18F8680 datasheet(89/496 Pages) MICROCHIP

89 / 496 page

 2004 Microchip Technology Inc.

DS30491C-page 87

PIC18F6585/8585/6680/8680

5.3

Reading the Flash Program

Memory

The TBLRD instruction is used to retrieve data from

program memory and places it into data RAM. Table

reads from program memory are performed one byte at

a time.

TBLPTR points to a byte address in program space.

Executing TBLRD places the byte pointed to into

TABLAT. In addition, TBLPTR can be modified

automatically for the next table read operation.

The internal program memory is typically organized by

words. The Least Significant bit of the address selects

between the high and low bytes of the word. Figure 5-4

shows the interface between the internal program

memory and the TABLAT.

FIGURE 5-4:

READS FROM FLASH PROGRAM MEMORY

EXAMPLE 5-1:

READING A FLASH PROGRAM MEMORY WORD

(Even Byte Address)

Program Memory

(Odd Byte Address)

TBLRD

TABLAT

TBLPTR = xxxxx1

FETCH

Instruction Register

(IR)

Read Register

TBLPTR = xxxxx0

MOVLW

upper(CODE_ADDR)

; Load TBLPTR with the base

MOVWF

TBLPTRU

; address of the word

MOVLW

high(CODE_ADDR)

MOVWF

TBLPTRH

MOVLW

low(CODE_ADDR_LOW)

MOVWF

TBLPTRL

READ_WORD

TBLRD*+

; read into TABLAT and increment

MOVF

TABLAT, W

; get data

MOVWF

LSB

TBLRD*+

; read into TABLAT and increment

MOVF

TABLAT, W

; get data

MOVWF

MSB

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