The FSR is a 5-bit wide register. It is used in
conjunction with the INDF register to indirectly address
the data memory area.
The FSR<4:0> bits are used to select data memory
addresses 00h to 1Fh.
PIC12C508(A): Does not use banking. FSR<7:5> are
unimplemented and read as '1's.
PIC12C509(A): Uses FSR<5>. Selects between bank
0 and bank 1. FSR<7:6> is unimplemented, read as '1’
.
FIGURE 4-9: DIRECT/INDIRECT ADDRESSING
Direct Addressing
(FSR)
5
6
bank select
location select
(opcode) 04
00 01
00h
Data
Memory
0Fh
(1)
10h
1Fh 3Fh
Bank 0 Bank 1
Note 1: For register map detail see Section 4.2.
Note 2: PIC12C509(A) only
Addresses
map back to
addresses
in Bank 0.
(2)
Indirect Addressing
5
6
bank
(FSR)
4
location select
0
DS40139D-page 20 1998 Microchip Technology Inc.
PIC12C5XX
5.0 I/O PORT
As with any other register, the I/O register can be
written and read under program control. However,
read instructions (e.g., MOVF GPIO,W) always read the
I/O pins independent of the pin’s input/output modes.
On RESET, all I/O por ts are defined as input (inputs
are at hi-impedance) since the I/O control registers are
all set.
5.1 GPIO
GPIO is an 8-bit I/O register. Only the low order 6 bits
are used (GP5:GP0). Bits 7 and 6 are unimplemented
and read as '0's. Please note that GP3 is an input only
pin. The configuration word can set several I/O’s to
alternate functions. When acting as alternate functions
the pins will read as ‘0’ during port read. Pins GP0,
GP1, and GP3 can be configured with weak pull-ups
and also with wake-up on change. The wake-up on
change and weak pull-up functions are not pin
selectable. If pin 4 is configured as MCLR
up is always on and wake-up on change for this pin is
not enabled.
5.2 TRIS Register
The output driver control register is loaded with the
contents of the W register by executing the TRIS f
instruction. A '1' from a TRIS register bit puts the
corresponding output driver in a hi-impedance mode.
A '0' puts the contents of the output data latch on the
selected pins, enabling the output buffer. The
exceptions are GP3 which is input only and GP2 which
may be controlled by the option register, see Figure 4-
5.
, weak pull-
5.3 I/O Interfacing
The equivalent circuit for an I/O port pin is shown in
Figure 5-1. All port pins, except GP3 which is input
only, may be used for both input and output
operations. For input operations these ports are nonlatching. Any input must be present until read by an
input instruction (e.g., MOVF GPIO,W). The outputs are
latched and remain unchanged until the output latch is
rewritten. To use a port pin as output, the
corresponding direction control bit in TRIS must be
cleared (= 0). For use as an input, the corresponding
TRIS bit must be set. Any I/O pin (except GP3) can be
programmed individually as input or output.
FIGURE 5-1: EQUIVALENT CIRCUIT
FOR A SINGLE I/O PIN
Data
Bus
WR
Port
W
Reg
TRIS ‘f’
Data
Latch
CK
TRIS
Latch
CK
Reset
QD
VDD
Q
QD
Q
(2)
P
N
VSS
I/O
pin
(1)
Note: A read of the por ts reads the pins, not the
output data latches. That is, if an output
driver on a pin is enabled and driven high,
but the external system is holding it low, a
read of the port will indicate that the pin is
Note 1: I/O pins have protection diodes to VDD and VSS.
2: See Table 3-1 for buffer type.
RD Port
low.
The TRIS registers are “write-only” and are set (output
drivers disabled) upon RESET.
TABLE 5-1: SUMMARY OF PORT REGISTERS
Value on
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
N/A TRIS I/O control registers --11 1111 --11 1111
N/A
03H
06h
Legend: Shaded cells not used by Port Registers, read as ‘0’, — = unimplemented, read as '0', x = unknown, u = unchanged,
Note 1: If reset was due to wake-up on change, then bit 7 = 1. All other resets will cause bit 7 = 0.
OPTION GPWU GPPU T0CS T0SE PSA PS2 PS1 PS0
STATUS
GPIO
q = see tables in Section 7.7 for possible values.
