from 0-9 hex and decimal are exactly the same so no "conversion" is required. The high nibble is really decoding the device since you need a pin for each device so you want binary 0001, 0010, 0100, 1000. This is hex 1,2,4,8. It is simplest to treat the byte as 2 nibbles, the low one with the number to display, the other with the address.