PIC16LC774-04SLASHSS datasheet(24/200 Pages) MICROCHIP

24 / 200 page

PIC16C77X

DS30275A-page 24

Advance Information

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.

Midrange 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

PIC16C77X devices are capable of addressing a con-

tinuous 8K word block of program memory. The CALL

and GOTO instructions provide only 11 bits of address

to allow branching within any 2K program memory

page. When doing a CALL or GOTO instruction the

upper 2 bits of the address are provided by

PCLATH<4:3>. When doing a CALL or GOTO instruc-

tion, the user must ensure that the page select bits are

programmed so that the desired program memory

page is addressed. If a return from a CALL instruction

(or interrupt) is executed, the entire 13-bit PC is pushed

onto

the

stack.

Therefore,

manipulation of

the

PCLATH<4:3> bits are not required for the return

instructions (which POPs the address from the stack).

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