PIC18F1220_07 Datasheet, PDF (63/308 Pages) Microchip Technology – 18/20/28-Pin High-Performance, Enhanced Flash Microcontrollers with 10-bit A/D and nanoWatt Technology

PIC18F1220/1320
6.3 Reading the Flash Program
Memory
The TBLRD instruction is used to retrieve data from
program memory and place 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 a TBLRD instruction 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
Program Memory
Odd (High) Byte Even (Low) Byte
Instruction Register
(IR)
TBLPTR
LSB = 1
TBLPTR
LSB = 0
TABLAT
Read Register
EXAMPLE 6-1: READING A FLASH PROGRAM MEMORY WORD
READ_WORD
MOVLW
MOVWF
MOVLW
MOVWF
MOVLW
MOVWF
TBLRD*+
MOVFW
MOVWF
TBLRD*+
MOVFW
MOVWF
CODE_ADDR_UPPER
TBLPTRU
CODE_ADDR_HIGH
TBLPTRH
CODE_ADDR_LOW
TBLPTRL
TABLAT
WORD_EVEN
TABLAT
WORD_ODD
; Load TBLPTR with the base
; address of the word
; read into TABLAT and increment TBLPTR
; get data
; read into TABLAT and increment TBLPTR
; get data
© 2007 Microchip Technology Inc.
DS39605F-page 61