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Thread: Printer port model 4

  1. #1
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    Default Printer port model 4

    I was looking at model 4 printer port schematic while thinking about a printer to connect.

    In my mind I had always thought only 4 or 5 bits were available on read of port. While looking at schematic I realized it appears it passes a full 8 bits bidirection.

    Is this correct? I have not yet actually done any tests, schematic research only.

    Thanks

  2. #2

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    Yes, it's the basically the same Centronics parallel port scheme as used on PCs, and only four of the input signals are standardized (connector pins 21, 23, 25, and 28), but, as the Model III technical reference manual says, "A full eight bits of data are buffered so that the Line Printer Interface could be used for any general purpose parallel interface". The other four inputs are pins 19, 29, 30, and 32. You should be able to count on this in any Model III/4/4P/4D. The Model I, on the other hand, only had the four standard inputs.
    -Alan

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    Quote Originally Posted by Petrofsky View Post
    The other four inputs are pins 19, 29, 30, and 32. You should be able to count on this in any Model III/4/4P/4D. The Model I, on the other hand, only had the four standard inputs.
    Yes, but what I am saying is looking at schematic it appears it has 8 bits buffered on input not a nibble.

    I have never tested if I can read all 8 bits as I thoght only a nibble of data on read was available.

  4. #4
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    Ok after I reread your last sentence it looks like your saying model 1 has a nibble and model 3/4 a byte?

  5. #5

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    That's right.
    -Alan

  6. #6
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    Quote Originally Posted by Petrofsky View Post
    That's right.
    Too bad that input dont come with interrupt signal or a strobe bit that showed data available for input.

    As far as IBM, dont it really have just 4 on input or maybe it was very early days of clones that some versions only had a nibble input.

    Which reminds me. I did not have a RS franchise but did service TRS80s and write programs. We did have JimPak which was a product by Jameco.

    This lead to us having almost 5 of every item in Jameco catalog. When we closed in 1999 I kept a great deal of components etc.

    I just found an unsold book I plan to put on ebay soon that is a complete book of " IBM PC parallel port ". It is a highly technical book pretty thick.

    As memory serves me we sold these at time laplink was new and all the craze. People were studying IBM design of printer port.

    Different subject, but I just found a box new SIP to SIM converters I saved. Man that brings back memories.

  7. #7
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    Been researching PC parallel printer port and by George I think I was right, PC only has a nibble available on read of port.

    TRS80 has a byte proving once again TRS80 superior design.

  8. #8
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    There's also a couple of lines that have the signals changed around. If you connect a PC to a TRS-80 printer or vice versa without changing the correct lines around, you can damage the computer or printer. TRS-80s have a Centronics compatible printer port, where IBM modified the Centronics port on the PC.

    Tom

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    Quote Originally Posted by hornbetw View Post
    There's also a couple of lines that have the signals changed around. If you connect a PC to a TRS-80 printer or vice versa without changing the correct lines around, you can damage the computer or printer. TRS-80s have a Centronics compatible printer port, where IBM modified the Centronics port on the PC.

    Tom
    IBM always has to be special and odd.

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