PIC17C752-08SLASHCL datasheet(52/328 Pages) MICROCHIP

52 / 328 page

PIC17C7XX

DS30289A-page 52

7.3

Stack Operation

PIC17C7XX devices have a 16 x 16-bit hardware stack

(Figure 7-1). The stack is not part of either the program

or data memory space, and the stack pointer is neither

readable nor writable. The PC (Program Counter) is

“PUSHed” onto the stack when a CALL or LCALL

instruction is executed or an interrupt is acknowledged.

The stack is “POPed” in the event of a RETURN, RETLW,

or a RETFIE instruction execution. PCLATH is not

affected by a “PUSH” or a “POP” operation.

The stack operates as a circular buffer, with the stack

pointer initialized to '0' after all resets. There is a stack

available bit (STKAV) to allow software to ensure that

the stack will not overﬂow. The STKAV bit is set after a

device reset. When the stack pointer equals Fh, STKAV

is cleared. When the stack pointer rolls over from Fh to

0h, the STKAV bit will be held clear until a device reset.

After the device is “PUSHed” sixteen times (without a

“POP”), the seventeenth push overwrites the value

from the ﬁrst push. The eighteenth push overwrites the

second push (and so on).

Note 1: There is not a status bit for stack under-

ﬂow. The STKAV bit can be used to detect

the underﬂow which results in the stack

pointer being at the top of stack.

Note 2: There are no instruction mnemonics

called PUSH or POP. These are actions

that occur from the execution of the CALL,

RETURN

, RETLW, and RETFIE instruc-

tions, or the vectoring to an interrupt vec-

tor.

Note 3: After a reset, if a “POP” operation occurs

before a “PUSH” operation, the STKAV bit

will be cleared. This will appear as if the

stack is full (underﬂow has occurred). If a

“PUSH” operation occurs next (before

another “POP”), the STKAV bit will be

locked clear. Only a device reset will

cause this bit to set.

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