PIC16F1507 datasheet(16/266 Pages) MICROCHIP

16 / 266 page

 2011 Microchip Technology Inc.

Preliminary

DS41586A-page 16

PIC16(L)F1507

FIGURE 3-1:

PROGRAM MEMORY MAP

AND STACK FOR

PIC16(L)F1507

3.1.1

READING PROGRAM MEMORY AS

DATA

There are two methods of accessing constants in pro-

gram memory. The first method is to use tables of

RETLW

instructions. The second method is to set an

FSR to point to the program memory.

3.1.1.1

RETLW

Instruction

The RETLW instruction can be used to provide access

to tables of constants. The recommended way to create

such a table is shown in Example 3-1.

EXAMPLE 3-1:

RETLW

INSTRUCTION

The BRW instruction makes this type of table very sim-

ple to implement. If your code must remain portable

with previous generations of microcontrollers, then the

BRW

instruction is not available so the older table read

method must be used.

PC<14:0>

0000h

0004h

Stack Level 0

Stack Level 15

Reset Vector

Interrupt Vector

Stack Level 1

0005h

On-chip

Program

Memory

Page 0

07FFh

Wraps to Page 0

0800h

CALL

, CALLW

RETURN

, RETLW

Interrupt, RETFIE

Rollover to Page 0

7FFFh

constants

BRW

;Add Index in W to

;program counter to

;select data

RETLW DATA0

;Index0 data

RETLW DATA1

;Index1 data

RETLW DATA2

RETLW DATA3

my_function

;… LOTS OF CODE…

MOVLW

DATA_INDEX

call constants

;… THE CONSTANT IS IN W

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