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From: mikey@bbimg.UUCP
Newsgroups: net.micro.6809
Subject: Re: R.S. floppy controller query
Message-ID: <-1615742@bbimg>
Date: Wed, 2-Jul-86 12:30:00 EDT
Article-I.D.: bbimg.-1615742
Posted: Wed Jul  2 12:30:00 1986
Date-Received: Mon, 7-Jul-86 01:15:33 EDT
References: <1970@osu-eddie.UUCP>
Lines: 27
Nf-ID: #R:osu-eddie.UUCP:1970:bbimg:-1615742:000:1347
Nf-From: bbimg.UUCP!mikey    Jul  2 11:30:00 1986




The problem was that back in the late 70's, when the Model I was first
coming out, Tandy wanted to be able to have 4 drives, the there were only
3 selects.  The line they picked for the 4th select later was defined
as the side select.  They get around the problem in the Model 3/4 by using
only 2 selects.  The internal drives are selected as 0 and 1, and the external 
drives are selected as 0 and 1 on a totally different cable!  Unfortunately,
Tandy didn't put in the pin in the cable on the early 3s and 4s for the
side select signal.  Tandy uses all drives selected as all drives.  The
cable has pins installed for drive 0 only on the slot for drive 0.  This
makes it easy for the usually non-technical customer.  The only difference
that customer must concern himself with is one drive should have a 
terminator pack.  

BTW, if you want to put DS drives on a 3/4, just flip over the cable and then
jumper the drives for 0 and 1 on the drives.  The other side is just grounds
and can stand a few missing pins.

I'll bet the problem with the drive 4 select vs side select is you are using
an aftermarket supplier of drives.  (Maybe the new Tandy drives are standard,
as I think the cable with the disk cartridge now only comes with two slots, 
and the 4 slot cable must be ordered from NP)

				Mike Yetsko 
				trsvax!techsup!bbimg!mikey