GPWUF — PAO TO PD Z DC C 0001 1xxx q00q quuu
— — GP5 GP4 GP3 GP2 GP1 GP0 --xx xxxx --uu uuuu
Power-On
Reset
1111 1111 1111 1111
Value on
All Other Resets
(1)
1998 Microchip Technology Inc. DS40139D-page 21
PIC12C5XX
5.4 I/O Programming Considerations
5.4.1 BI-DIRECTIONAL I/O PORTS
Some instructions operate internally as read followed
by write operations. The BCF and BSF instructions, for
example, read the entire port into the CPU, execute
the bit operation and re-write the result. Caution must
be used when these instructions are applied to a port
where one or more pins are used as input/outputs. For
example, a BSF operation on bit5 of GPIO will cause all
eight bits of GPIO to be read into the CPU, bit5 to be
set and the GPIO value to be written to the output
latches. If another bit of GPIO is used as a bidirectional I/O pin (say 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
may now be unknown.
Example 5-1 shows the effect of two sequential readmodify-write instructions (e.g., BCF, BSF , etc.) on an I/
O port.
A pin actively outputting a high or a low 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 currents may damage the
chip.
EXAMPLE 5-1: READ-MODIFY-WRITE
INSTRUCTIONS ON AN
I/O PORT
;Initial GPIO Settings
; GPIO<5:3> Inputs
; GPIO<2:0> Outputs
;
; GPIO latch GPIO pins
; ---------- --------- BCF GPIO, 5 ;--01 -ppp --11 pppp
BCF GPIO, 4 ;--10 -ppp --11 pppp
MOVLW 007h ;
TRIS GPIO ;--10 -ppp --11 pppp
;
;Note that the user may have expected the pin
;values to be --00 pppp. The 2nd BCF caused
;GP5 to be latched as the pin value (High).
5.4.2 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 5-2). Therefore, care must be exercised if a
write followed by a read operation is carried out on the
same I/O port. The sequence of instructions should
allow the pin voltage to stabilize (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.
FIGURE 5-2: SUCCESSIVE I/O OPERATION
NOP
Q3
Q4
Instruction
fetched
GP5:GP0
Instruction
executed
Q4
Q1 Q2
MOVWF GPIO
Q3
PC PC + 1 PC + 2
Q1 Q2
MOVF GPIO,W
Port pin
written here
MOVWF GPIO
(Write to
GPIO)
Q3
Q4
Q1 Q2
Port pin
sampled here
MOVF GPIO,W
(Read
GPIO)
Q1 Q2
Q3
PC + 3
NOP
NOP
Q4
This example shows a write to GPIO follow ed
by a read from GPIO.
Data setup time = (0.25 TCY – TPD)
where: TCY = instruction cycle.
TPD = propagation delay
Therefore, at higher clock frequencies, a
write followed by a read may be problematic.
DS40139D-page 22 1998 Microchip Technology Inc.
PIC12C5XX
6.0 TIMER0 MODULE AND TMR0 REGISTER
The Timer0 module has the following features:
• 8-bit timer/counter register, TMR0
- Readable and writable
• 8-bit software programmable prescaler
• Internal or external clock select
- Edge select for external clock
Figure 6-1 is a simplified block diagram of the Timer0
module.
Timer mode is selected by clearing the T0CS bit
(OPTION<5>). In timer mode, the Timer0 module will
increment every instruction cycle (without prescaler). If
TMR0 register is written, the increment is inhibited for
the following two instruction cycles (Figure 6-2 and
Figure 6-3). The user can work around this by writing
an adjusted value to the TMR0 register.
FIGURE 6-1: TIMER0 BLOCK DIAGRAM
GP2/T0CKI
Pin
T0SE
FOSC/4
0
1
T0CS
PS2, PS1, PS0
(1)
Programmable
Prescaler
Counter mode is selected by setting the T0CS bit
(OPTION<5>). In this mode, Timer0 will increment
either on every rising or falling edge of pin T0CKI. The
T0SE bit (OPTION<4>) determines the source edge.
Clearing the T0SE bit selects the rising edge.
Restrictions on the external clock input are discussed
in detail in Section 6.1.
The prescaler may be used by either the Timer0
module or the Watchdog Timer, but not both. The
prescaler assignment is controlled in software by the
control bit PSA (OPTION<3>). Clearing the PSA bit
will assign the prescaler to Timer0. The prescaler is
not readable or writable. When the prescaler is
assigned to the Timer0 module, prescale v alues of 1:2,
1:4,..., 1:256 are selectable. Section 6.2 details the
operation of the prescaler.
A summary of registers associated with the Timer0
module is found in Table 6-1.
