Backplanes and daughter boards. Connecting the same signal lines to a large number of boards/chips

Why? It's a backplane with a lot of bussed signals. You can use those wires for anything. You can buy a couple of crates on ebay and be experimenting in a week. All the hardware, panels, connectors, and PC board dims are standard.

John

Well yes, the question was whether it was OTT - from a hardware point of view I think it is.

However, if you do use a VME backplane for synchronous serial you have to be careful which signals you use. The data lines, for example, may not have particularly good crosstalk figures between them (they are designed to be driven at the same time, setlle then be strobed). So the AS*, DS0* and DS1* strobes are IMO the most suitable for clocks. The address bus has the same issue. With those caveats, a VME rack could be used, and as you say would speed things up a lot.

Mark.

Having said that, the VMEbus also has SERCLK and SERDAT* signals (up to

32MHz) that could be hijacked for this, in which case you have a ready made synchronous serial backplane.

Mark.

This sounds like a resurrection of the S-100 bus, which sucked because it took all of Intel's crappy control signals and spread them on the bus, but it did account for driving the bus, and terminating and buffering the signals.

Just make sure your drivers have enough OOMPH, and terminate and buffer the signals on the daughters; if you have timing concerns that 1/2 nsec (6 inches) would screw up your synchronicity, then you should probably look into that new PCI stuff or the kind of technology that they used with ECL in the Cray and stuff.

Good Luck! Rich

I don't know about the S-100 bus. I just don't like to put address+data+control onto a backplane. Too many points of failure. Async serial (iow: UART) or manchester is much better since those methods allow for timing errors and are less sensitive to external influences.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
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The '100' in S100 happened because the guy who did it happened to have a bunch of 100 pin connectors around.

John

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Yes, I think I still have a couple of them somewhere in my storage. I can build 25 USB devices on one board. But the USB connectors are nicer to work with then S100/VME bus connectors anyway.

t

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I guess you are too young to remember. Those are the days when we need a whole board for the CPU and another board for the UART. That's why we need a backplane for A,D and C. Nowaday, we hardly need more than half a board.

That, and the fact that the prototype Altair computer was lost in shipment to the magazine. The second prototype was in modular form, built with surplus edge connectors.

If you want fast signals try controller per duaghterboard ala PCIe serial channels.

It sounds like it is just a bit beyond your proven skills, but is it beyond your economical (and timely) learning rate? Yeah, i could come here to resolve that kind of question myself. I suspect that with help it is within your learning rate, usually a better solution for the organization in the long term.

I do not understand how you are applying synchronous to 100BASE-TX. Where in 802.3 does one find it?

Hi! As noted in previous replies, what you are describing sounds a lot like S-100 or PC/XT ISA bus. They are both obsolete parallel busses that are fairly simple to design and use. In particular S-100 is nice to use for an application as you describe because it is simple and the parts are cheap and easy to use. The S-100 form factor is excellent for prototyping because the boards offer 5"x10" area with a lot of PCB space to implement your circuit. There are free EDA templates for both boards for KiCAD available on the internet.

Although most S-100 boards are made using discrete TTL chips there is no limitation to use obsolete or modern CPUs, microcontrollers, CPLDs or even FPGAs. Each board will generally have its own voltage regulators so you can operate with almost any voltage level such as

5V, 3.3V, or less. There is a small but active community of S-100 home brew computing hobbyists still making S-100 boards and the tools needed to make your own boards are either free or very inexpensive. It really is an economical approach to making prototyping and it sounds like it would fit your requirement well.

You can see for yourself at S100computers.com and/or the N8VEM home brew computing project. Good luck with your project!

Thanks and have a nice day!

Andrew Lynch