Need Shugart 851 manual

At 09:04 PM 3/2/02 -0800, Don wrote: 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