Here's a code snippet.
Hope it helps.

figure out the rest. It should not be too hard. :)

BTW: Don Knuth has some prime information in his book about radix conversion.

; ==========================================================
; binasc
; binasc takes the contents of the accumulator and converts it
; into two ascii hex numbers. the result is returned in the
; accumulator and r2.
; ==========================================================
;
binasc: mov r2, a ; save in r2
anl a, #0fh ; convert least sig digit.
add a, #0f6h ; adjust it
jnc noadj1 ; if a-f then readjust
add a, #07h
noadj1: add a, #3ah ; make ascii

xch a, r2 ; put result in reg 2
swap a ; convert most sig digit
anl a, #0fh ; look at least sig half of acc
add a, #0f6h ; adjust it
jnc noadj2 ; if a-f then re-adjust
add a, #07h
noadj2: add a, #3ah ; make ascii
ret