PIC18F23K20-ESLASHML datasheet(94/456 Pages) MICROCHIP

94 / 456 page

PIC18F2XK20/4XK20

DS41303G-page 94

 2010 Microchip Technology Inc.

6.4

Erasing Flash Program Memory

The minimum erase block is 32 words or 64 bytes. Only

through the use of an external programmer, or through

ICSP™ control, can larger blocks of program memory

be bulk erased. Word erase in the Flash array is not

supported.

When initiating an erase sequence from the Microcon-

troller itself, a block of 64 bytes of program memory is

erased.

The

Most

Significant

bits

the

TBLPTR<21:6> point to the block being erased. The

TBLPTR<5:0> bits are ignored.

The EECON1 register commands the erase operation.

The EEPGD bit must be set to point to the Flash pro-

gram memory. The WREN bit must be set to enable

write operations. The FREE bit is set to select an erase

operation.

The write initiate sequence for EECON2, shown as

steps 4 through 6 in Section 6.4.1 “Flash Program

Memory Erase Sequence”, is used to guard against

accidental writes. This is sometimes referred to as a

long write.

A long write is necessary for erasing the internal Flash.

Instruction execution is halted during the long write

cycle. The long write is terminated by the internal pro-

gramming timer.

6.4.1

FLASH PROGRAM MEMORY

ERASE SEQUENCE

The sequence of events for erasing a block of internal

program memory is:

Load Table Pointer register with address of

block being erased.

Set the EECON1 register for the erase operation:

• set EEPGD bit to point to program memory;

• clear the CFGS bit to access program memory;

• set WREN bit to enable writes;

• set FREE bit to enable the erase.

Disable interrupts.

Write 55h to EECON2.

Write 0AAh to EECON2.

Set the WR bit. This will begin the block erase

cycle.

The CPU will stall for duration of the erase

(about 2 ms using internal timer).

Re-enable interrupts.

EXAMPLE 6-2:

ERASING A FLASH PROGRAM MEMORY BLOCK

MOVLW

CODE_ADDR_UPPER

; load TBLPTR with the base

MOVWF

TBLPTRU

; address of the memory block

MOVLW

CODE_ADDR_HIGH

MOVWF

TBLPTRH

MOVLW

CODE_ADDR_LOW

MOVWF

TBLPTRL

ERASE_BLOCK

BSF

EECON1, EEPGD

; point to Flash program memory

BCF

EECON1, CFGS

; access Flash program memory

BSF

EECON1, WREN

; enable write to memory

BSF

EECON1, FREE

; enable block Erase operation

BCF

INTCON, GIE

; disable interrupts

Required

MOVLW

55h

Sequence

MOVWF

EECON2

; write 55h

MOVLW

0AAh

MOVWF

EECON2

; write 0AAh

BSF

EECON1, WR

; start erase (CPU stall)

BSF

INTCON, GIE

; re-enable interrupts

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