PIC18F2450/4450
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.
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.
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
Program Memory
(Even Byte Address)
(Odd Byte Address)
TBLPTR = xxxxx1
TBLPTR = xxxxx0
Instruction Register
TABLAT
Read Register
FETCH
TBLRD
(IR)
EXAMPLE 6-1:
READING A FLASH PROGRAM MEMORY WORD
MOVLW
CODE_ADDR_UPPER
TBLPTRU
CODE_ADDR_HIGH
TBLPTRH
CODE_ADDR_LOW
TBLPTRL
; Load TBLPTR with the base
; address of the word
MOVWF
MOVLW
MOVWF
MOVLW
MOVWF
READ_WORD
TBLRD*+
MOVF
MOVWF
TBLRD*+
MOVF
; read into TABLAT and increment
; get data
TABLAT, W
WORD_EVEN
; read into TABLAT and increment
; get data
TABLAT, W
WORD_ODD
MOVF
© 2006 Microchip Technology Inc.
Advance Information
DS39760A-page 77
MICROCHIP [ MICROCHIP ]
