TI DSDD card prototype "Lewisville" photo

[+FarmerPotato]

David Olson found this example of the TI Double Density controller card prototype.

 

This one uses two TMS2532 eproms and the NEC upd765 double density controller chip.

 

I believe this is the card nicknamed "Lewisville" after the TI office in Lewisville, TX. Back in the day, a Front Range 99'er newsletter editor relied on a Lewisville card and we had an interesting time exchanging files on floppy.

 

I'll have the card at Midwest Gaming Classic. Maybe we will do some elementary troubleshooting on it.

 

Any supporting information is welcome.

 

NEC Datasheet: http://www.cpcwiki.eu/imgs/f/f3/UPD765_Datasheet_OCRed.pdf

 

 

 

 

[mizapf]

Interesting ... similar to the HX5102 Hexbus floppy drive, this controller uses the NEC uPD765 (compatible to the Intel 8272A in the HX5102). TI obviously switched from the Western Digital controllers (WD17**) to this kind, which required a completely new low-level DSR. The upper-level DSR in the HX5102, by the way, is largely copied from the TI Disk controller.

[atrax27407]

Actually, the card uses one TMS2532 (4K) and one Motorola MCM68764C (8K) EPROM. The Motorola chip is the equivalent of the 24-pin version of the TMS2564 which was originally used and is an upwards compatible 8K EPROM. Neither of the TMS2564 (24-pin) or the Motorola chip are available any longer. The only currently available version of the TMS2564 is the 28-pin package and what is needed is a 24-pin package. However, I believe that an AMD AM27C49 would work. We would just have to program one and there is an adapter for the MiniPro TL866 that should work.

Edited March 28, 2018 by atrax27407

[+Ksarul]

As to useful data on this one, I have a pair of these, one that I actually bought as an unassembled kit back in 2000.

 

Here is about as complete a set of documentation on it as is out there right now. All of this is up on WHT or on AtariAge, but putting it here is a good idea too. I recently was made aware of another specification document that I still have to scan in, but the documents here will definitely get you where you need to be.

 

Note: like the HexBus Floppy Controller, the DD format uses 16 sectors per track, so the DD disks can only be read on a Geneve (with any DD controller) or by a Myarc controller if you don't have one of the two TI DD controllers.

A3-TI DSDD-FDC-P1.pdf

A3-TI DSDD-FDC-P2.pdf

TI DSDD FDC Manual and DSDD FDC GPL Interface Manual.pdf

Edited March 28, 2018 by Ksarul

[marc.hull]

As to useful data on this one, I have a pair of these, one that I actually bought as an unassembled kit back in 2000.

 

Here is about as complete a set of documentation on it as is out there right now. All of this is up on WHT or on AtariAge, but putting it here is a good idea too. I recently was made aware of another specification document that I still have to scan in, but the documents here will definitely get you where you need to be.

 

Note: like the HexBus Floppy Controller, the DD format uses 16 sectors per track, so the DD disks can only be read on a Geneve (with any DD controller) or by a Myarc controller if you don't have one of the two TI DD controllers.

 

That looks like really good info. Couple questions. Is your schematic proven and does anyone have one of these that works ?

 

I ask cause I have one that doesn't work and has some trace mods done to it. Don't know where or why.

 

I'd like to get it back to good and that is the first schematic I have seen so maybe there is hope.

[+Ksarul]

The schematic is done from an original schematic RickyDean put up a few months back. It was in rough shape, but between it and the rest of the documentation I have I was able to validate it as far as possible without goinf to my boards and doing a trace-by-trace check. One note I have from BITD on these: all of them were subject to overheating problems for some reason, which is why you often see crazy large heat sinks on them. That's the only way to ensure one of them stays stable for more than an hour or so--and that's pushing it. The boards were only distributed to some of the TI Engineering Group users groups (Dallas got a big batch of them, but there were others) as kits. My first one was one of those Dallas UG kits that had never been assembled.

[marc.hull]

Mine came from Dallas via Grand Junction. Has the way oversized aluminum billet as well. Does yours work ?

[+Ksarul]

The second one I got supposedly works, but I have not tried to use it, based on the warning about overheating that came with it.

[marc.hull]

Well worst thing that could happen is you put some bread on top and make toast 😊.

[+FarmerPotato]

Actually, the card uses one TMS2532 (4K) and one Motorola MCM68764C (8K) EPROM.

I did not see that at first, but it is obvious now. The photos were texted to me and I looked at them on my phone.

 

I have some 2564s for use with the TI EPROM programmer, but I also had an adapter for 2764 that Nick Hulbert put together.

 

-Erik Olson

[mizapf]

Note: like the HexBus Floppy Controller, the DD format uses 16 sectors per track, so the DD disks can only be read on a Geneve (with any DD controller) or by a Myarc controller if you don't have one of the two TI DD controllers.

 

Yes, and (at least the HX5102) distinguishes between 40 tracks and 77 tracks, not 80. This is actually a limitation of the µPD765 / i8272A.

[atrax27407]

The TMS2564s MUST be the 24-pin package. The ones that I have seen are all in a DIP 28-pin package which are unusable for this application. I have been looking for the 24-pin version for some years without success.

[+Ksarul]

I've been thinking about this one for a long while now--it is likely that the 28-pin version of the 2564 will work in the 24-pin socket. Pins 1, 2, 27, and 28 won't insert, but that's OK. 1 is VPP, which we don't need here, 28 is VCC, but so is 26 (24 when used this way), so that problem is covered, and the other two (pins 2 and 27) are chip select pins that don't exist in the 24-pin version of the chip. They expect to be low too, so not connecting them to anything shouldn't cause issues, as the spec allows for insertion into a 24-pin socket.