PIC18F258-ESLASHLSQTP datasheet(75/402 Pages) MICROCHIP

75 / 402 page

DS41159E-page 73

PIC18FXX8

EXAMPLE 6-3:

WRITING TO FLASH PROGRAM MEMORY (CONTINUED)

6.5.2

WRITE VERIFY

Depending on the application, good programming

practice may dictate that the value written to the

memory should be verified against the original value.

This should be used in applications where excessive

writes can stress bits near the specification limit.

6.5.3

UNEXPECTED TERMINATION OF

WRITE OPERATION

If a write is terminated by an unplanned event, such as

loss of power or an unexpected Reset, the memory

location just programmed should be verified and repro-

grammed if needed.The WRERR bit is set when a write

operation is interrupted by a MCLR Reset or a WDT

Time-out Reset during normal operation. In these

situations, users can check the WRERR bit and rewrite

the location.

6.5.4

PROTECTION AGAINST SPURIOUS

WRITES

To reduce the probability against spurious writes to

Flash program memory, the write initiate sequence

must also be followed. See Section 24.0 “Special

Features of the CPU” for more detail.

6.6

Flash Program Operation During

Code Protection

See Section 24.0 “Special Features of the CPU” for

details on code protection of Flash program memory.

WRITE_WORD_TO_HREGS

MOVFW

POSTINC0, W

; get low byte of buffer data

MOVWF

TABLAT

; present data to table latch

TBLWT+*

; write data, perform a short write

; to internal TBLWT holding register.

DECFSZ

COUNTER

; loop until buffers are full

BRA

WRITE_WORD_TO_HREGS

PROGRAM_MEMORY

BSF

EECON1, EEPGD

; point to FLASH program memory

BCF

EECON1, CFGS

; access FLASH program memory

BSF

EECON1, WREN

; enable write to memory

BCF

INTCON, GIE

; disable interrupts

MOVLW

55h

; write 55h

Required

MOVWF

EECON2

Sequence

MOVLW

0AAh

; write 0AAh

MOVWF

EECON2

; start program (CPU stall)

BSF

EECON1, WR

NOP

BSF

INTCON, GIE

; re-enable interrupts

DECFSZ

COUNTER_HI

; loop until done

BRA

PROGRAM_LOOP

BCF

EECON1, WREN

; disable write to memory

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