PIC18F258 MICROCHIP [Microchip Technology], PIC18F258 Datasheet - Page 71

• Manufacturer Part Number: PIC18F258
• Description: High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN
• Manufacturer: MICROCHIP [Microchip Technology]

6.3
The TBLRD instruction is used to retrieve data from pro-
gram memory and place into data RAM. Table Reads
from program memory are performed one byte at a
time.
FIGURE 6-4:
EXAMPLE 6-1:
 2002 Microchip Technology Inc.
READ_WORD
Reading the FLASH Program
Memory
Instruction Register
MOVLW CODE_ADDR_UPPER
MOVWF TBLPTRU
MOVLW CODE_ADDR_HIGH
MOVWF TBLPTRH
MOVLW CODE_ADDR_LOW
MOVWF TBLPTRL
TBLRD*+
MOVF TABLAT, W
MOVWF WORD_LSB
TBLRD*+
MOVF TABLAT, W
MOVWF WORD_MSB
(IR)
READS FROM FLASH PROGRAM MEMORY
READING A FLASH PROGRAM MEMORY WORD
(Even Byte Address)
FETCH
Program Memory
Preliminary
; Load TBLPTR with the base
; address of the word
; read into TABLAT and increment
; get data
; read into TABLAT and increment
; get data
(Odd Byte Address)
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.
TBLPTR = xxxxx1
TBLRD
Read Register
PIC18FXX8
TABLAT
TBLPTR = xxxxx0
DS41159B-page 69