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Thread: PDP 11/45, Part 6

  1. #21
    Join Date
    Jul 2009
    Location
    Boulder , Colorado USA
    Posts
    2,894

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    Hi All;

    Dave, Thank You for Your Posts..
    "' Before I 'reinvent the wheel', you have tried running the tests contained on pages 2-9 through to 2-17 of http://bitsavers.trailing-edge.com/p...45-MM-007.pdf? ""
    No, and Yes, with Looking at the pages, I can do some things, Like Deposit and Examine, But, I need to go thru these and check them out..

    "" Are you single microcycling or have you slowed the clock down? ""
    I have done Both and each one, one at a time..

    Using the Power Supply, in my Heathkit Microcomputer Learning System, and after I have removed all of the socketed Parts, Which I now can use to test some Parts..
    I have wired up a circuit for the 74S04, and I have put in a Signal and made sure it showed up after wiring it up through all of the Inverters on an Led..
    And they all pass, the ones that I have Socketed on the Board, so six of them are OK..
    Next I will test the 74LS174's and lastly the 74LS74's that I have socketed..
    After that I will wire up a 74S64 to mimick what I see in the Schematic and then I will see what pins I can toggle with my Digital Pulser and with an Led see the Output, I can then go the the PDP 11/45 and make an attempt to toggle that same IC Circuit and see if the Part shows the same behaviour, then change the wiring for the next 74S64, in the 11/45..
    That way I can lessen what 74S64's I will possibly replace.. Since this Board has a boatload of them..

    THANK YOU Marty
    Last edited by Marty; Yesterday at 11:24 AM.

  2. #22
    Join Date
    Dec 2011
    Location
    Oakland, CA
    Posts
    113

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    Quote Originally Posted by daver2 View Post
    The reason for the multiple entries of (for example) FET.00, FET.01, FET.02 etc. (and Fritz can correct me here if I am wrong) is that there are multiple addresses in the microcode PROMs containing the same micro instruction (something to do with how the microcode branching is achieved - i.e. it uses logic to manipulate the bits in the lower part of the microcode). So, the first microinstruction of the FETCH cycle can be found at any of the 10 locations specified in the parenthesis.
    Yup, exactly so! The branching mechanism for the microcode is pretty limited -- for a multi-way branch, the offsets between the various possible target addresses are fixed. So the microcode is fit together like a bit of a jigsaw puzzle in order to set up available target addresses without conflict. Sometimes this means duplicating a microinstruction at multiple addresses, particularly when it must be targeted from lots of different source locations.

    Also, +1 on the sequence of tests that Dave mentioned in the maintenance manual -- they are easy to do and when done in sequence can give a good idea of where to look. I found this sequence very useful when I was bringing up my CPU.

  3. #23
    Join Date
    Jul 2009
    Location
    Boulder , Colorado USA
    Posts
    2,894

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    Hi All;

    Thank You, FritzM for Your Verification..

    On my Testing of the Various Ic's that I have socketed, it looks Like (so far) I have found Four of them that are Possibly No Good.. And one of those didn't Respond at all.. The Others just didn't Look Correct in their Response to my Test, they Responded different than the Good ones..

    THANK YOU Marty

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