:The idea isn't bad though, that way it becomes independed of whether or not software runs at 300Hz. Well, most or all software DOES run at 300Hz so that solution doesn't improve too much. It might fix problems where AMX Art disables IRQs and misses some interrupts.
:Only problem would be if Com isn't pulsed. A (rather rare) situtation where this could happen: If software is plain mouse controlled, and doesn't use sound/keyboard - then PPI/PSG would need to be initialized only once after power-up, and so Com won't pulse after that initialization.
:> The diode in the 74LS145 isn't specifically there to pull the signal up, it just happens to have that effect.
:Strange. Then it isn't OC at all. Do you really get Com=5V; when the mouse interface isn't connected? My CPC outputs only short 1V level, no long 5V levels. And can you upload the datasheet page somewhere? I'd bet two EPROMs that you've misread it... maybe the diode pulls down spikes above +5V or so?
:> I dropped the voltage on the CPC to 4.5V to simulate heavy hardware load...
:Wow, I never got so far when testing. Maybe that's why I am sometimes running into problems, with circuits that work on one computer, and not on another :-)
:Your tests didn't really cover timing stuff (ie. the situation where you need Com to get HIGH quickly), only voltage loads. --[[User:Nocash|Nocash]] 13:43, 10 April 2010 (UTC)