P1 used in new Apple1 retro board

P1 is used as the Apple Video Chip Clone.
But I wonder why Apple1 video ic was designed so poorly like as terminal, like a printer before monitors was available.
But unlike a printer the whole screen needs to be buffered anyway, so why not use its RAM in a more Random Access way?


  • 3 Comments sorted by Date Added Votes
  • potatoheadpotatohead Posts: 9,091
    edited November 2017 Vote Up0Vote Down
    That is due to how the Apple 1 was created. Woz got inspiration from Don Lancasters TV Typewriter project back in the day. And it was very common to just stream data over (slow) serial.

    The TV typewriter was done using discrete logic. What Woz did was just tack a computer (6502) and a little ROM on to it.

    Memory mapped display came in the Apple 2.

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  • Oddly enough yes.
    According to the documentation on the Apple 2 and the Apple 2 Plus, and even the Apple 2E, (side note I got my start on both the Plus and the 2E designs.) all did indeed use memory mapped I/O and also video memory.

    The R6502 used memory mapped I/O as its communications style. Which is of course anathema to people who got started with various examples based on the PC, or even examples descended from the I8080. Which includes the Z80. Video displays for the Apple all used memory mapping, and naturally the PC and its friends used other methods.

    Oddly enough our own Phil Pilgrim and his Prop Backpack useful for putting graphics and text onto a video screen behaves in a fashion similar to the engine behind the typer front end for Don's TVT cookbook contents.

    And I decided to make use of the Basic Stamp members for running my gadgets. Originally I had an idea to adapt that system (The TVT Cookbook contents) for putting text onto a screen. Let's just say it didn't workout, but obtaining a Prop Backpack did, and the problem got solved. Now? I'm still looking into convincing a Prop to do much of the same.
  • Cluso99Cluso99 Posts: 13,369
    edited November 2017 Vote Up0Vote Down
    I have fond memories of the Apple //e, ///, etc.

    The Apple //e could only pass data across the bus the cards at 1200bps before it would drop characters. I designed a board which could use ~56000bps without losing characters which I held a patent for. Our card connected to IBM mainframes using synchronous comms and contained its own Z8 processor. The Apple //e could do file transfers and/or act as a 3270 video terminal to the IBM mainframe. Fun times around 1983 :)

    One of the nice video cards for the Apple // was the Zofarry Video Card, again designed in Oz, by Harry Zofarry (yes his real name).
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