Hello Earl,
I compiled using A51.EXE and ran the below code.The results expected (256) were correct (R0=00, R1=01). The code example (UDIV32) provided by Dr. Marshall in the code library section are confirmed correct.
Regards,
Charles Bannister

.org
Start:		
;registers r0-r3 are the dividend and equal 130,560
		mov sp, #0x30
                mov r0, #00h		
		mov r1, #01h
		mov r2, #0FEh
		mov r3, #00h
;register r4 & r5 are the divisor and equal 510
		mov r4, #01h		
		mov r5, #0FEh
		lcall UDIV32
loop:		sjmp loop
UDIV32:  ...
         ...
         ...
.end