z80 Assembly: Binary-Coded Decimal

One method for displaying numbers larger than 16 bits is to convert it to Binary Coded Decimal (BCD) first, and display the result. BCD works by using four bits to store each decimal (base 10) digit of a number. The following code can convert a number to BCD, and display it. It’s currently written to convert a 24 bit number to a 10 digit BCD number, but can be modified to support anything really. It is memory ineffecient, because it uses one byte for each digit rather than storing two digits per byte. This is useful though because it makes the display routine simpler.