PIC16F15213 datasheet(110/439 Pages) MICROCHIP

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15.1.2.2 NVM Unlock Sequence

The unlock sequence is a mechanism that protects the NVM from unintended self-write programming or erasing.

The sequence must be executed and completed without interruption to successfully complete any of the following

operations:

• PFM Row Erase

• Write of PFM write latches to PFM memory

• Write of PFM write latches to User IDs

• Write to Configuration Words

The unlock sequence consists of the following steps and must be completed in order:

• Write 55h to NVMCON2

• Write AAh to NMVCON2

• Set the WR bit

Once the WR bit is set, the processor will stall internal operations until the operation is complete and then resume

with the next instruction.

Since the unlock sequence must not be interrupted, global interrupts must be disabled prior to the unlock sequence

and re-enabled after the unlock sequence is completed.

Figure 15-2. NVM Unlock Sequence

Filename:

10-000047B.vsd

Title:

FLASH PROGRAM MEMORY UNLOCK SEQUENCE FLOWCHART

Last Edit:

8/24/2015

First Used:

PIC15F1508/9

Note:

Start

Unlock Sequence

End

Unlock Sequence

Write

0x55 to

NVMCON2

Write

0xAA to

NVMCON2

Initiate

Write or Erase operation

(WR = 1)

Rev. 10-000047B

8/24/2015

Example 15-2. NVM Unlock Sequence

NVMCON1bits.WREN = 1;

// Enable write/erase

INTCONbits.GIE = 0;

// Disable global interrupts

// The next three steps are the required unlock sequence

NVMCON2 = 0x55;

// First unlock code

NVMCON2 = 0xAA;

// Second unlock code

NVMCON1bits.WR = 1;

// Initiate write/erase cycle

INTCONbits.GIE = 1;

// Enable global interrupts

NVMCON1bits.WREN = 0;

// Disable further write/erase cycles

PIC16F15213/14/23/24/43/44

NVM - Nonvolatile Memory Control

and its subsidiaries

Data Sheet

DS40002195E-page 110

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