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An S100 Bus FPGA Programming and Prototype Board. The first FPGA on the S100 Bus

M

monahan_z

Experienced Member
Joined
Oct 19, 2008
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263
Location
San Ramon, CA
For the past few months I have been working on a very special S100 bus board that contains an Intel/Altera Cyclone IV FPGA board with circuitry that allows it to be used to construct a wide range of S100 boards. One third of the board is available for custom circuity. These would typically just be I/O connectors, a Micro SD card or LCD display etc. The bulk of the functionality will reside in the programmed gates of the FPGA.

A board like this (at least in theory), could be configured to behave on the S100 bus just like any previous “classical” S100 board. All the S100 bus lines interface with individual FPGA IO pins (Input, Output or bi-directional). The next step will be to program the FPGA for UART, SD card drives, Ethernet I/O, CAN Protocols, FireWire, PDP tape and disk drives etc…. Many could exist on this one board alone. A section on the web site will be reserved for users contributions.

I glad to announce that I received the final version of this board from PCBCart and it behaves as best as I can tell exactly as planned.

The board is described here:-
http://s100computers.com/My System Pages/FPGA Board/FPGA Board.htm

I am now opening the board up for a group purchase. Most people here are familiar with the process. (In fact anybody that has not gotten a S100Computers board in the past should contact me directly first) . Please indicate here /URL] if you would like to receive one or more boards. Will take about 3 weeks. Usual PayPal payment when you get your board. The master list will be here. Do not e-mail me directly.

Every few days I will transfer them to here:-
[URL="http://s100computers.com/News%20Page.htm"]http://s100computers.com/News%20Page.htm
from which I will order the boards.

One important point. This is an expensive board to build. The board is a 4 layer board with extra thick copper traces. It will probably run about $32/board (depending on volume). However there are other expenses. The WaveShare Cyclone IV adaptor is $40 (https://www.waveshare.com/coreep4ce10.htm). It requires special sockets from DigiKey ($20), and you will need a “USB Blaster” to program the FPGA (https://www.waveshare.com/product/fpga-tools/altera/usb-blaster-v2.htm) .
That may be the least of your issues. If you have never worked with FPGAs programming them is a whole new world. I use Intel’s Quartus Prime with .bdf files. The above web page introduces you to the approach, but be prepared to sink some time into the effort.

I guess what I’m trying to say is that unlike many of our previous board this is not one where you order a few 74LSxxx chips, slap them on a board with solder and you are up and running. Programming and using FPGAs is a much bigger effort. That said once you get the hang of it the benefits are enormous. After 3 months I’m hooked! The circuit layout capacity of even a Cyclone IV is enormous. One feels like a kid in a candy store!
Please reply on the Google Forum Page ASAP. I anticipate a large “order” volume and will leave the first round open for about one week.

John Monahan
 
Hi Monahan_z,

That FPGA card looks like a wonderful project.

I am still in my infancy with the S-100 bus, at the moment repairing a Sol-20 computer. I looked on your amazing website at the array of S-100 cards.

The one card I would really like to get is The Jade Bus Probe card to assist me with diagnosis & repairs. Do you have one, or a replica of one, that you would be prepared to part with for the right amount ?

Hugo.
 
Chuck(G) said:
Why even bother with the S100 business? Surely, all the functionality could be contained on a index-card sized FPGA board...
Click to expand...

If you have to ask that, you don't know John very well :)


Hugo Holden said:
Hi Monahan_z,

That FPGA card looks like a wonderful project.

The one card I would really like to get is The Jade Bus Probe card to assist me with diagnosis & repairs. Do you have one, or a replica of one, that you would be prepared to part with for the right amount ?
Click to expand...

An interesting piggy-back project would be add USB to the FPGA card - maybe through a cheap FX2LP module. That would allow for distilling the S100 bus signals and sending them real-time over to a modern PC for tracing and analysis. You could even send them raw and just use any sigrok logic analyzer GUI.

Nice work John.
 
Look at John's bus probe:

http://s100computers.com/My%20System%20Pages/Bus%20Display%20Board/Bus%20Display%20Board.htm

John arranges re-orders of boards periodically, look at http://s100computers.com/My%20System%20Index%20Page.htm about half way down the page.

- Gary

Hugo Holden said:
The one card I would really like to get is The Jade Bus Probe card to assist me with diagnosis & repairs. Do you have one, or a replica of one, that you would be prepared to part with for the right amount ?
Hugo.
Click to expand...
 
FPGA are less overkill than you might think. With a set microprocessor or microcontroller - say an 8 core Propeller 2 running at 80 MHz - you have a fixed level of overkill. If you write a program on the prop to bit-bang emulate a peripheral on a 4 MHz S100 bus, I agree, OVERKILL!

If you buy a 5.4 million LUT 3000 ball-grid Virtex Ultrascale chip from Digikey for $76,571, place it on a S100 board, and synthesis 1 AND gate from pins 1 & 2 to 3 and nothing else, do you really have more logic on the board than was typical in 1977? Those sorts of ginormous FPGAs are intended to prototype modern ASICs. A mid-sized FPGA like the Cyclone V on the the board has more than enough logic to prototype a typical ASIC or an entire S100 board from 1977. If that is the scope of the project, it's not overkill. It's the hardware equivalent of using a modern machine to cross compile code you download to an EPROM emulator over USB. It beats the hell out of programming with on-board tools. WRT to FPGAs, designing a complete set of chips and board layout for S100 in a text editor beats the hell out of re-wire-wrapping a gaggle of chips, fixing PtP soldering, or taping-out custom silicon!

If you are unable to buy a 4K RAM chip in 2018 and instead by a 4M RAM chip and zero the upper address lines, did you really buy a 4M RAM chip or a 4K RAM chip for a comparable price? overkill?

It depends on what logic you synthesis in the FPGA that makes it overkill. An FPGA is just a bunch of virtual wires, truth tables, and flip-flops wrapped in ceramic. You can choose not to use 99% of the logic area. With a MCU, the clock is going to tick at (eg) 80 MHz regardless.
 
There's one key difference here that you're not touching on. In 1977, about all you had that was programmable were EPROMs, fuse-link ROMs and second-layer metallization mask ICs and only the first is reprogrammable--all, because of the technology, was pretty stable and not overly complex.

Now, take a modern FPGA. How durable will that be, realistically? Will you get 40 years from the programming? What about replacing the FPGA even 20 years down the road? Given the rate at which devices are evolving, what do you think? Heck, about 10 years ago, I did a design that used the Xilinx XC95128 CPLD. Try to find them now (not the 3.3V version, but the 5V one). The prototype again, was consigned to the junk bucket.

On the other hand, if you're building something that you expect to see destined for the landfill 20 years hence, I suspect that a modern jillion-LUT FPGA would do just fine.
 
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