PIC12F1840 データシートの表示（PDF） - Microchip Technology

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PIC12F1840

8-Pin Flash Microcontrollers with XLP Technology

Microchip Technology 

PIC12(L)F1840

FIGURE 3-1:

PROGRAM MEMORY MAP

AND STACK FOR

PIC12(L)F1840

PC<14:0>

CALL, CALLW

15

RETURN, RETLW

Interrupt, RETFIE

Stack Level 0

Stack Level 1

Stack Level 15

Reset Vector

0000h

On-chip

Program

Memory

Interrupt Vector

Page 0

Page 1

Rollover to Page 0

0004h

0005h

07FFh

0800h

0FFFh

1000h

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:

constants

BRW

RETLW DATA0

RETLW DATA1

RETLW DATA2

RETLW DATA3

RETLW INSTRUCTION

;Add Index in W to

;program counter to

;select data

;Index0 data

;Index1 data

my_function

;… LOTS OF CODE…

MOVLW

DATA_INDEX

call constants

;… THE CONSTANT IS IN W

The BRW instruction makes this type of table very

simple 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.

Rollover to Page 1

7FFFh

DS41441C-page 14

 2011-2012 Microchip Technology Inc.

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