Ideas for a simple, but somewhat extendable computer bus

Jon Elson elson at
Fri Nov 17 19:55:37 CST 2017

On 11/17/2017 07:34 PM, Jim Brain via cctalk wrote:
> On 11/17/2017 7:25 PM, Paul Koning wrote:
>> One key question is whether it should be asynchronous, as 
>> the Unibus is, or synchronous.
> I thought synchronous would make for a smaller/simpler 
> design, but could be wrong.
>> A synchronous version of the Unibus would be quite easy; 
>> all the funny one-shot delays would disappear and actions 
>> would simply be taken on the clock edge (rising or 
>> falling, pick one).  Just make the clock period 
>> comfortably longer than the worst case propagation delay 
>> and you're in business.
> Given the CPU landscape, I am thinking < 10MHz, which 
> would seem to satisfy the criteria.
>> I'm assuming it doesn't need to be all that fast.  If you 
>> clock period > prop delay is an issue, things get vastly 
>> more complicated.  If so, you might want to stick with 
>> something that's already been sorted out, like PCIe.
> It does not have to be fast.  I rather thought, "what is 
> the simplest multi-cpu shared bus that could be easily 
> understood by folks and allow them to focus on 
> multi-processing education, not bus understanding"
> Jim
You might also take a look at Multibus and VME, if you just 
want to see how others did it.


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