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Path: utzoo!watmath!clyde!rutgers!cbmvax!hedley
From: hedley@cbmvax.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: expanding amiga 1000 to 2000
Message-ID: <1430@cbmvax.cbmvax.cbm.UUCP>
Date: Wed, 18-Feb-87 12:39:32 EST
Article-I.D.: cbmvax.1430
Posted: Wed Feb 18 12:39:32 1987
Date-Received: Thu, 19-Feb-87 20:28:29 EST
References: <12279780357.24.PKG.SPARKMAN@MCC.COM>
Reply-To: hedley@cbmvax.UUCP (Hedley Davis)
Organization: Commodore Technology, West Chester, PA
Lines: 73

In article <12279780357.24.PKG.SPARKMAN@MCC.COM> PKG.SPARKMAN@MCC.COM (Aubrey Sparkman) writes:
>
>As far as the power requirements goes, it seems that one could (In line with
>the daughter board idea) remove the 256K plug in module from the front of
>the amiga 1000, remove the 256K dram chips from the mother board, and use
>1 meg dram chips to get 2 meg chip ram without changeing chip count.
>Yes I know the 1 meg chips are more expensive, but then you don't have to add
>a power supply (do you?) and it is simpler.
>

All RAM is not created equal.

I'm sure both of you have heard of "CHIP memory" and "FAST memory".
"FAST" memory is memory that sits on the 68000 buss. It is not
accessable by the custom chips. Its called "FAST" because the custom
chips cannot lock the processor out of accesses to that memory.
Therefore, even if the custom chips a blitting, and DMAing and just
wreaking havoc on their buss, the processor can still purr along quite
nicely.

"CHIP" memory is accessable both by the processor, and the custom chips.
This means, that under certain conditions (Hold and Modify mode for
example ), the custom chips can prevent the processor from using this 
memory from time to time. Hence, code running out of this memory may
execute slower because the processor cannot do as much work.

The custom chips not only afford the amiga many capabilties in terms of
graphics, and sound, but they also perform simple tasks like generating
signals like RAS and CAS, and multiplexed addresses. These are required
to use DRAMS which are currently the least expensive memory technology.
In short, the custom chips provide what would otherwise be an expensive
DRAM interface. Unfortunately, they only do this for CHIP memory.

Both the 256K internal, and the 256K expansion memory on the A1000 are
CHIP memory. Inside the A1000, none of the signals exsist to directly
drive FAST memory. Therefore, to add FAST memory, the cost would be
considerably higher. ( Read: considerably more complex ).

Therefore, adding memory space to the A1000 by simply changing the
DRAMs, and maybe running a couple of jumpers, is doomed to only being
able to add CHIP memory space. The bad news is that the custom chips 
in the A1000 only have sufficient pins to address 512K. Therefore,
if you already have 512K, its full. No more room. No Vacancy.      

You can of course add FAST memory to the A1000, but this requires a full
and complete 68000<->DRAM interface including some sort of refresh, and
other goodies. Because you have no sockets, you therefore need a new
PCB. Further the A1000 expansion architecture requires a protocul called
AUTOCONFIG which is the method by which the A1000 recognizes expansion
boards, identifies them, and if they are memory, adds them to the system
memory free list. This is not too awful difficult, but it is certainly
not trivial, and therefore is beyond the reach of your average Amiga
owner. If you are really interested in persueing this approach, and
building your own board with lots of chips, I suggest you contact AMIGA
developer's support. From there, you can obtain a copy ( at a nominal
cost ) of the Amiga Schematics and Expansion Specifications manual.
Please do not expect these people to "hold you hand" and walk you
through every minute detail of the operation. They are extremely busy,
supporting a large host of proffesional software developers. They are
not really hardware hacks. You are warned that unless you are a good
engineer, you may be in for a rough time.

On the other hand, you could save an enourmous amount of time and energy
by simply purchasing something that you know works from the many
hardware companies supplying expansion memory for the A1000. This is
not a sales pitch, it is simply good advice.  


Hedley    


Any effort to add memory space to CHIP memoryC
This means, under certain conditions ( Hold and Moe