PIC16F87 Datasheet, PDF (36/214 Pages) Microchip Technology – 18/20/28-Pin Enhanced FLASH Microcontrollers with nanoWatt Technology

PIC16F87/88
3.8 Protection Against Spurious Write
There are conditions when the device should not write
to the data EEPROM memory. To protect against spu-
rious EEPROM 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.
3.9 Operation During Code Protect
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
disabled. 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 WRT1:WRT0
of the configuration word (see Section 15.1 “Configu-
ration Bits” for additional information). External
access to the memory is also disabled.
TABLE 3-1: REGISTERS/BITS ASSOCIATED WITH DATA EEPROM AND
FLASH PROGRAM MEMORIES
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
10Ch EEDATA EEPROM/FLASH Data Register Low Byte
xxxx xxxx uuuu uuuu
10Dh EEADR EEPROM/FLASH Address Register Low Byte
xxxx xxxx uuuu uuuu
10Eh EEDATH —
— EEPROM/FLASH Data Register High Byte
--xx xxxx --uu uuuu
10Fh EEADRH —
—
—
—
— EEPROM/FLASH Address
---- -xxx ---- -uuu
Register High Byte
18Ch EECON1 EEPGD —
—
FREE WRERR WREN
WR
RD x--x x000 x--x q000
18Dh EECON2 EEPROM Control Register 2 (not a physical register)
---- ---- ---- ----
0Dh
PIR2
OSFIF CMIF
—
EEIF
—
—
—
— 00-0 ---- 00-0 ----
8Dh
PIE2
OSFIE CMIE
—
EEIE
—
—
—
— 00-0 ---- 00-0 ----
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.
DS30487B-page 34
Preliminary
 2003 Microchip Technology Inc.