PIC16F870SLASHP datasheet(43/156 Pages) MICROCHIP

43 / 156 page

Preliminary

DS30569A-page 43

PIC16F870/871

4.6

Writing to the FLASH Program

Memory

When the PIC16F870/871 are fully code protected or

not code protected, a word of the FLASH program

memory may be written provided the WRT configura-

tion bit is set. If the PIC16F870/871 are partially code

protected, then a word of FLASH program memory

may be written if the word is in a non-code protected

segment of memory and the WRT configuration bit is

set. To write a FLASH program location, the first two

bytes of the address must be written to the EEADR and

EEADRH registers and two bytes of the data to the

EEDATA and EEDATH registers, set the EEPGD con-

trol bit (EECON1<7>), and then set control bit WR

(EECON1<1>). The sequence in Example 4-4 must be

followed to initiate a write to program memory.

The microcontroller will then halt internal operations

during the next two instruction cycles for the TPEW

(parameter D133) in which the write takes place. This

is not SLEEP mode, as the clocks and peripherals will

continue to run. Therefore, the two instructions follow-

ing the “BSF EECON, WR” should be NOP instructions.

After the write cycle, the microcontroller will resume

operation with the 3rd instruction after the EECON1

write instruction.

EXAMPLE 4-4:

FLASH PROGRAM WRITE

BSF

STATUS, RP1

;

BCF

STATUS, RP0

; Bank 2

MOVLW

ADDRH

;

MOVWF

EEADRH

; MSByte of Program Address to read

MOVLW

ADDRL

;

MOVWF

EEADR

; LSByte of Program Address to read

MOVLW

DATAH

;

MOVWF

EEDATH

; MS Program Memory Value to write

MOVLW

DATAL

;

MOVWF

EEDATA

; LS Program Memory Value to write

BSF

STATUS, RP0

; Bank 3

BSF

EECON1, EEPGD

; Point to PROGRAM memory

BSF

EECON1, WREN

; Enable writes

BCF

INTCON, GIE

; Disable Interrupts

MOVLW

55h

;

Required

MOVWF

EECON2

; Write 55h

Sequence

MOVLW

AAh

;

MOVWF

EECON2

; Write AAh

BSF

EECON1, WR

; Set WR bit to begin write

NOP

; Instructions here are ignored by the microcontroller

NOP

; Microcontroller will halt operation and wait for

; a write complete. After the write

; the microcontroller continues with 3rd instruction

BSF

INTCON,

GIE

; Enable Interrupts

BCF

EECON1, WREN

; Disable writes

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