Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cbmvax!fred
From: fred@cbmvax.UUCP (Fred Bowen)
Newsgroups: comp.sys.cbm
Subject: Re: TWO CARTRIDGES AT ONCE
Message-ID: <7116@cbmvax.UUCP>
Date: 22 Jun 89 15:38:56 GMT
References: <89061907384920@masnet.uucp> <3028@csd4.milw.wisc.edu> <7107@cbmvax.UUCP> <3041@csd4.milw.wisc.edu>
Reply-To: fred@cbmvax.UUCP (Fred Bowen)
Organization: Commodore Technology, West Chester, PA
Lines: 44

In article <3041@csd4.milw.wisc.edu> Joe Greco writes:
>In comp.sys.cbm article <7107@cbmvax.UUCP> Fred Bowen wrote:
>
>] I trust you have modified the 1700/1750 C128-compatible REUs to work properly
>] on your C64.
>
>I've never HAD any problems running 128 REU's on my machines.  You
>know the saying, if it isn't broke- don't fix it!

	This is not a will work / won't work thing- there are
	really close timing factors involved.  It also depends
	upon the vintage of your C64.

> [...] But: There *IS* no additional TTL delay, if you understand how
>my decoding works.  IO1 and IO2 go through two 74LS139 decoders, my
>new IO blocks also do.  The circuitry and timing are identical, with
>the possible exception of a one foot ribbon cable I introduced into
>the works.  That isn't it, as ONE REU works all by itself.

	Right you are- I apologize for not looking more closely.
	The ribbon cable is still a bad idea timing-wise.  Although
	I'm sure what the situation is, you have not made things
	clear:  When both REUs are connected, do they both fail to work?
	If not, which one works?  When only one REU is connected to the
	ribbon cable, does it work?  Just for the heck of it, try 'em
	without the ribbon cable, and without the resistor at R4.

>But, still, did you run two REU's or were you just relocating ONE?
>That is the $1,000,000.00 question.

	Gee, the price keeps going up :-)   Okay- I have both REUs
	connected and functioning properly (pay up :-).  Perhaps your
	C64 is old enough that you are hosed.  Perhaps there is some
	loading problem hanging all that stuff off the dot clock.

	Perhaps I'm out of ideas.  I suggest we continue this discussion
	via email.

-- 
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