gistfile1.txt

//rom user id addresses
#define ROM_ROW_SIZE            32
#define ROM_ID                  0x8000
#define ROM_ID0                 0x8000
#define ROM_ID1                 0x8001
#define ROM_ID2                 0x8002
#define ROM_ID3                 0x8003
#define ROM_MY_ADDRESS          ROM_ID0

/*------------------------------------------------------------------------------
 - read byte from flash, config, or eeprom
 - flash 0x0000-FLASH_SIZE, config 0x8000+, eeprom 0xF000-0xF0FF
 - return 16bit read value (only 14bits of flash, upper 2 bits are 0)
 - eeprom read returns 16bits, but only 8bits valid (upper 8 should be 0)
------------------------------------------------------------------------------*/  
uint16_t rom_read( uint16_t waddr )
{
    NVMADRH = waddr>>8;             //set address
    NVMADRL = waddr;
    NVMREGS = 0;                    //assume flash space
    if( waddr & 0x8000 ) NVMREGS = 1;//else config space if waddr bit15 set
    RD = 1;                         //start read
    NVMREGS = 0;
    return NVMDATH<<8 | NVMDATL;
}

/*------------------------------------------------------------------------------
 - unlock sequence for nvm
 - irq's off while writing
------------------------------------------------------------------------------*/ 
void rom_unlock()
{
    while( WR == 1 );               //in case eeprom still writing
    //unlock
    uint8_t gie_save = GIE;         //save irq status
    GIE = 0;                        //irq off
    WREN = 1;                       //program/erase enable
    NVMCON2 = 0x55;                 //unlock
    NVMCON2 = 0xAA;
    WR = 1;                         //write
    //cpu stops here
    WREN = 0;                       //program/erase disable        
    if( gie_save ) GIE = 1;         //restore irq status
    //done
}

/*------------------------------------------------------------------------------
 - write word to flash, user id, or eeprom
 - if address >= 0x8000 user id space, if >= 0xF000 eeprom
 - if flash or user id, assumes row erase is already done
------------------------------------------------------------------------------*/
void rom_write_word( uint16_t waddr, uint16_t wdata )
{
    NVMADRH = waddr>>8;             //set address
    NVMADRL = waddr;
    NVMDATH = wdata>>8;             //and data
    NVMDATL = wdata;
    if( waddr & 0x8000 ) NVMREGS = 1;//config/eeprom space
    rom_unlock();
    NVMREGS = 0;
}

/*------------------------------------------------------------------------------
 - erase rom row
 - irq's off while writing
------------------------------------------------------------------------------*/ 
void rom_erase_row( uint16_t waddr )
{
    FREE = 1;                       //erase flag (is only set in this function)
    rom_write_word( waddr, 0 );
    FREE = 0;                       //leave everything as before
}

/*------------------------------------------------------------------------------
 - write data to latch
------------------------------------------------------------------------------*/
void rom_write_latch( uint16_t waddr, uint16_t wdata )
{
    LWLO = 1;                       //load word to latch only
    rom_write_word( waddr, wdata );
    LWLO = 0;                       //leave everything as before
}

/*------------------------------------------------------------------------------
 - write to user id location addr (0x8000-0x8003)
 - preserve other id locations in this row
------------------------------------------------------------------------------*/
void rom_write_id( uint16_t addr, uint16_t wdat )
{
    //return if invalid address
    if( addr < ROM_ID0 || addr > ROM_ID3 ) return;
    //preserve other id's directly into latches
    for( uint16_t i = ROM_ID0; i <= ROM_ID3; i++ ){
        if( i == addr ) continue; //skip writing to latch for our target addr
        rom_write_latch( i, rom_read( i ) );
    }
    //erase row (latches not affected by erase)
    rom_erase_row( ROM_ID );
    //now write our new address data, programming the whole row from latches
    rom_write_word( addr, wdat );   
}