PIC16C63A Microchip Technology, PIC16C63A Datasheet - Page 23

• Manufacturer Part Number: PIC16C63A
• Description: 28/40-Pin 8-Bit CMOS Microcontrollers
• Manufacturer: Microchip Technology

2.3
The program counter (PC) specifies the address of the
instruction to fetch for execution. The PC is 13 bits
wide. The low byte is called the PCL register. This reg-
ister is readable and writable. The high byte is called
the PCH register. This register contains the PC<12:8>
bits and is not directly readable or writable. All updates
to the PCH register go through the PCLATH register.
2.3.1
The stack allows a combination of up to 8 program calls
and interrupts to occur. The stack contains the return
address from this branch in program execution.
Mid-Range devices have 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 interrupt
causes a branch. The stack is POPed in the event of a
RETURN, RETLW or a RETFIE instruction execution.
PCLATH is not modified when the stack is PUSHed or
POPed.
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).
1998 Microchip Technology Inc.
STACK
PCL and PCLATH
PIC16C63A/65B/73B/74B
2.4
The CALL and GOTO instructions provide 11 bits of
address to allow branching within any 2K program
memory page. When doing a CALL or GOTO instruction
the upper bit of the address is provided by
PCLATH<3>. When doing a CALL or GOTO instruction,
the user must ensure that the page select bit is pro-
grammed so that the desired program memory page is
addressed. If a return from a CALL instruction (or inter-
rupt) is executed, the entire 13-bit PC is pushed onto
the stack. Therefore, manipulation of the PCLATH<3>
bit is not required for the return instructions (which
POPs the address from the stack).
Program Memory Paging
DS30605A-page 23