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Re: Digest Number 2396

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  • ekeefe8051
    Hello, The COSMAC VIP s Super Sound board also shares memory space with the VIP s ROM which is located at 8000h-81FFh. Well it really occupies the entire space
    Message 1 of 12 , Mar 9, 2013
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      Hello,

      The COSMAC VIP's Super Sound board also shares memory space with the VIP's ROM which is located at 8000h-81FFh. Well it really occupies the entire space from 8000h to FFFFh due to lazy decoding (that's a completely different discussion however).

      The registers on the Super Sound board are addressed at:

      8001h - Channel A frequency
      8002h - Channel B frequency
      8003h - Octave selector
      8010h - Channel A Amplitude
      8020h - Channel B Amplitude
      8030h - Enable/Disable Super Sound interrupts

      The ROM only responds to reads and the Super Sound board only responds to writes. They work together fine.

      ED

      --- In cosmacelf@yahoogroups.com, "ajparent1" <kb1gmx@...> wrote:
      >
      >
      >
      > --- In cosmacelf@yahoogroups.com, "joshbensadon" <joshbensadon@> wrote:
      > >
      > > --- In cosmacelf@yahoogroups.com, "ajparent1" <kb1gmx@> wrote:
      > > >
      > > >
      > > > > > *output* ports where ROM resides.
      > >
      > > > People were using that trick back in the late 70s and early 80s to
      > > > get around lack of ram space or recover ram space used up by ROM.
      > > > Even the PDP11 maps out the IO space (its memory mapped) for memory
      > > > when the memory extension is in use.
      > >
      > > It's a very nifty trick, I can't believe I haven't heard of it until now.
      >
      > A flavor of that was widely used where the system booted rom at
      > 0x0000 and the executed a write to the current rom address to
      > switch out the rom. The address ws already decoded and it only needed a flipflop to save the state, reset when reset line is forced enabling rom and preset with rom write happens to disable rom.
      >
      > Many ways to skin that cat.
      >
      >
      > > > > chip families?
      > >
      > > > I know 74H that is a trouble maker as it's a higher threshold and
      > > > may work with cmos, it was trouble when mixed in more conventional
      > > > TTL (74xx, 74LS, 74ALS, 74F, 74S).
      > >
      > > David links to an interesting application note regarding the various families. But your experience with 74H being a trouble maker is well noted.
      > >
      > > Thanks
      > > Josh
      > >
      > > > Generally I don't like to mix families without being sure the
      > >
      > > If you don't mix, you run the risk of inbreeding. Just kidding of course. But I often find 74xx mixed with LS and others on some vintage systems. When I'm building something, I am trying to make do with what I have in my parts stock, so I'll mix and match when I have no other choice. Prototype for production will require a better control, but I'm just fooling around for the most part.
      > >
      >
      > Just know some families mix well like 74xx, 74LS, 74L, 74S, 74AS,
      > 74F and 74AF. You have to respect fan-out and fan-in so the loading
      > is not exceeded (mostly an issue for bussed signals) but they mix well.
      >
      > Mixing 2.7, 3, 3.3V with 5V logic is far more chancy as you must
      > match the level for the inputs or bad things happen. There are
      > parts that mediate that and some of the lower voltage stuff are
      > high input voltage tolerant. Do so with care.
      >
      >
      >
      > Allison
      >
      >
      >
      > >
      > > :) Josh
      > >
      >
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