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Z80 Homebrew with PSG

Discussion in 'General Electronics Chat' started by RetroFocus2015, Mar 8, 2015.

  1. RetroFocus2015

    RetroFocus2015 New Member

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    1. As I can best describe it, the design is constantly changing in my mind, using parts I now have available. At the moment I have a AT28C256 32K EEPROM on the schematic. With import costs and - I suppose - rarity of older parts it seems a lot easier to obtain the newer parts with the bigger amounts of RAM and ROM on less chips. I think I'll use the 32k EEPROM and cram as much useful stuff on there as possible, like ASCII characters etc.

    2. Something like this http://www.computersmuseum.com/computers.php?KeyNo=39 You could plug just about anything into these expansion ports like joysticks, RAM upgrades, printers, light pens etc using an interface like this one on a TRS-80 http://www.nightfallcrew.com/09/07/...s-80-modello-mc-10-con-espansione-ram-di-16k/
     
  2. RetroFocus2015

    RetroFocus2015 New Member

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    Yes, although I've removed the Memory Bank chip select lines and now have only A15 available, which I was going to use a NOT gate inverter on to switch between RAM and ROM.

    I am still using exactly the I/O configuration from the book. I've just realised that the segment LEDs used for testing use _DSWR5_, _DSWR6_ and _DSWR7_ and the ports use _DSWR0_, _DSRD0_, and _DSRD4_. If I leave the segment LEDS in at this stage, that leaves me with _DSRD_ 1,2, and 3 and likewise for _DSWR_.
     
  3. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Its conventional to use MREQ for ROM/RAM and IORQ for any peripherals.

    Is it possible that you could post a copy of the circuit that you are using as a starter.?
     

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