Thank you for your response Andrew!
The point I was making is this: What is the criteria for choosing a certain bus
as compared to another bus? Is it logistic convenience, or there are other
parameters to take into account?
ziloo :listen:
OK, I think I understand your question better now. I think there are three major factors in the decision to pick a bus for a homebuilt computer bus.
1.) Ease of integration with the CPU. Some busses are going to integrate better with some CPUs just because they are designed that way. See previous response on which busses versus which CPUs. If you are determined and skilled enough you probably can make almost any CPU work with any bus to some degree. The question is how difficult is it going to be and can you leverage any of the existing works already available? If I were going to make a 6800 based homebuilt computer, I would probably pick the SWTPC SS-50 bus since it would integrate well with that CPU. Since I used a Z80, the ECB bus seemed like a logical choice. Picking a compatible CPU/Bus pair also provide lots of working schematics for ideas on circuit building since there are lots of parts documented. For the 6800 example see:
http://www.swtpc.com/mholley/index.html
2.) Availability of parts. Picking a bus has to take into account whether you can get parts for it. The homebuilt computer design is useless unless you can build it. I think this is one of the major problems with kit building for the S-100 bus now is it is so time consuming and difficult to obtain even the most basic parts like bus connectors, passive backplanes, power supplies, prototype boards, and even discrete components like 7805 SCRs. This is where ECB really shines because you can fabricate the passive backplanes out of inexpensive and readily available components from Radio Shack or Jameco (insert favorite vendor here). Making the prototype boards is trivial as well since all it requires is a prototype board preferably 160x100 mm but can be any size and a 96 pin DIN connector 41612. All of which are very common. In addition, the power supplies are cheap and available since a standard PC switching PS will work or any regulated +5 supply will do. You can add other voltages as needed. S-100, ISA-8, ISA-16, and STD-80 all rely on male edge connectors which means you have to buy your own pre-made prototype boards which can really be expensive, assuming you can find them to begin with. S-100 has some unique power supply requirements and each card has its own local regulator which complicates design and construction.
3.) Personal preference. This factor trumps all others. Some people just like certain CPUs and busses and will use them no matter what else. It is a personal decision so who is to say what is right or wrong? If you are determined to put an AMD 29K CPU on a VME bus, no one is going to stop you but you are going to do a lot of work to get there. Have a good time with that project!
Hope this helps. Best of luck with your projects and let me know if I can help in any way. Thanks!
Andrew Lynch
