PIC16F87 datasheet(10/24 Pages) MICROCHIP

10 / 24 page

PIC16F87/88

DS39607B-page 10

 2002 Microchip Technology Inc.

3.5

Erasing Program and Data

Memory

Depending on the state of the code protection bits,

program and data memory will be erased using

different methods. The first two commands are used

when both program and data memories are not code

protected. The third command is used when either

memory is code protected, or if you want to also erase

the code protect bits. A device programmer should

determine the state of the code protection bits and then

apply the proper command to erase the desired

memory.

3.5.1

ERASING PROGRAM AND

DATA MEMORY

When both program and data memories are not code-

protected, they can be individually erased by the

following ‘Bulk Erase’ commands. If it is desired to

erase both program and data memory with a single

command, the ‘Chip Erase’ command must be used

whether code protection is disabled or enabled

(detailed in Section 3.5.1.3 “Chip Erase”).

3.5.1.1

Bulk Erase Program Memory

When this command is performed, and is followed by

a ‘Begin Erase’ command, the entire program memory

will be erased.

If the address is pointing to user memory, only the user

memory will be erased.

If the address is pointing to the configuration memory

(2000h-2008h), then both the user memory and the

configuration memory will be erased. The configuration

words will not be erased, even if the address is pointing

to location 2007h.

Previously, a load data with 0FFh command was

recommended before any ‘Bulk Erase’. On these

devices, this will not be required.

The ‘Bulk Erase’ command is disabled when the CP

bit is programmed to ‘0’, enabling code-protect.

A timing diagram for this command is shown in

Figure 7-8.

3.5.1.2

Bulk Erase Data Memory

When this command is performed, and is followed by

a ‘Begin Erase’ command, the entire data memory will

be erased.

The ‘Bulk Erase Data’ command is disabled when the

CPD bit is programmed to ‘0’, enabling protected data

memory. A timing diagram for this command is shown

in Figure 7-9.

3.5.1.3

Chip Erase

This command, when performed, will erase the

program memory, EE data memory, and all of the code

protection bits. All on-chip Flash and EEPROM

memory is erased, regardless of the address contained

in the PC.

When a Chip Erase command is issued and the PC

points to (0000h-1FFFh), the configuration words

(2007h and 2008h) and the user program memory will

be erased. When a Chip Erase command is issued and

the PC points to (2000h-2008h), all of the configuration

memory, program memory, and data memory will be

erased.

The Chip Erase is internally self-timed to ensure that all

program and data memory are erased before the code

protect bits are erased. A timing diagram for this

command is shown in Figure 7-10.

3.5.2

ERASING CODE-PROTECTED

MEMORY

For the PIC16F87/88 devices, once code protection is

enabled, all protected program and data memory

locations read all '0's and further programming is

disabled. The ID locations and configuration words

read out unscrambled and can be reprogrammed

normally. The only command to erase a code-protected

PIC16F87/88 device is the ‘Chip Erase’. This erases

program memory, data memory, configuration bits and

ID locations, as described in Section 3.5.1.3 “Chip

Erase”. Since all data within the program and data

memory will be erased when this command is

executed, the security of the data or code is not

compromised.

Note:

All ‘Bulk Erase’ operations must take place

at the 4.5V to 5.5V VDD range.

Note:

The Chip Erase operation must take place

at the 4.5V to 5.5V VDD range.

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