Data bus
PSout
1
(2)
3
0
PSA
(1)
(1)
Sync with
Internal
Clocks
CY delay)
(2 T
TMR0 reg
PSout
Sync
8
Note 1: Bits T0CS, T0SE, PSA, PS2, PS1 and PS0 are located in the OPTION register.
2: The prescaler is shared with the Watchdog Timer (Figure 6-5).
1998 Microchip Technology Inc. DS40139D-page 23
PIC12C5XX
FIGURE 6-2: TIMER0 TIMING: INTERNAL CLOCK/NO PRESCALE
PC
(Program
Counter)
Instruction
Fetch
Timer0
Instruction
Executed
Q1 Q2 Q3 Q4
PC-1
T0
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 PC+1 PC+2 PC+3 PC+4 PC+5 PC+6
MOVWF TMR0
T0+1 T0+2 NT0 NT0+1 NT0+2
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
FIGURE 6-3: TIMER0 TIMING: INTERNAL CLOCK/PRESCALE 1:2
PC
(Program
Counter)
Instruction
Fetch
Timer0
Instruction
Execute
Q1 Q2 Q3 Q4
PC-1
T0 NT0+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
PC PC+1 PC+2 PC+3 PC+4 PC+5 PC+6
MOVWF TMR0
T0+1
MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W
NT0
Write TMR0
executed
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0 + 1
TABLE 6-1: REGISTERS ASSOCIATED WITH TIMER0
Value on
Power-On
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Reset
01h TMR0 Timer0 - 8-bit real-time clock/counter xxxx xxxx uuuu uuuu
N/A OPTION
N/A TRIS
Legend: Shaded cells not used by Timer0,
GPWU GPPU T0CS T0SE PSA PS2 PS1 PS0 1111 1111 1111 1111
—
— GP5 GP4 GP3 GP2 GP1 GP0
- = unimplemented, x = unknown, u = unchanged,
--11 1111 --11 1111
Value on
All Other
Resets
T0
DS40139D-page 24 1998 Microchip Technology Inc.
PIC12C5XX
6.1 Using Timer0 with an External Clock
When an external clock input is used for Timer0, it
must meet certain requirements. The external clock
requirement is due to internal phase clock (T
synchronization. Also, there is a delay in the actual
incrementing of Timer0 after synchronization.
6.1.1 EXTERNAL CLOCK SYNCHRONIZATION
When no prescaler is used, the external clock input is
the same as the prescaler output. The synchronization
of 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 6-4). Therefore, it is necessary for T0CKI to be
high for at least 2T
and low for at least 2T
OSC (and a small RC delay of 20 ns)
OSC (and a small RC delay of
20 ns). Refer to the electrical specification of the
desired device.
OSC)
When a prescaler is used, the external clock input is
divided by the 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 (and a small RC delay of
40 ns) 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
electrical specification of the desired device.
6.1.2 TIMER0 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 6-4 shows the
delay from the external clock edge to the timer
incrementing.
6.1.3 OPTION REGISTER EFFECT ON GP2 TRIS If the option register is set to read TIMER0 from the pin,
the port is forced to an input regardless of the TRIS register setting.
FIGURE 6-4: TIMER0 TIMING WITH EXTERNAL CLOCK
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
External Clock Input or
Prescaler Output (2)
External Clock/Prescaler
Output After Sampling
Increment Timer0 (Q4)
Note 1:
Delay from clock input change to Timer0 increment is 3Tosc to 7Tosc. (Duration of Q = Tosc).
Therefore, the error in measuring the interval between two edges on Timer0 input = ± 4Tosc max.
2:
External clock if no prescaler selected, Prescaler output otherwise.
3:
The arrows indicate the points in time where sampling occurs.
(3)
Timer0
(1)
T0 T0 + 1 T0 + 2
Small pulse
misses sampling
1998 Microchip Technology Inc. DS40139D-page 25
PIC12C5XX
6.2 Prescaler
An 8-bit counter is available as a prescaler for the
Timer0 module, or as a postscaler for the Watchdog
Timer (WDT), respectively (Section 7.6). For simplicity,
this counter is being referred to as “prescaler”
throughout this data sheet. Note that the prescaler
may be used by either the Timer0 module or the WDT,
but not both. Thus, a prescaler assignment for the
Timer0 module means that there is no prescaler for
the WDT, and vice-versa.
The PSA and PS2:PS0 bits (OPTION<3:0>)
determine prescaler assignment and prescale ratio.
When assigned to the Timer0 module, all instructions
writing to the TMR0 register (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 WDT. The prescaler is neither readable
nor writable. On a RESET, the prescaler contains all
'0's.
