PIC16F18345 datasheet(19/442 Pages) MICROCHIP

19 / 442 page

 2015 Microchip Technology Inc.

Preliminary

DS40001799A-page 19

PIC16(L)F18313/18323

FIGURE 3-1:

PROGRAM MEMORY MAP

AND STACK FOR

PIC16(L)F18313/18323

3.1.1

READING PROGRAM MEMORY AS

DATA

There are two methods of accessing constants in

program 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

simple to implement. If your code must remain portable

with previous generations of microcontrollers, the older

table read method must be used because the BRW

instruction is not available in some devices, such as the

PIC16F6XX,

PIC16F7XX,

PIC16F8XX,

and

PIC16F9XX devices.

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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