PIC16F87X datasheet(46/200 Pages) MICROCHIP

46 / 200 page

PIC16F87X

DS30292A-page 46

Preliminary

4.7

Write Verify

Depending on the application, good programming

practice may dictate that the value written to the mem-

ory should be veriﬁed against the original value. This

should be used in applications where excessive writes

can stress bits near the speciﬁcation limit.

Generally a write failure will be a bit which was written

as a '1', but reads back as a '0' (due to leakage off the

bit).

4.8

Protection Against Spurious Write

4.8.1

EEPROM DATA MEMORY

There are conditions when the device 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, the WREN bit 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.

4.8.2

PROGRAM FLASH MEMORY

To protect against spurious writes to FLASH program

memory, the WRT bit in the conﬁguration word may be

programmed to ‘0’ to prevent writes. WRT and the con-

ﬁguration word cannot be programmed by user code,

only through the use of an external programmer.

4.9

Operation during Code Protect

Each reprogrammable memory block has its own code

protect mechanism. External Read and Write opera-

tions are disabled if either of these mechanisms are

enabled.

4.9.3

DATA EEPROM MEMORY

The microcontroller itself can both read and write to the

internal Data EEPROM regardless of the state of the

code protect conﬁguration bit.

4.9.4

PROGRAM FLASH MEMORY

The microcontroller can read and execute instructions

out of the internal FLASH program memory regardless

of the state of the code protect conﬁguration bits. How-

ever the WRT conﬁguration bit and the code protect bits

have different effects on writing to program memory.

Table 7-1 shows the various conﬁgurations and status

of reads and writes. To erase the WRT or code protec-

tion bits in the conﬁguration word requires that the

device be fully erased.

TABLE 7-1:

READ/WRITE STATE OF INTERNAL FLASH PROGRAM MEMORY

Conﬁguration Bits

Memory Location

Internal

Read

Internal

Write

ICSP Read

ICSP Write

CP1

CP0

WRT

All program memory

Yes

Unprotected areas

Yes

Protected areas

Yes

Unprotected areas

Yes

Protected areas

Yes

Unprotected areas

Yes

Protected areas

Yes

Unprotected areas

Yes

Protected areas

Yes

All program memory

Yes

All program memory

Yes

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