PIC16C72-04SLASHSP datasheet(16/124 Pages) MICROCHIP

16 / 124 page

PIC16C72 Series

DS39016A-page 16

Preliminary

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). An example of the overwriting of the stack is

shown in Figure 2-10.

FIGURE 2-10: STACK MODIFICATION

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 2 bits of the address are provided by

PCLATH<4:3>. When doing a CALL or GOTO instruction,

the user must ensure that the page select bits are 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

the

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

instructions (which POPs the address from the stack).

Push1 Push9

Push2 Push10

Push3

Push4

Push5

Push6

Push7

Push8

Top of STACK

STACK

Note:

PIC16C72 Series devices ignore paging

bit PCLATH<4>. The use of PCLATH<4>

as a general purpose read/write bit is not

recommended

since

this

may

affect

upward compatibility with future products.

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