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14208Re: [cosmacelf] RCA VIP keypad

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  • Ray Sills
    Jul 1, 2013
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      Hi Scott:

      IIRC (since I don't have my VIP manual here at my desk) there was a
      dump of the monitor code in the the RCA VIP book. In any event, there
      is a disassembly of the ROM in the RCACOSMAC Yahoo group. Go to the
      files section and look for VIPER Volume 1, issue 3.

      I think EF3 generates an interrupt and that routine scans the keypad
      leaving the hex data on the data bus. The running program can then
      pick up the nibble and process accordingly.

      73 de Ray

      On Jul 1, 2013, at 6:18 PM, somaspack wrote:

      > Hi,
      > The manual for the VIP doesn't go into the details of the ROM
      > monitor. I am curious how the keypad functions. It uses a 4515 4-
      > line to 16-line decoder, the inputs are D0-D3, the outputs are
      > connected to the individual hexadecimal switches, the common end of
      > all switches are wired to EF3.
      > So I suspect that when run, the VIP polls each switch in a loop
      > (0-15), and addresses the 4515, places the relevant nibble on the
      > data bus to enable the key output, and if the key is found pressed -
      > EF3 goes high which would then trigger a branch operation to handle
      > the key press.
      > Does this sound correct? Thanks.
      > Scott
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