PDP-11 as 68000 Cloner

[Carl Lowenstein]

In article <3418 at brl-tgr.ARPA> cottrell at nbs-vms.arpa (COTTRELL, JAMES) writes:
>/*  >> = Me, > = Ron Natalie
>> > Of course there are *some* differences. And of course the 68000 is a 
>> > 32-bit machine (crammed onto a 16-bit bus) while the pdp is a 16-bit one.
>> 
>> And it has the bytes in the wrong order.
>
>Great! Another Little Endian!
> 
>> > As far as relative code, the pdp is missing something. How do you
>> > load the address of a variable relative to the PC? This way:
>> > 
>> > 		mov	pc,r0			; address of `here'
>> > 	here:	add	#foobar-here,r0		; make relative
>> > 
>> Bad example, now what are you going to do with this loaded
>> address?
>
>Bad example, now what can I do with that loaded question? You see,
>foobar just happens to be an array! What I need to do is get it's
>address into a register so I can auto-{in,de}crement the bugger.
>
>	jim		cottrell at nbs
>*/
The most likely thing I would do with that loaded register is send
the value off to some external hardware, like a DMA controller,
which needs to know absolute addresses.

-- 
	carl lowenstein		marine physical lab	u.c. san diego
	{ihnp4|decvax|akgua|dcdwest|ucbvax}	!sdcsvax!mplvax!cdl