18F8680 datasheet(92/496 Pages) MICROCHIP

92 / 496 page

PIC18F6585/8585/6680/8680

DS30491C-page 90

 2004 Microchip Technology Inc.

5.5.1

FLASH PROGRAM MEMORY WRITE

SEQUENCE

The sequence of events for programming an internal

program memory location should be:

Read 64 bytes into RAM.

Update data values in RAM as necessary.

Load table pointer with address being erased.

Do the row erase procedure.

Load table pointer with address of first byte

being written.

Write the first 8 bytes into the holding registers

with auto-increment.

Set the EECON1 register for the write operation:

• set EEPGD bit to point to program memory;

• clear the CFGS bit to access program memory;

• set WREN to enable byte writes.

Disable interrupts.

Write 55h to EECON2.

10. Write 0AAh to EECON2.

11. Set the WR bit. This will begin the write cycle.

12. The CPU will stall for duration of the write (about

5 ms using internal timer).

13. Execute a NOP.

14. Re-enable interrupts.

15. Repeat steps 6-14 seven times to write 64 bytes.

16. Verify the memory (table read).

This procedure will require about 40 ms to update one

row of 64 bytes of memory. An example of the required

code is given in Example 5-3.

EXAMPLE 5-3:

WRITING TO FLASH PROGRAM MEMORY

Note:

Before setting the WR bit, the Table

Pointer address needs to be within the

intended address range of the eight bytes

in the holding register.

MOVLW

D’64

; number of bytes in erase block

MOVWF

COUNTER

MOVLW

high(BUFFER_ADDR)

; point to buffer

MOVWF

FSR0H

MOVLW

low(BUFFER_ADDR)

MOVWF

FSR0L

MOVLW

upper(CODE_ADDR)

; Load TBLPTR with the base

MOVWF

TBLPTRU

; address of the memory block

MOVLW

high(CODE_ADDR)

MOVWF

TBLPTRH

MOVLW

low(CODE_ADDR)

MOVWF

TBLPTRL

READ_BLOCK

TBLRD*+

; read into TABLAT, and inc

MOVF

TABLAT, W

; get data

MOVWF

POSTINC0

; store data

DECFSZ

COUNTER

; done?

BRA

READ_BLOCK

; repeat

MODIFY_WORD

MOVLW

high(DATA_ADDR)

; point to buffer

MOVWF

FSR0H

MOVLW

low(DATA_ADDR)

MOVWF

FSR0L

MOVLW

low(NEW_DATA)

; update buffer word

MOVWF

POSTINC0

MOVLW

high(NEW_DATA)

MOVWF

INDF0

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