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I was planning to setup the keyboard hardware for reading the joystick and then doing lots of IN instructions to read the state and fill memory.
Then save the data to disc and look at it on the pc and work out what the interface is doing... I don't know if my code will effectively keep Com low or not.
But maybe I will answer some things???? Who knows.- Arnoldemu :> when the Art package is running and you'll see it's not permanently low:Okay, checked. True, it's pulsed at 300Hz. The reason is that the software does completely reconfigure the PPI and PSG (normally it would need to do that only after keyboard scanning). Other software may or may not do it the same way. Anyways - that's irrelevant, the circuit should work fine no matter if Com is pulsed or not.:> Besides that, the software also reads the keyboard:Yup, as I said.:>the AY-8912 which is a latch:It is a latch? For sure: it isn't! Or do you mean the output direction? Anyways, doesn't matter, too.:>reference the 74LS145 Datsheet ... diode with ... 17K:An open-collector output with 17K pull-up diode? What is that? I checked a bunch of datasheets, but couldn't find any mentioning such a bizarre thing. What datasheet was saying that???:If you measure the Com pin, you'll see it's always LOW, with some short +1V edges. If you attach a pull-up, the signal looks inverse: Always HIGH, with some short 0V edges. As I said, the 74LS240 in your circuit might maybe work as pull-up, the 74LS145 in the CPC doesn't do so.:>pull-up resistor to "sharpen the edges" of the signal isn't required.:Makes sense for low frequencies. Though the inputs are read at falling edge, aren't they? Well, okay, you are right, the falling edge should be stable, only the raising one would be improved by pull-ups.:> the circuit works perfectly well without it.:Great.:Just to be a pain... Did you think about worst case scenarios? Like one programmer reading the keyboard immediately after the mouse/joystick input... Maybe then the raising edge could be important :-) --[[User:Nocash|Nocash]] 16:53, 9 April 2010 (UTC)
