Binary coded decimal

Binary coded decimal (BCD) uses four bits holding the values 0-9 to represent each digit of a decimal value. Each byte can hold two decimal digits. The protocol uses the value 0xFF to indicate that some values are unlimited.

BCD		Decimal
Hex	Dec	Hex	Dec
0x00	0	0x00	0
0x09	9	0x09	9
0x10	16	0x0A	10
0x16	22	0x10	16
0x99	153	0x63	99
0xFF	255	Unlimited

Here is an example of how to convert to and from binary coded decimal.

byte ToDecimal(byte bcd)
{
	if (bcd == 0xff) return bcd;
	return (((bcd >> 4) & 0xf) * 10) + (bcd & 0xf);
}

byte ToBinaryCodedDecimal(byte dec)
{
	if (dec == 0xff) return dec;
	return (byte)(((dec / 10) << 4) | (dec % 10));
}