Microchip Technology DM183037 Data Sheet

Page of 696
 2012 Microchip Technology Inc.
DS30575A-page 147
PIC18F97J94 FAMILY
7.3
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.
The TBLPTR points to a byte address in program
space. Executing TBLRD places the byte pointed to into
TABLAT. In addition, the 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. 
 shows the interface between the internal
program memory and the TABLAT.
FIGURE 7-4:
READS FROM FLASH PROGRAM MEMORY 
EXAMPLE 7-1:
READING A FLASH PROGRAM MEMORY WORD 
(Even Byte Address)
Program Memory
(Odd Byte Address)
TBLRD
TBLPTR = xxxxx1
FETCH
Instruction Register
(IR)
TBLPTR = xxxxx0
TABLAT
Read Register
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
MOVWF
WORD_ODD