6.2.1 SWITCHING PRESCALER ASSIGNMENT The prescaler assignment is fully under software control
(i.e., it can be changed “on the fly” during program
execution). 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.
EXAMPLE 6-1: CHANGING PRESCALER
(TIMER0→WDT)
1.CLRWDT ;Clear WDT
2.CLRF TMR0 ;Clear TMR0 & Prescaler
3.MOVLW '00xx1111’b ;These 3 lines (5, 6, 7)
4.OPTION ; are required only if
; desired
5.CLRWDT ;PS<2:0> are 000 or 001
6.MOVLW '00xx1xxx’b ;Set Postscaler to
7.OPTION ; desired WDT rate
To change prescaler from the WDT to the Timer0
module, use the sequence shown in Example 6-2. This
sequence must be used even if the WDT is disabled. A
CLRWDT instruction should be executed bef ore switching
the prescaler.
EXAMPLE 6-2: CHANGING PRESCALER
(WDT→TIMER0)
CLRWDT ;Clear WDT and
;prescaler
MOVLW 'xxxx0xxx' ;Select TMR0, new
;prescale value and
;clock source
OPTION
FIGURE 6-5: BLOCK DIAGRAM OF THE TIMER0/WDT PRESCALER
TCY ( = Fosc/4)
M
U
X
PSA
0
1
T0CS
M
U
X
1
0
8-bit Prescaler
8
8 - to - 1MUX
0
1
MUX
M
U
X
PSA
PSA
Sync
2
Cycles
PS2:PS0
GP2/T0CKI
Pin
T0SE
Watchdog
Timer
WDT Enable bit
0
1
Data Bus
8
TMR0 reg
WDT
Time-Out
Note: T0CS, T0SE, PSA, PS2:PS0 are bits in the OPTION register.
DS40139D-page 26 1998 Microchip Technology Inc.
PIC12C5XX
7.0 SPECIAL FEATURES OF THE CPU
What sets a microcontroller apart from other
processors are special circuits to deal with the needs
of real-time applications. The PIC12C5XX family of
microcontrollers has a host of such features intended
to maximize system reliability, minimize cost through
elimination of external components, provide power
saving operating modes and offer code protection.
These features are:
• Oscillator selection
• Reset
- Power-On Reset (POR)
- Device Reset Timer (DRT)
- Wake-up from SLEEP on pin change
• Watchdog Timer (WDT)
• SLEEP
• Code protection
• ID locations
• In-circuit Serial Programming
The PIC12C5XX has a Watchdog Timer which can be
shut off only through configuration bit WDTE. It r uns
off of its own RC oscillator for added reliability. If using
XT or LP selectable oscillator options, there is always
an 18 ms (nominal) delay provided by the Device
Reset Timer (DRT), intended to keep the chip in reset
until the crystal oscillator is stable. If using INTRC or
EXTRC there is an 18 ms delay only on V
DD power-up.
With this timer on-chip, most applications need no
external reset circuitry.
The SLEEP mode is designed to offer a very low
current power-down mode. The user can wake-up
from SLEEP through a change on input pins or
through a Watchdog Timer time-out. Several oscillator
options are also made available to allow the part to fit
the application, including an internal 4 MHz oscillator.
The EXTRC oscillator option saves system cost while
the LP crystal option saves power. A set of
configuration bits are used to select various options.
7.1 Configuration Bits
The PIC12C5XX configuration word consists of 12
bits. Configuration bits can be programmed to select
various device configurations. Two bits are for the
selection of the oscillator type, one bit is the Watchdog
Timer enable bit, and one bit is the MCLR
enable bit.
FIGURE 7-1: CONFIGURATION WORD FOR PIC12C5XX
— — — — — — — MCLRE CP WDTE FOSC1 FOSC0 Register: CONFIG
bit11 10 9 8 7 6 5 4 3 2 1 bit0
bit 11-5: Unimplemented
bit 4: MCLRE: MCLR
1 = MCLR pin enabled
0 = MCLR tied to VDD, (Internally)
bit 3: CP: Code protection bit.
1 = Code protection off
0 = Code protection on
bit 2: WDTE: Watchdog timer enable bit
1 = WDT enabled
0 = WDT disabled
bit 1-0: FOSC1:FOSC0: Oscillator selection bits
11 = EXTRC - external RC oscillator
10 = INTRC - internal RC oscillator
01 = XT oscillator
00 = LP oscillator
Note 1: Refer to the PIC12C5XX Programming Specifications to determine how to access the
configuration word. This register is not user addressable during device operation.
enable bit.
