//Seiko RTC chip uses an annoying packing system where the LSB
// of the BCD represented data is in the MSB of the value
// that has to be written to the register.  This function
// does the bitwise flip of each nybble using a lookup, and
// swaps the two nybbles. 
unsigned char RTC_ConvertRBCD( unsigned char value ) {
    const unsigned char tobcd[] = { 0x0, 0x8, 0x4, 0xC,
      0x2, 0xA, 0x6, 0xE, 0x1, 0x9, 0x5, 0xD, 0x3, 0xB,
      0x7, 0xF };

    return (tobcd[value & 0x0F] << 4 ) + tobcd[value >> 4];
}

//Input is a 8bit number, returns the BCD encoded, bit reversed
// value needed by the Seiko RTC chip registers
unsigned char RTC_ToRTCBCD( unsigned char value ) {
    return RTC_ConvertRBCD( ( ( value / 10) << 4) + ( value % 10 ) );
    //return  RTC_ConvertRBCD( ( ( value / 10) << 4) + ( value & 0x0F) );
}

//Input is a bit reversed packed BCD register value from
// the Seiko RTC chip, return is a normal 8bit value
unsigned char RTC_FromRTCBCD( unsigned char bcdvalue ) {
    unsigned char unpacked = RTC_ConvertRBCD( bcdvalue );
    return ( ( unpacked >> 4 ) * 10) + ( unpacked & 0x0F );
}


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