10F222 datasheet(21/86 Pages) MICROCHIP

21 / 86 page

DS41270E-page 19

PIC10F220/222

4.7

Program Counter

As a program instruction is executed, the Program

Counter (PC) will contain the address of the next

program instruction to be executed. The PC value is

increased by one every instruction cycle, unless an

instruction changes the PC.

For a GOTO instruction, bits 8:0 of the PC are provided

by the GOTO instruction word. The PC Latch (PCL) is

mapped to PC<7:0>.

For a CALL instruction or any instruction where the PCL

is the destination, bits 7:0 of the PC again are provided

by the instruction word. However, PC<8> does not

come from the instruction word, but is always cleared

(Figure 4-5).

Instructions where the PCL is the destination or Modify

PCL instructions, include MOVWF PC, ADDWF PC and

BSF PC

, 5.

FIGURE 4-5:

LOADING OF PC

BRANCH INSTRUCTIONS

4.7.1

EFFECTS OF RESET

The PC is set upon a Reset, which means that the PC

addresses the last location in program memory (i.e.,

the oscillator calibration instruction). After executing

MOVLW XX

, the PC will roll over to location 0000h and

begin executing user code.

4.8

Stack

The PIC10F220 device has a 2-deep, 8-bit wide

hardware PUSH/POP stack.

The PIC10F222 device has a 2-deep, 9-bit wide

hardware PUSH/POP stack.

A CALL instruction will PUSH the current value of stack

1 into stack 2 and then PUSH the current PC value,

incremented by one, into stack level 1. If more than two

sequential CALL’s are executed, only the most recent

two return addresses are stored.

A RETLW instruction will POP the contents of stack level

1 into the PC and then copy stack level 2 contents into

level 1. If more than two sequential RETLW’s are exe-

cuted, the stack will be filled with the address

previously stored in level 2.

Note:

Because PC<8> is cleared in the CALL

instruction or any Modify PCL instruction,

all subroutine calls or computed jumps are

limited to the first 256 locations of any

program memory page (512 words long).

PCL

Instruction Word

GOTO

Instruction

CALL

or Modify PCL Instruction

PCL

Instruction Word

Reset to ‘0’

Note 1: The W register will be loaded with the lit-

eral value specified in the instruction. This

is particularly useful for the implementa-

tion of data look-up tables within the

program memory.

2: There are no Status bits to indicate stack

overflows or stack underflow conditions.

3: There are no instructions mnemonics

called PUSH or POP. These are actions

that occur from the execution of the CALL

and RETLW instructions.

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