Subject: [stella] PIA/(RIOT) "undocumented' feature From: Mark De Smet <de-smet@xxxxxxxxxxxxxxx> Date: Fri, 5 May 2000 22:59:48 -0500 (CDT) |
In doing some reasearch into the VCS memory map, I've discovered something interesting about the PIA. I was going through the datasheet for the chip(you can find it at www.6502.org), and noticed that it has interupt generation capabilities. Schematics show that the interupt output pin is left disconnected, but there is an interupt flag register. It can generate interrupts for timer overflow and from edges on PA7 (which is joystick 0 right or paddle 0 button). Reading a flag to tell if the timer overflowed is kinda useless because simply loading the value of the timer, and checking the zero bit is much easier.(technically they are different in that the overflow interupt bit is set once the overflow has occured(ie wrapped to FF), but I can't imagine how this would be helpful) However, you can use this as an edge (positive or negative) detection circuit on this joystick/paddle line. This could be used with some external hardware, or if you are using P0 paddle button, and are concerned about catching the fastest presses.(or want to know about the button release, but don't care about the press) This can be used in the same way as the latches on the joystick trigger buttons.(but in this case for paddle 0) I mention this, not because I have a use, but because I'm sure that the creative people on this list can come up with some good use for this. Ideas? Mark -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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Re: [stella] 650X Assembler, John K. Harvey | Thread | Re: [stella] PIA/(RIOT) "undocument, Peter Storey |
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