PIC16F872 Datasheet, PDF (33/160 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS FLASH Microcontroller

PIC16F872
4.6 Writing to the FLASH Program
Memory
When the PIC16F872 is fully code protected or not
code protected, a word of the FLASH program memory
may be written provided the WRT configuration bit is
set. If the PIC16F872 is 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 control 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
Required
Sequence
BCF
MOVLW
MOVWF
MOVLW
MOVWF
BSF
INTCON, GIE
55h
EECON2
AAh
EECON2
EECON1, WR
; Disable Interrupts
;
; Write 55h
;
; Write AAh
; Set WR bit to begin write
NOP
NOP
BSF INTCON, GIE
BCF EECON1, WREN
; Instructions here are ignored by the microcontroller
; Microcontroller will halt operation and wait for
; a write complete. After the write
; the microcontroller continues with 3rd instruction
; Enable Interrupts
; Disable writes
© 1999 Microchip Technology Inc.
Preliminary
DS30221A-page 33