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From: fred@cbmvax.UUCP (Fred Bowen)
Newsgroups: comp.sys.cbm
Subject: Re: 1764 RAM Expansion
Message-ID: <2359@cbmvax.UUCP>
Date: Thu, 17-Sep-87 17:14:05 EDT
Article-I.D.: cbmvax.2359
Posted: Thu Sep 17 17:14:05 1987
Date-Received: Sat, 19-Sep-87 15:49:50 EDT
References: <1791@sputnik.COM>
Organization: Commodore Technology, West Chester, PA
Lines: 28

In article <1791@sputnik.COM>, logden@tc.fluke.COM (Leonard Ogden) writes:
> 
> I have another question related to geos. The 1764 RAM Expander, is it just
> memory chips on a board? Or is it more complicated than that?
> 
> What I am really driving at is: can I build one of these puppies at home? 

Yes, it's more complicated than that.  The 17xx RAM expanders are controlled
by a DMA device, which provides both DRAM refresh and the interface to the
host system.  The host's processor does not access the expansion RAM- you
have to program the DMA controller and it will read or write the chunk of
memory you specify.  This sounds complicated, but what it provides in return
is very fast data transfer- much faster than the processor can provide by
addressing each byte.  The DMA controller is a custom IC which, I beleive,
is not generally for sale to the public.  The RAM expanders are reasonably
priced, however, especially for the C64 version which comes with a beefier
power supply necessary for supporting the card.

The more adventuresome techie can probably stuff more RAM (up to 512K- the
DMA controller's limit) onto the board however.

--
-- 
Fred Bowen			uucp:	{ihnp4|rutgers|caip}!cbmvax!fred
				arpa:	beats me
				tele:	215 431-9100

Commodore Electronics, Ltd.,  1200 Wilson Drive,  West Chester,  PA,  19380