PIC16F684 datasheet(76/164 Pages) MICROCHIP

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PIC16F684

DS41202C-page 74

Preliminary

 2004 Microchip Technology Inc.

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:

REGISTERS/BITS ASSOCIATED WITH DATA EEPROM

Address

Name

Bit 7Bit 6Bit 5Bit 4Bit 3Bit 2

Bit 1Bit 0

Value on

POR, BOD

Value on

all other

Resets

0Bh/8Bh

INTCON

GIE

PEIE

T0IE

INTE

RAIE

T0IF

INTF

RAIF

0000 0000 0000 0000

0Ch

PIR1

EEIF

ADIF

CCP1IF

C2IF

C1IF

OSFIF

TMR2IF TMR1IF 0000 0000 0000 0000

8Ch

PIE1

EEIE

ADIE

CCP1IE

C2IE

C1IE

OSFIE

TMR2IE TMR1IE 0000 0000 0000 0000

9Ah

EEDAT

EEDAT7 EEDAT6 EEDAT5 EEDAT4 EEDAT3 EEDAT2 EEDAT1 EEDAT0 0000 0000 0000 0000

9Bh

EEADR

EEADR7 EEADR6 EEADR5 EEADR

EEADR

0000 0000 0000 0000

9Ch

EECON1

—

WRERR

WREN

---- x000 ---- q000

9Dh

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 data EEPROM module.

Note

EECON2 is not a physical register.

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