PIC16LC712 datasheet(19/106 Pages) MICROCHIP

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DS41106C-page 19

PIC16C712/716

2.3

PCL and PCLATH

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

STACK

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).

2.4

Program Memory Paging

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

the

address

provided

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).

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