PIC18F4680ISPQTP datasheet(101/482 Pages) MICROCHIP

101 / 482 page

Preliminary

DS39625C-page 99

PIC18F2585/2680/4585/4680

6.3

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 6-4

shows the interface between the internal program

memory and the TABLAT.

FIGURE 6-4:

READS FROM FLASH PROGRAM MEMORY

EXAMPLE 6-1:

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

CODE_ADDR_UPPER

; Load TBLPTR with the base

MOVWF

TBLPTRU

; address of the word

MOVLW

CODE_ADDR_HIGH

MOVWF

TBLPTRH

MOVLW

CODE_ADDR_LOW

MOVWF

TBLPTRL

READ_WORD

TBLRD*+

; read into TABLAT and increment

MOVF

TABLAT, W

; get data

MOVWF

WORD_EVEN

TBLRD*+

; read into TABLAT and increment

MOVF

TABLAT, W

; get data

MOVF

WORD_ODD

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