Path: utzoo!attcan!uunet!cbmvax!fred
From: fred@cbmvax.UUCP (Fred Bowen)
Newsgroups: comp.sys.cbm
Subject: Re: Ambitious RAM Expansion Hacking
Keywords: 1700 1750 1764 ram expansion remapping
Message-ID: <5760@cbmvax.UUCP>
Date: 23 Jan 89 16:54:02 GMT
References: <503@csd4.milw.wisc.edu>
Reply-To: fred@cbmvax.UUCP (Fred Bowen)
Organization: Commodore Technology, West Chester, PA
Lines: 31

In article <503@csd4.milw.wisc.edu> jgreco@csd4.milw.wisc.edu (Joe Greco) writes:
>Has anyone managed to run two 1750's on a 64?
>Breaking down the $D000 block isn't hard, it's just a matter of
>pulling thE 74LS239 and adding a second one to decode all 16 256 byte
>pages in the region.  Then use one of the select lines to select the
>"swapping" 1750.

	Probably it would be easier just to select the second REU by hanging
	it off the IO-1 select instead of the IO-2 select.  As long as you
	have enough power and do not "prime" the DMA's in both to respond to
	the $FF00 trigger option simultaneously they should work.  Of course,
	you'd have to provide your own software, since existing software will
	address the REU at $DF00 only.

>My system has a 1750 and MSD IEEE interface.  I used to use the 1750
>for a RAMdisk, but have since needed to use it for data storage
>(swapping).  RAMDOS will not coexist [...]

	The amount of available expansion RAM aside, in the latest TC128
	magazine (is it out yet?) I describe a simple patch to the RAMdisk
	which allows you to "partition" the REU, allocating the lower banks
	for the RAMdisk and leaving the upper banks available for your own
	application.  I also provide a simple patch to BASIC-8 to make it
	compatible with the RAMdisk.
--
-- 
Fred Bowen			uucp:	{uunet|rutgers|pyramid}!cbmvax!fred
				arpa:	cbmvax!fred@uunet.uu.net
				tele:	215 431-9100

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