Need Shugart 851 manual

From: Joe <rigdonj_at_cfl.rr.com>
Date: Mon Mar 4 08:01:01 2002

At 09:04 PM 3/2/02 -0800, Don wrote:
>
>
>On Sat, 2 Mar 2002, Joe wrote:
>
>> Thanks for posting these. I know that I just asked for the jumper
>> settings but I think I'm going to need more. I want to replace some Shugart
>> 800s in my Intel MDS with the Shugarts 851s and I've been studying the
>> interface, wiring and S 800 setup and Intel has cobbled up a truely
>> bizzarre setup and I think I'm going to need the whole OEM setup manual for
>> the 851 so that I can find out where to make some of the circuit
>> modifications. A couple of people have already promised to get me a copy.
>> Thanks.
>
>Joe, in a `normal' Shugart drive installation, a switch from SA-800/1 to
>the SA-850/1 is almost a dropin replacement. If it is more than that,
>Intel must have engaged in some `hanky-panky' with their circuitry.


    Oh, they've engaged in lots of 'hanky-panky'! Let me tell you about
just one thing that I've found so far. I started checking the cables from
the dirve controller all the way out to the drives in their external drive
box and I found that each drive had a small circuit card that plugged in
between the drive connector and the ribbon cable. On the circuit card is
two jumpers marked S and R. Each has two positions; 0 and 1. I checked to
see what they did and found that S connects to DS (Drive Select) line 1 or
DS line 2 coming from the controller card BUT the common pin on the S
jumper connects to BOTH DS 1 and DS 2 inputs to the drive. This is hard
wired so it can't be changed. Now I wondered what they hell they were
doing selecting TWO DS lines simultaniously so I started checking the drive
itself. It turns out that there is a way to address up to 8 drives per
system instead of the usual four and that Intel is basing their addressing
on that method. What they've done is to remove all the DS jumpers on the
drive and add a 74L85 (IIRC) four bit comparator IC. The four DS inputs fed
the B inputs of the comparator and they use three pairs of pads (D1, D2,
D4) on the drive to fed three of the A inputs. But wait, they're using
four inputs on one side but only three on the other. Somethings wrong.
Well the A0 input is permanently active (Low = active) and only the three
upper lines are used for setting the address. Since A0 is permanently low
that means that B0 also has to be low (active) to select the drive. That's
why they tied DS1 to DS 2 (DS 1 goes to A0). They've also added a line from
the A=B output of the comparator back to the output of the original drive
select circuitry (via pad DDS) to enable the drive when the correct address
is recieved. The crazy thing about this whole affair is that the drive
controller can only select one DS line at a time. It is not capable of
being used in a binary mode! So all of this added complication is utterly
useless! If you look at the jumper listings that you send me for the 851
drives you'll find that there are no Dx or DDS pads listed so there's one
big difference there and I haven't even started to look the "complicated"
stuff yet! That's why I need the complete manual.

   I could probably remove the comparator and use the DS jumpers but there
may be other things involved too and I'm trying to keep everything as
original as possible.

   Also I found that they're using one of the "alternate I/O pins" (# 16)
for something but I haven't traced it out yet.

   FWIW I found that the "R" jumper on the added circuit card is used to
route the "Ready" signal from the drive back to the correct Ready line on
the cable that goes back to the controller card.


   Just for a little backgraound. This is an Intel Series III model 235 MDS
with the model 202 Double Density floppy drive controller added. The
external drive is an Intel model 720. It holds two Shugart FH model 800 8"
floppy drives. The control card can handle up to four external drives (two
chassis) and has four Drive Select lines and four Ready lines but the
output cable splits into two and connects to two rear panel connectors, J8
and J9, so each connector (and therefore each drive) only has two select
and two ready lines. Each connector can be used to connect to one external
drive chassis (two drives).


    Joe

>
>Good luck!
> - don
>
>
>
Received on Mon Mar 04 2002 - 08:01:01 GMT