Writing EEPROM on PIC18F27Q83

Question

I'm trying to write the EEPROM (DFM) on a PIC18F27Q83. I copied the sequence from the datasheet exactly and it still fails. The device id is 0x9909 and revision id is 0xA45.

        // Save interrupt enable bit value
    unsigned char GIEBitValue = INTCON0bits.GIE;
        // Load NVMADR with the target address of the byte
    NVMADR = 0x380000;
    NVMDATL = outgoing_data.data_bytes[0]; // Load NVMDAT with the desired value
    NVMCON1bits.CMD = 0x04; // Set the byte write command and post increment
    INTCON0bits.GIE = 0; // Disable interrupts
        //????????? Required Unlock Sequence ?????????
    NVMLOCK = 0x55;
    NVMLOCK = 0xAA;
    NVMCON0bits.GO = 1; // Start byte write
        //???????????????????????????????????????????????
    while (NVMCON0bits.GO); // Wait for the write operation to complete
        // Verify byte write operation success and call the recovery function if needed
    if (NVMCON1bits.WRERR)
    {
        INTCON0bits.GIE = GIEBitValue; // Restore interrupt enable bit value
        NVMCON1bits.CMD = 0;
        return false;
    }

After the GO bit goes to zero meaning the operation has completed the WRERR bit stays at 1 meaning the operation failed. I have watched the WRERR bit and it is just 1 all the time. I assume that once a successful write occurs it should go to zero.

The chip is running on a 10MHz external oscillator and OFSC is 40MHz. All of that has been verified and I have UART comms with the chip no problem.

Data Sheet

Answer 1

Your write sequence looks similar to what the datasheet proposes:

// Code sequence to write one byte to a DFM
// DFM target address is specified by DFM_ADDR
// Target data are specified by ByteValue

// Save interrupt enable bit value
uint8_t GIEBitValue = INTCON0bits.GIE;
// Load NVMADR with the target address of the byte
NVMADR = DFM_ADDR;
NVMDATL = ByteValue; // Load NVMDAT with the desired value
NVMCON1bits.CMD = 0x03; // Set the byte write command
INTCON0bits.GIE = 0; // Disable interrupts
//––––––––– Required Unlock Sequence –––––––––
NVMLOCK = 0x55;
NVMLOCK = 0xAA;
NVMCON0bits.GO = 1; // Start byte write
//–––––––––––––––––––––––––––––––––––––––––––––––
INTCON0bits.GIE = GIEBitValue; // Restore interrupt enable bit value (if interrupts are desired during DFM write)
while (NVMCON0bits.GO); // Wait for the write operation to complete

// Verify byte write operation success and call the recovery function if needed
if (NVMCON1bits.WRERR){
    WRITE_FAULT_RECOVERY();
}

NVMCON1bits.CMD = 0; // Disable writes to memory

The reasons for WRERR to be asserted are:

1. A write operation was interrupted by a Reset,
2. or a write or erase operation was attempted on a write-protected area,
3. or a write or erase operation was attempted on an unimplemented area,
4. or a write or erase operation was attempted while locked,
5. or a page operation was directed to a DFM area

Reason 1 isn't the probable cause, and reasons 3, 4 and 5 can be ruled out.

The most likely reason is that the Data EEPROM is write-protected.

Check the CONFIG8 register to exclude or confirm this possibility: