Path: utzoo!attcan!uunet!cbmvax!fred
From: fred@cbmvax.UUCP (Fred Bowen)
Newsgroups: comp.sys.cbm
Subject: Re: 1764 and C-128
Keywords: 1764 in the C-128? Myth or Reality?
Message-ID: <5761@cbmvax.UUCP>
Date: 23 Jan 89 17:14:56 GMT
References: <2413@nunki.usc.edu> <513@csd4.milw.wisc.edu>
Reply-To: fred@cbmvax.UUCP (Fred Bowen)
Organization: Commodore Technology, West Chester, PA
Lines: 37

In article <513@csd4.milw.wisc.edu> jgreco@csd4.milw.wisc.edu (Joe Greco) writes:
>In article <2413@nunki.usc.edu> aliu@nunki.usc.edu (Alejandro Liu) writes:
>>I heard a while back that it is possible to use the 1764 in the C-128,
>>since the 1764 was identical to the 1750 REU except for ONE resistor.
>>Is this true?  Can anybody confirm or deny this?
>
>I've also heard conflicting stories about the configuration of the
>1764's RAM.

Officially, CBM does not recommend using the 1700/1750 expanders on a C64
nor a 1764 expander on a C128.  Many people have done this and report no
problems.  Using any REU on a C64 requires a beefier power supply, which is
included with the 1764.

The only difference among the REU's, aside from the amount of RAM, is a
resistor labeled R4.  Its location depends upon the vintage of the board.
Its purpose is to slightly shift the timing of the dot clock in relation to
other signals on C128's.  This is due to slightly different timing between
the C64 and C128 systems (TTL delays between the expansion port and VIC &
processor chips).

1700's were populated with 2 banks of 64K DRAMs, 1764's with 1 bank of 256K
DRAMs, and 1750's with 2 banks of 256K DRAMs.  I was not aware of any other
configurations.  A rather popular hack is increase the amount of DRAM up to
512K bytes by replacing all the DRAMs in a 1700 with 256K DRAMs (and cutting
jumper J1), or simply adding the second bank of 256K DRAMs to a 1764.  Some
people who have both C64 and C128 systems install a switch and 390 ohm resistor
at location R4, so that they can switch in the resistor for a C128 and switch
it out for a C64.  Usual disclaimer- these hacks void your warranty and are
done entirely at your own risk.
--
-- 
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