PIC12CE67 Microchip Technology, PIC12CE67 Datasheet - Page 22

• Manufacturer Part Number: PIC12CE67
• Description: 8-Pin/ 8-Bit CMOS Microcontroller with A/D Converter and EEPROM Data Memory
• Manufacturer: Microchip Technology

PIC12CE67X
4.3
The program counter (PC) is 13-bits wide. The low byte
comes from the PCL register, which is a readable and
writable register. The high byte (PC<12:8>) is not
directly readable or writable and comes from PCLATH.
On any reset, the PC is cleared. Figure 4-10 shows the
two situations for the loading of the PC. The upper
example in the figure shows how the PC is loaded on a
write to PCL (PCLATH<4:0>
ple in the figure shows how the PC is loaded during a
CALL or GOTO instruction (PCLATH<4:3>
FIGURE 4-10: LOADING OF PC IN
4.3.1
A computed GOTO is accomplished by adding an off-
set 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 byte block). Refer to the
application note “Implementing a Table Read" (AN556).
DS40181B-page 22
PC
PC
12
12 11 10
2
PCL and PCLATH
COMPUTED GOTO
PCH
5
PCLATH<4:3>
PCH
PCLATH
PCLATH<4:0>
8
PCLATH
8
DIFFERENT SITUATIONS
7
7
PCL
PCL
PCH). The lower exam-
11
8
0
0
Instruction with
PCL as
Destination
ALU result
GOTO, CALL
Opcode <10:0>
PCH).
Preliminary
4.3.2
The PIC12C67X family has an 8 level deep x 13-bit
wide hardware stack. The stack space is not part of
either program or data space and the stack pointer is
not readable or writable. The PC is PUSHed onto the
stack when a CALL instruction is executed or an inter-
rupt causes a branch. The stack is POPed in the event
of a RETURN, RETLW or a RETFIE instruction execution.
PCLATH is not affected by a PUSH or POP operation.
The stack operates as a circular buffer. This means that
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).
4.4
The
PCLATH<4:3>, which are used to access program
memory when more than one page is available. The
use of PCLATH<4:3> as general purpose read/write
bits for the PIC12CE67X is not recommended since
this may affect upward compatibility with future prod-
ucts.
Note 1: There are no status bits to indicate stack
Note 2: There are no instructions/mnemonics
PIC12CE67X
STACK
Program Memory Paging
overflow or stack underflow conditions.
called PUSH or POP. These are actions
that occur from the execution of the CALL,
RETURN,
tions, or the vectoring to an interrupt
address.
ignores
RETLW, and RETFIE instruc-
1998 Microchip Technology Inc.
both
paging
bits