PIC16C54-04SLASHP datasheet(17/84 Pages) MICROCHIP

17 / 84 page

Preliminary

DS40191A-page 17

PIC16CR54C

4.5

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> (Figure 4-5 and Figure 4-6).

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 4-10 and Figure 4-11)/

Instructions where the PCL is the destination, or

Modify PCL instructions, include MOVWF PC, ADDWF

, and BSF PC, 5.

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 pro-

gram memory page (512 words long).

FIGURE 4-5:

LOADING OF PC

BRANCH INSTRUCTIONS -

PIC16CR54C

4.5.1

EFFECTS OF RESET

The Program Counter is set upon a RESET, which

means that the PC addresses the last location in the

last page i.e., the reset vector.

The STATUS register page preselect bits are cleared

upon a RESET, which means that page 0 is

pre-selected.

Therefore, upon a RESET, a GOTO instruction at the

reset vector location will automatically cause the

program to jump to page 0.

4.6

Stack

PIC16CR54C device has a 9-bit, two-level hardware

push/pop stack (Figure 4-1).

A CALL instruction will

push the current value of stack

1 into stack 2 and then push the current program

counter 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 program counter and then copy stack level 2

contents into level 1. If more than two sequential

RETLW

’s are executed, the stack will be filled with the

address previously stored in level 2. Note that the

W register will be loaded with the literal value speciﬁed

in the instruction. This is particularly useful for the

implementation of data look-up tables within the

program memory.

PCL

Reset to '0'

Instruction Word

GOTO

Instruction

CALL

or Modify PCL Instruction

PIC16C54-04/P Datasheet(PDF) 17 Page - Microchip Technology

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