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From: fred@cbmvax.UUCP (Fred Bowen)
Newsgroups: comp.sys.cbm
Subject: Re: 1764 RAM expansion
Message-ID: <2439@cbmvax.UUCP>
Date: Thu, 1-Oct-87 13:37:57 EDT
Article-I.D.: cbmvax.2439
Posted: Thu Oct  1 13:37:57 1987
Date-Received: Mon, 5-Oct-87 07:34:29 EDT
References: <1791@sputnik.COM> <2359@cbmvax.UUCP>
Organization: Commodore Technology, West Chester, PA
Lines: 31

> Speaking of the 1764 Ram expander, can the 128 use the RAM it it while
> in 64 mode?  Can it access it in 128 mode?   What about in CP/M mode?
> Can it be a substituted for the 128's RAM expansion or is the DMA chip
> different???
> For that matter, if they are different, can a good techie wire in both
> expanders on a 128 for more then 640k?

The boards for the 17xx RAM expanders are basically the same, except for one
resistor and, of course, the amount of RAM.  There were several different
layouts of the PCB, the most noticeable difference being the packaging of
the DMA controller (8726), DIP vs. quad pack.

A good techie could, indeed, modify a 1764 for use on a C128.  All you gotta
do is add one 390 ohm resistor at location R4.  This is necessary to tweek
the relationship of the dot clock to phi-2, which differs slightly between
C64 and C128's.

Once you have either a 1700 modified as above, or a 1700/1750, you can use
it in any of the 3 modes of the C128: 64, 128, or CP/M.  CP/M makes good
use of it as a RAM disk- simply address as device M:.   In native C128
mode, BASIC provides 3 commands (FETCH,STASH, and SWAP) specifically for
talking to the DMA controller.  The upgrade 128 ROMs enhance this further
by allowing full access to all internal banks of memory.

--
-- 
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