PIC16F8X_13 Datasheet, PDF (35/128 Pages) Microchip Technology – 18-pin Flash/EEPROM 8-Bit Microcontrollers

PIC16F8X
7.5 Write Verify
Depending on the application, good programming prac-
tice may dictate that the value written to the Data
EEPROM should be verified (Example 7-1) to the
desired value to be written. This should be used in
applications where an EEPROM bit will be stressed
near the specification limit. The Total Endurance disk
will help determine your comfort level.
SUBWF EEDATA, W
BTFSS STATUS, Z
GOTO WRITE_ERR
:
:
;
; Is difference 0?
; NO, Write error
; YES, Good write
; Continue program
7.6 Protection Against Spurious Writes
There are conditions when the device may not want to
write to the data EEPROM memory. To protect against
Generally the EEPROM write failure will be a bit which
was written as a '1', but reads back as a '0' (due to
leakage off the bit).
spurious EEPROM writes, various mechanisms have
been built in. On power-up, WREN is cleared. Also, the
Power-up Timer (72 ms duration) prevents
EEPROM write.
EXAMPLE 7-1: WRITE VERIFY
BCF STATUS, RP0 ; Bank 0
:
; Any code can go here
The write initiate sequence and the WREN bit together
help prevent an accidental write during brown-out,
power glitch, or software malfunction.
:
;
MOVF EEDATA, W ; Must be in Bank 0
BSF STATUS, RP0 ; Bank 1
7.7 Data EEPROM Operation during Code
Protect
READ
BSF
EECON1, RD ; YES, Read the
; value written
When the device is code protected, the CPU is able to
read and write unscrambled data to the Data EEPROM.
BCF STATUS, RP0 ; Bank 0
;
; Is the value written (in W reg) and
; read (in EEDATA) the same?
For ROM devices, there are two code protection bits
(Section 8.1). One for the ROM program memory and
one for the Data EEPROM memory.
;
TABLE 7-1
REGISTERS/BITS ASSOCIATED WITH DATA EEPROM
Address Name
Bit 7
Bit 6 Bit 5 Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value on
Power-on
Reset
Value on all
other resets
08h
EEDATA EEPROM data register
09h
EEADR EEPROM address register
88h
EECON1
—
—
—
EEIF WRERR WREN
WR
89h
EECON2 EEPROM control register 2
xxxx xxxx uuuu uuuu
xxxx xxxx uuuu uuuu
RD
---0 x000 ---0 q000
---- ---- ---- ----
Legend: x = unknown, u = unchanged, - = unimplemented read as '0', q = value depends upon condition. Shaded cells are not
used by Data EEPROM.
 1996-2013 Microchip Technology Inc.
DS30430D-page 35