PIC16F628-20SLASHSS datasheet(25/160 Pages) MICROCHIP

25 / 160 page

Preliminary

DS40300B-page 25

PIC16F62X

4.3

PCL and PCLATH

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 4-7 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>

→ PCH). The lower example in the figure

shows how the PC is loaded during a CALL or GOTO

instruction (PCLATH<4:3>

→ PCH).

FIGURE 4-7:

LOADING OF PC IN

DIFFERENT SITUATIONS

4.3.1

COMPUTED GOTO

A computed GOTO is accomplished by adding an offset

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).

PCLATH<4:0>

PCLATH

Instruction with

ALU result

GOTO, CALL

Opcode <10:0>

11 10

PCLATH<4:3>

PCH

PCL

PCLATH

PCH

PCL

PCL as

Destination

4.3.2

STACK

The PIC16F62X family has an 8 level deep x 13-bit

wide hardware stack (Figure 4-1 and Figure 4-2). 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 RET-

FIE

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).

Note 1:

There are no STATUS bits to

indicate stack overflow 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, RETURN, RETLW

and RETFIE

instructions, or the vectoring to an

interrupt address.

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