Address
(1)
: FFFh
1998 Microchip Technology Inc. DS40139D-page 27
PIC12C5XX
7.2 Oscillator Configurations
7.2.1 OSCILLATOR TYPES The PIC12C5XX can be operated in four different
oscillator modes. The user can program two
configuration bits (FOSC1:FOSC0) to select one of
these four modes:
• LP: Low Power Crystal
• XT: Crystal/Resonator
• INTRC: Internal 4 MHz Oscillator
• EXTRC: External Resistor/Capacitor
7.2.2 CRYSTAL OSCILLATOR / CERAMIC
RESONATORS
In XT or LP modes, a crystal or ceramic resonator is
connected to the GP5/OSC1/CLKIN and GP4/OSC2
pins to establish oscillation (Figure 7-2). The
PIC12C5XX oscillator design requires the use of a
parallel cut crystal. Use of a series cut crystal may
give a frequency out of the crystal manufacturers
specifications. When in XT or LP modes, the device
can have an external clock source drive the GP5/
OSC1/CLKIN pin (Figure 7-3).
FIGURE 7-2: CRYSTAL OPERATION (OR
CERAMIC RESONATOR) (XT
OR LP OSC
CONFIGURATION)
(1)
C1
OSC1
PIC12C5XX
TABLE 7-1: CAPACITOR SELECTION
FOR CERAMIC RESONATORS
- PIC12C5XX
Osc
Type
These values are for design guidance only. Since
each resonator has its own characteristics, the user
should consult the resonator manufacturer for
appropriate values of external components.
Resonator
Freq
XT 4.0 MHz 30 pF 30 pF
Cap. RangeC1Cap. Range
C2
T ABLE 7-2: CAPACITOR SELECTION
FOR CRYSTAL OSCILLATOR
- PIC12C5XX
Osc
Type
Note 1: For V
These values are for design guidance only. Rs may
be required to avoid overdriving crystals with low
drive level specification. Since each crystal has its
own characteristics, the user should consult the crystal manufacturer for appropriate values of external
components.
Resonator
Freq
LP 32 kHz
XT 200 kHz
1 MHz
4 MHz
DD > 4.5V, C1 = C2 ≈ 30 pF is
recommended.
(1)
Cap.Range
C1
15 pF 15 pF
47-68 pF
15 pF
15 pF
Cap. Range
C2
47-68 pF
15 pF
15 pF
XTAL
OSC2
(2)
RS
(1)
C2
Note 1: See Capacitor Selection tables for
recommended values of C1 and C2.
2: A series resistor (RS) may be required for
AT strip cut crystals.
3: RF approximate value = 10 MΩ.
RF
(3)
SLEEP
To internal
logic
FIGURE 7-3: EXTERNAL CLOCK INPUT
OPERATION (XT OR LP OSC
CONFIGURATION)
Clock from
ext. system
Open
OSC1
PIC12C5XX
OSC2
DS40139D-page 28 1998 Microchip Technology Inc.
PIC12C5XX
7.2.3 EXTERNAL CRYSTAL OSCILLATOR CIRCUIT
Either a prepackaged oscillator or a simple oscillator
circuit with TTL gates can be used as an external
crystal oscillator circuit. Prepackaged oscillators
provide a wide operating range and better stability. A
well-designed crystal oscillator will provide good
performance with TTL gates. Two types of crystal
oscillator circuits can be used: one with parallel
resonance, or one with series resonance.
Figure 7-4 shows implementation of a parallel
resonant oscillator circuit. The circuit is designed to
use the fundamental frequency of the crystal. The
74AS04 inverter performs the 180-degree phase shift
that a parallel oscillator requires. The 4.7 kΩ resistor
provides the negative feedback for stability. The 10 kΩ
potentiometers bias the 74AS04 in the linear region.
This circuit could be used for external oscillator
designs.
FIGURE 7-4: EXTERNAL PARALLEL
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
+5V
10k
4.7k
74AS04
10k
XTAL
10k
20 pF
20 pF
Figure 7-5 shows a series resonant oscillator circuit.
This circuit is also designed to use the fundamental
frequency of the crystal. The inverter performs a 180degree phase shift in a series resonant oscillator
circuit. The 330 Ω resistors provide the negative
feedback to bias the inverters in their linear region.
