PIC16F87XA
3.7
Protection Against Spurious Write
3.8
Operation During Code Protect
There are conditions when the device should not write
to the data EEPROM or FLASH program memory. To
protect against spurious writes, various mechanisms
have been built-in. On power-up, WREN is cleared.
Also, the Power-up Timer (72 ms duration) prevents an
EEPROM write.
The write initiate sequence and the WREN bit together
help prevent an accidental write during brown-out,
power glitch, or software malfunction.
When the data EEPROM is code protected, the micro-
controller can read and write to the EEPROM normally.
However, all external access to the EEPROM is dis-
abled. External write access to the program memory is
also disabled.
When program memory is code protected, the micro-
controller can read and write to program memory nor-
mally, as well as execute instructions. Writes by the
device may be selectively inhibited to regions of the
memory, depending on the setting of bits WR1:WR0 of
the configuration word (see Section 14.1 for additional
information). External access to the memory is also
disabled.
TABLE 3-1:
REGISTERS/BITS ASSOCIATED WITH DATA EEPROM
AND FLASH PROGRAM MEMORIES
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
Address
10Ch
10Dh
10Eh
10Fh
18Ch
18Dh
0Dh
8Dh
EEDATA
EEADR
EEDATH
EEADRH
EECON1
EECON2
PIR2
PIE2
EEPROM/FLASH Data Register Low Byte
EEPROM/FLASH Address Register Low Byte
—
—
EEPGD
—
—
—
EEPROM/FLASH Data Register High Byte
—
—
EEPROM/FLASH Address Register High Byte
—
WRERR
WREN
WR
RD
xxxx xxxx uuuu uuuu
xxxx xxxx uuuu uuuu
xxxx xxxx ---0 q000
xxxx xxxx ---- ----
x--- x000 ---0 q000
---- ---- ---- ----
EEPROM Control Register2 (not a physical register)
—
—
CMIF
CMIE
—
—
EEIF
EEIE
BCLIF
BCLIE
—
—
—
—
CCP2IF
CCP2IE
-0-0 0--0 -0-0 0--0
-0-0 0--0 -0-0 0--0
Legend:
x
= unknown,
u
= unchanged,
-
= unimplemented, read as '0',
q
= value depends upon condition.
Shaded cells are not used by Data EEPROM or FLASH Program Memory.
2001 Microchip Technology Inc.
Advance Information
DS39582A-page 37
MICROCHIP [ MICROCHIP TECHNOLOGY ]
