stephen_usher wrote: ↑
Fri Nov 20, 2020 7:39 pm
I'm mostly using @derkom's design. It's switching the bus arbitration and some outputs. I've added controlling the /HALT line. The CPU which isn't in use has the /HALT line pulled low so that it's constantly halted and has all the address and data lines in tristate so that they don't load the buses.
Ah ok, I’m not familiar with Derkom’s design, but it sounds like that’s doing the right thing if you’ve added HALT to it.
HALT by itself, at least on the 60830 which I know you half on half of your board, doesn’t tristate the lines, it just ‘stops activity’. The data lines, for example, are still asserted. This caused me problems on my Falcon card when I failed to understand this. Both CPUs fight.
Holding BGK is the simplest way to tristate the pins, but negotiating is obviously superior.
Just thought I’d mention it in case one or both your chips are running hot.