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From: cdl@mplvax.UUCP (Carl Lowenstein)
Newsgroups: net.lang.c
Subject: Re: PDP-11 as 68000 Cloner
Message-ID: <246@mplvax.UUCP>
Date: Thu, 5-Dec-85 16:01:26 EST
Article-I.D.: mplvax.246
Posted: Thu Dec  5 16:01:26 1985
Date-Received: Sat, 7-Dec-85 04:29:42 EST
References: <3418@brl-tgr.ARPA>
Reply-To: cdl@mplvax.UUCP (Carl Lowenstein)
Organization: Marine Physical Laborator of SIO at UCSD
Lines: 31

In article <3418@brl-tgr.ARPA> cottrell@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@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
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