This small, and common, gem converts a hexadecimal number into a ASCII value that is possible to put in a string. Since Norbert Juffa brougt the gem to my attention, therefor he will be credited here. He also provided the nice comments.

;
; input:
;   al = single hex digit
;
; output:
;   al = single ASCII digit
;
; destroys:
;   flags
;

        cmp     al,10           ; if x < 10, set CF = 1
        sbb     al,69h          ; 0-9: 96h .. 9Fh,  A-F: A1h..A6h
        das                     ; 0-9: subtr. 66h -> 30h-39h,
                                ; A-F: subtr. 60h -> 41h..46h