Datasheet

 2012 Microchip Technology Inc. DS30575A-page 151
PIC18F97J94 FAMILY
7.5.2 FLASH PROGRAM MEMORY WRITE
SEQUENCE (WORD PROGRAMMING)
The PIC18F97J94 family of devices has a feature that
allows programming a single word (two bytes). This
feature is enabled when the WWPROG bit is set. If the
memory location is already erased, the following
sequence is required to enable this feature:
1. Load the Table Pointer register with the address
of the data to be written. (It must be an even
address.)
2. Write the 2 bytes into the holding registers by
performing table writes. (Do not post-increment
on the second table write).
3. Set the WREN bit (EECON1<2>) to enable
writes and the WWPROG bit (EECON1<5>) to
select Word Write mode.
4. Disable interrupts.
5. Write 55h to EECON2.
6. Write 0AAh to EECON2.
7. Set the WR bit; this will begin the write cycle.
8. The CPU will stall for the duration of the write for
T
IW (see Parameter D133A).
9. Re-enable interrupts.
EXAMPLE 7-4: SINGLE-WORD WRITE TO FLASH PROGRAM MEMORY
MOVLW CODE_ADDR_UPPER ; Load TBLPTR with the base address
MOVWF TBLPTRU
MOVLW CODE_ADDR_HIGH
MOVWF TBLPTRH
MOVLW CODE_ADDR_LOW ; The table pointer must be loaded with an even address
MOVWF TBLPTRL
MOVLW DATA0 ; LSB of word to be written
MOVWF TABLAT
TBLWT*+
MOVLW DATA1 ; MSB of word to be written
MOVWF TABLAT
TBLWT* ; The last table write must not increment the
table pointer! The table pointer needs to
point to the MSB before starting the write operation.
PROGRAM_MEMORY
BSF EECON1, WWPROG ; enable single word write
BSF EECON1, WREN ; enable write to memory
BCF INTCON, GIE ; disable interrupts
MOVLW 55h
Required MOVWF EECON2 ; write 55h
Sequence MOVLW 0AAh
MOVWF EECON2 ; write AAh
BSF EECON1, WR ; start program (CPU stall)
BSF INTCON, GIE ; re-enable interrupts
BCF EECON1, WWPROG ; disable single word write
BCF EECON1, WREN ; disable write to memory