Datasheet

ManualsBrandsMICROCHIP TECHNOLOGY ManualsMicrocontrollers, Microprocessors & QuartzesEmbedded microcontroller SSOP 20 8-Bit 20 MHz I/O number 11

100

PIC12F635/PIC16F636/639

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 of 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 0000 000x

PIR1 EEIF

LVDIF CRIF C2IF

(1)

C1IF OSFIF — TMR1IF 0000 00-0 0000 00-0

PIE1

EEIE LVDIE CRIE C2IE

(1)

C1IE OSFIE —TMR1IE0000 00-0 0000 00-0

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

EEADR EEADR7

(1)

EEADR6 EEADR5 EEADR4 EEADR3 EEADR2 EEADR1 EEADR0 0000 0000 0000 0000

EECON1

— — — — WRERR WREN WR RD ---- x000 ---- q000

EECON2 EEPROM Control Register 2 (not a physical register) ---- ---- ---- ----

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

Shaded cells are not used by the data EEPROM module.

Note 1: PIC16F636/639 only.