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ALTAIR or IMSAI Replacement CPU SBC

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  • joshbensadon
    Hi guys, I m finishing up a project in the N8VEM group that might interest some here. It s a replacement 8080A CPU board for the ALTAIR and/or IMSAI. I am
    Message 1 of 7 , Jun 5, 2014
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      Hi guys,

      I'm finishing up a project in the N8VEM group that might interest some here.
      It's a replacement 8080A CPU board for the ALTAIR and/or IMSAI.  I am building some blank boards, if anyone is interested, the cost of a bare board will be $20ea.

      Features are:

      CPU: 8080A
      UARTS: 2x 8250, RS-232
      RAM: 2x 32K
      ROM: 32K
      I/O: 8 input, 8 output pins
      SPI to SD Card interface & SD Card socket
      ALTAIR & IMSAI Front Panel Connectors.

      The ROM can be permanent or Shadow ROM, selectable in blocks of 8K.
      The RAM can be on or off board, selectable in blocks of 8K
      Where ROM is selected in a block it overlaps the RAM on reads, but writes go through to RAM.
      The CPU can be deselected with jumpers and the board will work as RAM/ROM and I/O for another CPU on the
      S-100 bus.

      Regards,
      Josh Bensadon
    • Bob Applegate
      ... WOM - Write Only Memory. Bob
      Message 2 of 7 , Jun 5, 2014
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        On June 5, 2014 at 11:02 AM joshbensadon <no_reply@yahoogroups.com> wrote:

         


        Where ROM is selected in a block it overlaps the RAM on reads, but writes go through to RAM.

        WOM - Write Only Memory.
         
        Bob
         
      • Bill Sudbrink
        That allows simple code to swap ROM contents to RAM. From: midatlanticretro@yahoogroups.com [mailto:midatlanticretro@yahoogroups.com] Sent: Thursday, June 05,
        Message 3 of 7 , Jun 5, 2014
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          That allows simple code to swap ROM contents to RAM.

           

          From: midatlanticretro@yahoogroups.com [mailto:midatlanticretro@yahoogroups.com]
          Sent: Thursday, June 05, 2014 11:21 AM
          To: midatlanticretro@yahoogroups.com
          Subject: Re: [midatlanticretro] ALTAIR or IMSAI Replacement CPU SBC

           




           

          On June 5, 2014 at 11:02 AM joshbensadon <no_reply@yahoogroups.com> wrote:

           


          Where ROM is selected in a block it overlaps the RAM on reads, but writes go through to RAM.

          WOM - Write Only Memory.

           

          Bob

           





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        • Bob Applegate
          ... Yes, I know. It s been used a lot throughout the years. But it s still WOM, at least until the right soft switch is hit to make the RAM readable ;-)
          Message 4 of 7 , Jun 5, 2014
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            On June 5, 2014 at 11:45 AM "'Bill Sudbrink' wh.sudbrink@... [midatlanticretro]" <midatlanticretro@yahoogroups.com> wrote:

             

             

            That allows simple code to swap ROM contents to RAM.

            Yes, I know.  It's been used a lot throughout the years.

            But it's still WOM, at least until the right soft switch is hit to make the RAM readable ;-)

             

             

          • hornbetw
            You have to read the datasheet to properly use such a sophisticated device! :) Tom
            Message 5 of 7 , Jun 5, 2014
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            You have to read the datasheet to properly use such a sophisticated device! :)

            Tom
          • joshbensadon
            WOM? Sure, I can add some of that. Signetics has data on the 25120 chip, it s 9046 x N, Fully encoded. You can find the data sheet for it online somewhere,
            Message 6 of 7 , Jun 5, 2014
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              WOM?  Sure, I can add some of that.  Signetics has data on the 25120 chip, it's 9046 x N, Fully encoded.  You can find the data sheet for it online somewhere, or I can upload it if you like.

              But otherwise, yes, I would say you are right.  That RAM is WOM until you kill the Shadow ROM.

              PS. I should add, Rich Cini and Don Caprio are planning to release the Mini FP, which would go well with this CPU board.

              Cheers,
              Josh
            • joshbensadon
              Thanks, I knew that data sheet would float up sooner or later. Anyway, I m doing a limited run of these boards, so if anyone wants one, I need to know by
              Message 7 of 7 , Jun 5, 2014
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              Thanks,  I knew that data sheet would float up sooner or later.

              Anyway, I'm doing a limited run of these boards, so if anyone wants one, I need to know by Monday, which is when I'm placing my order.

              Picture of board layout included.

              Regards,
              Josh
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