PIC12F635ESS datasheet(96/234 Pages) MICROCHIP

96 / 234 page

PIC12F635/PIC16F636/639

DS41232D-page 94

9.5

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 (nominal 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

9.6

Data EEPROM Operation During

Code Protection

Data memory can be code-protected by programming

the CPD bit in the Configuration Word (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 9-1:

SUMMARY OF REGISTERS ASSOCIATED WITH DATA EEPROM

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 000x

PIR1

EEIF

LVDIF

CRIF

C2IF(1)

C1IF

OSFIF

—

TMR1IF

0000 00-0

PIE1

EEIE

LVDIE

CRIE

C2IE(1)

C1IE

OSFIE

—TMR1IE

0000 00-0

EEDAT

EEDAT7

EEDAT6

EEDAT5

EEDAT4

EEDAT3

EEDAT2

EEDAT1

EEDAT0

0000 0000

EEADR

EEADR7(1)

EEADR6

EEADR5

EEADR4

EEADR3

EEADR2

EEADR1

EEADR0

0000 0000

EECON1

—

WRERR

WREN

---- x000

---- q000

EECON2

EEPROM Control Register 2 (not a physical register)

---- ----

Legend:

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

Shaded cells are not used by the data EEPROM module.

Note

PIC16F636/639 only.

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