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Thread: Overview device addresses PDP8 Omnibus systems

  1. #1

    Question Overview device addresses PDP8 Omnibus systems

    Hello everyone,

    Is there an overview of the device addresses for Omnibus devices?
    I've seen that some different devices can be set at the same device addresses.

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  2. #2

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    Quote Originally Posted by Roland Huisman View Post
    Is there an overview of the device addresses for Omnibus devices?
    I've seen that some different devices can be set at the same device addresses.
    At the back of every edition of the Small Computer Handbook are tables of IOTs for the peripherals. In the 1973 edition (e/m/f), table 9-5 on page 9-33 also gives an overall summary.

    Hope that helps!

    Vince

  3. #3

  4. #4

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    Hi Vince,

    Quote Originally Posted by vrs42 View Post
    At the back of every edition of the Small Computer Handbook are tables of IOTs for the peripherals. In the 1973 edition (e/m/f), table 9-5 on page 9-33 also gives an overall summary.
    That was fast! Thanks!

    For the serial cards this seems the standard according the info of Doug Jones.

    03/04 console default
    40/41 usual second TTY
    65/66 usual serial printer

    I want to add another serial card and the one which I have here was already set to 34/35.
    According the list this seems to be unused address space. So not a problem to use it here.

    Storage systems seem to have overlapping addresses? I've spotted that already with the RX8E and TA8E.
    The range of 70-77 is used for the TM8E, TD8E, RK8 and TC08 according that list.
    And the TA8E and RX8E seem to be in the same address space. I was planning to put some
    more devices into my 8/E but I might run into some addressing space problems...

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  5. #5

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    Quote Originally Posted by Roland Huisman View Post
    Storage systems seem to have overlapping addresses? I've spotted that already with the RX8E and TA8E.
    The range of 70-77 is used for the TM8E, TD8E, RK8 and TC08 according that list.
    And the TA8E and RX8E seem to be in the same address space. I was planning to put some
    more devices into my 8/E but I might run into some addressing space problems...
    I imagine that certain combinations were not expected to be used. For example, why have a TC08 and a TD8E? So they may have decided to re-use same address for controllers that share a device type. Not sure what the thinking was for the other tape devices.

    Then again, at some point I suspect that there were more devices than addresses, so then it becomes just a question of which combinations seem unlikely.

    Vince

  6. #6

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    Quote Originally Posted by vrs42 View Post
    I imagine that certain combinations were not expected to be used. For example, why have a TC08 and a TD8E? So they may have decided to re-use same address for controllers that share a device type. Not sure what the thinking was for the other tape devices.

    Then again, at some point I suspect that there were more devices than addresses, so then it becomes just a question of which combinations seem unlikely.

    Vince
    There is definitely way more devices than addresses. Not helped by the fact that the number of functions available on one device is small. So some more advanced controllers grab a whole range of addresses. Even the simple serial controller grabs two device numbers. And then the memory extension grabs 8 device numbers, the CPU grabs one...

    So no way of putting every controller that exists into one and the same system. However, no software that I know of would be able to handle that either, so I think it's a rather theoretical exercise.

    DEC certainly did try to group similar type of devices onto the same addresses, since it seemed likely that you would only have one of them.

    But for most controllers, you are actually free to select any address you want, so just assign things as you go along, and you'll be good. A few controllers were a bit limited, so cater for those first, if needed. And of course, a few makes sense to really allocate to "standard" numbers, like the console terminal.

  7. #7

    Default

    Quote Originally Posted by fpw View Post
    Thanks a lot for that nice overview. I totally overlooked your reply somehow...

    Quote Originally Posted by bqt View Post
    There is definitely way more devices than addresses. Not helped by the fact that the number of functions available on one device is small. So some more advanced controllers grab a whole range of addresses. Even the simple serial controller grabs two device numbers. And then the memory extension grabs 8 device numbers, the CPU grabs one...

    So no way of putting every controller that exists into one and the same system. However, no software that I know of would be able to handle that either, so I think it's a rather theoretical exercise.

    DEC certainly did try to group similar type of devices onto the same addresses, since it seemed likely that you would only have one of them.

    But for most controllers, you are actually free to select any address you want, so just assign things as you go along, and you'll be good. A few controllers were a bit limited, so cater for those first, if needed. And of course, a few makes sense to really allocate to "standard" numbers, like the console terminal.
    Well the first moment I noticed it was when I was drawing the TA8E clone (TU60 controller). This card can be set in
    exactly the same address range as the RX8E clone (RX01 controller) which I have drawn before that.
    That is probably why OS8 want the RX8E set an 75 and the default address for the TA8E is 70.

    But it is good to be aware of the possible conflicts here.

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

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