PIC16F87X
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.
4.6
Writing to the FLASH Program
Memory
A word of the FLASH program memory may only be
written to if the word is in a non-code protected seg-
ment 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-
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 NOPinstructions.
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
STATUS, RP0
ADDRH
;
BCF
; Bank 2
;
MOVLW
MOVWF
MOVLW
MOVWF
MOVLW
MOVWF
MOVLW
MOVWF
BSF
EEADRH
; MSByte of Program Address to read
ADDRL
;
EEADR
; LSByte of Program Address to read
DATAH
;
EEDATH
; MS Program Memory Value to write
;
DATAL
EEDATA
; LS Program Memory Value to write
; Bank 3
STATUS, RP0
EECON1, EEPGD
EECON1, WREN
BSF
; Point to PROGRAM memory
; Enable writes
BSF
BCF
INTCON, GIE
55h
; Disable Interrupts
MOVLW
MOVWF
MOVLW
MOVWF
BSF
;
Required
Sequence
EECON2
AAh
; Write 55h
;
EECON2
EECON1, WR
; Write AAh
; Set WR bit to begin write
NOP
NOP
; 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
BSF
BCF
INTCON, GIE
EECON1, WREN
; Disable writes
4.7
Write Verify
Depending on the application, good programming prac-
tice 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.
Generally a write failure will be a bit which was written
as a '1', but reads back as a '0' (due to leakage off the
bit).
1999 Microchip Technology Inc.
DS30292B-page 45
ETC [ ETC ]
