PIC16F818-ESLASHML datasheet(34/176 Pages) MICROCHIP

34 / 176 page

PIC16F818/819

DS39598E-page 32

 2004 Microchip Technology Inc.

3.8

Protection Against Spurious Write

There are conditions when the device should not 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

Power-up

Timer

(72 ms

duration)

prevents

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

normally as well as execute instructions. Writes by the

device may be selectively inhibited to regions of

the memory

depending

the

setting

bits,

WRT1:WRT0,

the

Configuration

Word

(see

Section 12.1

“Configuration

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

18Ch

EECON1 EEPGD

—

FREE

WRERR

WREN

x--x x000

x--x q000

18Dh

EECON2 EEPROM Control Register 2 (not a physical register)

---- ----

0Dh

PIR2

—

EEIF

—

---0 ----

8Dh

PIE2

—

—EEIE

—

---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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