During 1999, I did a Microcontroller course. LA51 was written so that I could compile A51 programs within the comforts of a bash shell environment. It's not perfect, but it has served me well (and I still use it to this day -- May 2007).

LA51 is very simple-- It will convert an A51 assembly language program:

start_address = 8000h

  org   start_address
start:  
  mov   p1,#0ffh
loop:
  mov  c,090h
  cpl  c
  mov  0f8h,c
  mov  c,093h
  mov  0fbh,c
  ljmp loop
  end

into Intel HEX:

:0F8000007590FFA290B392F8A29392FB028003B7
:00000001FF