PIC16F87XA
DS39582B-page 38
2003 Microchip Technology Inc.
An example of the complete four-word write sequence
is shown in Example 3-4. The initial address is loaded
into the EEADRH:EEADR register pair; the four words
of data are loaded using indirect addressing.
EXAMPLE 3-4:
WRITING TO FLASH PROGRAM MEMORY
; This write routine assumes the following:
;
; 1. A valid starting address (the least significant bits = ‘00’)is loaded in ADDRH:ADDRL
; 2. The 8 bytes of data are loaded, starting at the address in DATADDR
; 3. ADDRH, ADDRL and DATADDR are all located in shared data memory 0x70 - 0x7f
;
BSF
STATUS,RP1
;
BCF
STATUS,RP0
; Bank 2
MOVF
ADDRH,W
; Load initial address
MOVWF
EEADRH
;
MOVF
ADDRL,W
;
MOVWF
EEADR
;
MOVF
DATAADDR,W
; Load initial data address
MOVWF
FSR
;
LOOP
MOVF
INDF,W
; Load first data byte into lower
MOVWF
EEDATA
;
INCF
FSR,F
; Next byte
MOVF
INDF,W
; Load second data byte into upper
MOVWF
EEDATH
;
INCF
FSR,F
;
BSF
STATUS,RP0
; Bank 3
BSF
EECON1,EEPGD
; Point to program memory
BSF
EECON1,WREN
; Enable writes
BCF
INTCON,GIE
; Disable interrupts (if using)
MOVLW
55h
; Start of required write sequence:
MOVWF
EECON2
; Write 55h
MOVLW
AAh
;
MOVWF
EECON2
; Write AAh
BSF
EECON1,WR
; Set WR bit to begin write
NOP
; Any instructions here are ignored as processor
; halts to begin write sequence
NOP
; processor will stop here and wait for write complete
; after write processor continues with 3rd instruction
BCF
EECON1,WREN
; Disable writes
BSF
INTCON,GIE
; Enable interrupts (if using)
BCF
STATUS,RP0
; Bank 2
INCF
EEADR,F
; Increment address
MOVF
EEADR,W
; Check if lower two bits of address are ‘00’
ANDLW
0x03
; Indicates when four words have been programmed
XORLW
0x03
;
BTFSC
STATUS,Z
; Exit if more than four words,
GOTO
LOOP
; Continue if less than four words
R
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