6502 Shorts - Hex to ASCII. By Lee Davison
[Back]

I know you've all done this before but here's a use for decimal mode. Read on....

The classic way to convert a nibble in A into ASCII is to test if the nibble is greater than nine and, if it is, to add seven before adding the 48 to make the ASCII character.

CMP #$0A ; set carry for +1 if >9 BCC NoAdjust ; branch if <=9 ADC #6 ; adjust if A to F ; (six plus carry = 7!) NoAdjust ADC #"0" ; add ASCII "0"

This is eight bytes long and takes seven or eight cycles depending on the nibble.

Well here's a way that uses decimal mode addition to do that for you.

SED ; set decimal mode CMP #$0A ; set carry for +1 if >9 ADC #"0" ; add ASCII "0" CLD ; clear decimal mode

Six bytes and always nine cycles. Or, if you do a number of nibbles and leave decimal mode set throughout, four bytes and five cycles per digit.

e-mail me