Next Lomas project - Thunder 186

[RichCini]

To conclude this thread, the Thunder 186 reproduction works. The first board run was borked due to a bad CPU footprint (although a PLCC68 footprint, the pinning is non-standard). Second run works fine with two minor provisos. I've had it running with 640K of RAM (256k on-board plus 384k of off-board RAM using CompuPro boards) and plain old PC/DOS 3.3. Project files are here (https://github.com/RichCini/LomasBoards/tree/main).

I would really like to get a mass-storage board working, like the Lomas SCSI board. But, I have not been able to surface a copy of the manual or schematics anywhere. With that, I could possibly get Windows 1 running...maybe.

 

[Hugo Holden]

For this application, RAM parity checking can be removed. The 74LS280 parity checker (U51) can then be eliminated, and the "parity error" signal it generates can be forced to an "always OK" state.

A little OT, but I really like the '280 parity checker IC. I found a really oddball use for one in a Static Tic Tac Toe computer I designed. I used its odd & even outputs in conjunction with some gates wired as a data selector as a "game sequencer" to figure out when the computer should make a move, depending on who started the game first, the computer or the human. The circuit is on page 11:

www.worldphaco.com/uploads/THE%20STATIC%20TIC%20TAC%20TOE%20COMPUTER.pdf

Without that 280 chip the whole problem would have been a lot more awkward to resolve.

 

[channelmaniac]

I understand that AST Research used the VL4501 in their PCjr sidecar memory, but I can’t find a manual or schematic of it.

Here ya go.

 

[norwestrzh]

A little OT, but I really like the '280 parity checker IC.

Just saw 74AS280 for sale on www.theelectronicgoldmine.com for $1.10.

[I have absolutely no affiliation with the above mentioned site.]

Roger