74AS04
To Other
Devices
PIC12C5XX
CLKIN
FIGURE 7-5: EXTERNAL SERIES
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
To Other
74AS04
Devices
PIC12C5XX
CLKIN
330
74AS04
330
74AS04
0.1 µF
XTAL
7.2.4 EXTERNAL RC OSCILLATOR For timing insensitive applications, the RC device
option offers additional cost savings. The RC oscillator
frequency is a function of the supply voltage, the
resistor (Rext) and capacitor (Cext) values, and the
operating temperature. In addition to this, the oscillator
frequency will vary from unit to unit due to normal
process parameter variation. Furthermore, the
difference in lead frame capacitance between package
types will also affect the oscillation frequency,
especially for low Cext values. The user also needs to
take into account variation due to tolerance of external
R and C components used.
Figure 7-6 shows how the R/C combination is
connected to the PIC12C5XX. For Rext values below
2.2 kΩ, the oscillator operation may become unstable,
or stop completely. For very high Rext values
(e.g., 1 MΩ) the oscillator becomes sensitive to noise,
humidity and leakage. Thus, we recommend keeping
Rext between 3 kΩ and 100 kΩ.
Although the oscillator will operate with no external
capacitor (Cext = 0 pF), we recommend using values
above 20 pF for noise and stability reasons. With no or
small external capacitance, the oscillation frequency
can vary dramatically due to changes in external
capacitances, such as PCB trace capacitance or
package lead frame capacitance.
The Electrical Specifications sections show RC
frequency variation from part to part due to normal
process variation. The variation is larger for larger R
(since leakage current variation will affect RC
frequency more for large R) and for smaller C (since
variation of input capacitance will affect RC frequency
more).
Also, see the Electrical Specifications sections for
variation of oscillator frequency due to V
DD for given
Rext/Cext values as well as frequency variation due to
operating temperature for giv en R, C, and V
DD values.
FIGURE 7-6: EXTERNAL RC OSCILLATOR
MODE
VDD
Rext
Cext
SS
V
OSC1
N
Internal
clock
PIC12C5XX
1998 Microchip Technology Inc. DS40139D-page 29
PIC12C5XX
7.2.5 INTERNAL 4 MHz RC OSCILLATOR The internal RC oscillator provides a fixed 4 MHz (nom-
inal) system clock at VDD = 5V and 25°C, see “Electri-
cal Specifications” section for infor mation on variation
over voltage and temperature..
In addition, a calibration instruction is programmed into
the top of memory which contains the calibration value
for the internal RC oscillator. This location is ne ver code
protected regardless of the code protect settings. This
value is programmed as a MOVLW XX instruction where
XX is the calibration value, and is placed at the reset
vector. This will load the W register with the calibration
value upon reset and the PC will then roll over to the
users program at address 0x000. The user then has the
option of writing the value to the OSCCAL Register
(05h) or ignoring it.
OSCCAL, when written to with the calibration value, will
“trim” the internal oscillator to remove process variation
from the oscillator frequency. .
Note: Please note that erasing the device will
also erase the pre-programmed internal
calibration value for the internal oscillator.
The calibration value must be read prior to
erasing the part. so it can be reprogrammed correctly later.
For the PIC12C508A and PIC12C509A, bits <7:2>,
CAL5-CAL0 are used for calibration. Adjusting CAL50 from 000000 to 111111 yields a higher clock speed.
Note that bits 1 and 0 of OSCCAL are unimplemented
and should be written as 0 when modifying OSCCAL
for compatibility with future devices.
For the PIC12C508 and PIC12C509, the lower 4 bits of
the register are used. Writing a larger value in this location yields a higher clock speed.
are TO, PD, and GPWUF bits. They are set or cleared
differently in different reset situations. These bits are
used in software to determine the nature of reset. See
Table 7-3 for a full description of reset states of all
registers.
7.3 RESET
The device differentiates between various kinds of
reset:
a) Power on reset (POR)
b) MCLR
c) MCLR
d) WDT time-out reset during normal operation
e) WDT time-out reset during SLEEP
f) Wake-up from SLEEP on pin change
Some registers are not reset in any way; they are
unknown on POR and unchanged in any other reset.
Most other registers are reset to “reset state” on po weron reset (POR), MCLR
change reset during normal operation. They are not
affected by a WDT reset during SLEEP or MCLR
during SLEEP, since these resets are viewed as
resumption of normal operation. The exceptions to this
DS40139D-page 30 1998 Microchip Technology Inc.
reset during normal operation
reset during SLEEP
, WDT or wake-up on pin
reset
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