Microchip Technology MA240017 Data Sheet

DS39927C-page 54

 2008-2011 Microchip Technology Inc.

6.4.1

ERASE DATA EEPROM

The data EEPROM can be fully erased, or can be
partially erased, at three different sizes: one word, four
words or eight words. The bits, NVMOP<1:0>
(NVMCON<1:0>), decide the number of words to be
erased. To erase partially from the data EEPROM, the
following sequence must be followed:
1.

Configure NVMCON to erase the required
number of words: one, four or eight.

2.

Load TBLPAG and WREG with the EEPROM
address to be erased.

3.

Clear NVMIF status bit and enable NVM
interrupt (optional).

4.

Write the key sequence to NVMKEY.

5.

Set the WR bit to begin erase cycle.

6.

Either poll the WR bit or wait for the NVM
interrupt (NVMIF set).

A typical erase sequence is provided in 

This example shows how to do a one-word erase. Sim-
ilarly, a four-word erase and an eight-word erase can
be done. This example uses ‘C’ library procedures to
manage the Table Pointer (builtin_tblpage and
builtin_tbloffset

) and the Erase Page Pointer

(builtin_tblwtl). The memory unlock sequence
(builtin_write_NVM) also sets the WR bit to initiate
the operation and returns control when complete.

int __attribute__ ((space(eedata))) eeData = 0x1234; // Variable located in EEPROM

 unsigned int offset;

 // Set up NVMCON to erase one word of data EEPROM

 NVMCON = 0x4058;

 // Set up a pointer to the EEPROM location to be erased

 TBLPAG = __builtin_tblpage(&eeData);

// Initialize EE Data page pointer

 offset = __builtin_tbloffset(&eeData);

// Initizlize lower word of address

 __builtin_tblwtl(offset, 0);

// Write EEPROM data to write latch

 asm volatile ("disi #5");

// Disable Interrupts For 5 Instructions

__builtin_write_NVM();

// Issue Unlock Sequence & Start Write Cycle