PIC16F877ATISLASHML datasheet(41/234 Pages) MICROCHIP

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 2003 Microchip Technology Inc.

DS39582B-page 39

PIC16F87XA

3.7

Protection Against Spurious Write

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.

3.8

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 microcon-

troller can read and write to program memory normally,

as well as execute instructions. Writes by the device may

be selectively inhibited to regions of the memory depend-

ing on the setting of bits WR1:WR0 of the configuration

word (see Section 14.1 “Configuration Bits” for addi-

tional 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

xxxx xxxx

---0 q000

10Fh

EEADRH

—

EEPROM/Flash Address Register High Byte

xxxx xxxx

---- ----

18Ch

EECON1

EEPGD

—

WRERR

WREN

x--- x000

---0 q000

18Dh

EECON2

EEPROM Control Register 2 (not a physical register)

---- ----

0Dh

PIR2

—

CMIF

—EEIF

BCLIF

—

CCP2IF

-0-0 0--0

8Dh

PIE2

—

CMIE

—EEIE

BCLIE

—

CCP2IE

-0-0 0--0

Legend:

= unknown, u = unchanged, - = unimplemented, read as ‘0’, q = value depends upon condition.

Shaded cells are not used by data EEPROM or Flash program memory.

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