PIC16F684
10.5 Protection Against Spurious Write
10.6 Data EEPROM Operation During
Code-Protect
There are conditions when the user may not want to
write to the data EEPROM memory. To protect against
spurious EEPROM writes, various mechanisms have
been built in. On power-up, WREN is cleared. Also, the
Data memory can be code-protected by programming
the CPD bit in the Configuration Word register
(Register 12-1) to ‘0’.
Power-up
Timer
(64 ms
duration)
prevents
When the data memory is code-protected, the CPU is
able to read and write data to the data EEPROM. It is
recommended to code-protect the program memory
when code-protecting data memory. This prevents
anyone from programming zeroes over the existing
code (which will execute as NOPs) to reach an added
routine, programmed in unused program memory,
which outputs the contents of data memory.
Programming unused locations in program memory to
‘0’ will also help prevent data memory code protection
from becoming breached.
EEPROM write.
The write initiate sequence and the WREN bit together
help prevent an accidental write during:
• Brown-out
• Power Glitch
• Software Malfunction
TABLE 10-1: REGISTERS/BITS ASSOCIATED WITH DATA EEPROM
Value on
all other
Resets
Value on
POR, BOD
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0Bh/8Bh
0Ch
INTCON
PIR1
GIE
EEIF
EEIE
PEIE
ADIF
ADIE
T0IE
INTE
C2IF
C2IE
RAIE
C1IF
C1IE
T0IF
INTF
RAIF 0000 0000 0000 0000
CCP1IF
CCP1IE
OSFIF TMR2IF TMR1IF 0000 0000 0000 0000
OSFIE TMR2IE TMR1IE 0000 0000 0000 0000
8Ch
PIE1
9Ah
EEDAT
EEADR
EECON1
EECON2
EEDAT7 EEDAT6 EEDAT5 EEDAT4 EEDAT3 EEDAT2 EEDAT1 EEDAT0 0000 0000 0000 0000
EEADR7 EEADR6 EEADR5 EEADR EEADR EEADR EEADR EEADR 0000 0000 0000 0000
9Bh
9Ch
—
—
—
—
WRERR WREN
WR
RD
---- x000 ---- q000
---- ---- ---- ----
(1)
9Dh
EEPROM Control register 2
Legend:
x= unknown, u= unchanged, — = unimplemented read as ‘0’, q= value depends upon condition.
Shaded cells are not used by data EEPROM module.
Note 1: EECON2 is not a physical register.
DS41202C-page 74
Preliminary
2004 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
