PIC16F684 datasheet(80/192 Pages) MICROCHIP

80 / 192 page

PIC16F684

DS41202F-page 78

10.5

Protection Against Spurious Write

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

Power-up

Timer

(64 ms

duration)

prevents

EEPROM write.

The write initiate sequence and the WREN bit together

help prevent an accidental write during:

• Brown-out

•Power Glitch

• Software Malfunction

10.6

Data EEPROM Operation During

Code-Protect

Data memory can be code-protected by programming

the CPD bit in the Configuration Word register

(Register 12-1) to ‘0’.

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

data

memory.

Programming unused locations in program memory to

‘0’ will also help prevent data memory code protection

from becoming breached.

TABLE 10-1:

SUMMARY OF ASSOCIATED DATA EEPROM REGISTERS

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Value on:

POR, BOR

Value on

all other

Resets

INTCON

GIE

PEIE

T0IE

INTE

RAIE

T0IF

INTF

RAIF

0000 0000

PIR1

EEIF

ADIF

CCP1IF

C2IF

C1IF

OSFIF

TMR2IF

TMR1IF

0000 0000

PIE1

EEIE

ADIE

CCP1IE

C2IE

C1IE

OSFIE

TMR2IE

TMR1IE

0000 0000

EEDAT

EEDAT7

EEDAT6

EEDAT5

EEDAT4

EEDAT3

EEDAT2

EEDAT1

EEDAT0

0000 0000

EEADR

EEADR7

EEADR6

EEADR5

EEADR4 EEADR3 EEADR2 EEADR1 EEADR0

0000 0000

EECON1

—

WRERR

WREN

---- x000

---- q000

EECON2(1) EEPROM Control Register 2

---- ----

Legend:

= unknown, u = unchanged, – = unimplemented read as ‘0’, q = value depends upon condition. Shaded cells are not used by the Data

EEPROM module.

Note

EECON2 is not a physical register.

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