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Thread: Tektronix 4924 Tape Drive is now working!

  1. #1

    Default Tektronix 4924 Tape Drive is now working!

    I was not able to get the Tektronix 4924 tape drive to accept commands from my Tektronix 4054A computer after I replaced the tape capstan drive motor from an older Tektronix 4923 tape drive that I had.

    I searched for a way to debug the issue - and thought I needed to probe the 6800 bus commands similar to what I had done to find the DRAM issues in my Tektronix 4907 File Manager floppy disk drives.

    After I received an HP 6800 CPU preprocessor module and got the HP 6800 inverse assembler loaded into my logic analyzer, I decided to try the 4924 tape drive again.

    I checked the GPIB address switches and the Mode switches again. I had set the address to 5, but it appeared the Mode was not for the 4051, although I thought I had tried that before. I changed the Mode to 4051, connected the 4924 to the GPIB connector on the top 4907 and tried the command "TLIST @5:" with a good tape installed.

    I got a message that a TAPE was REQUIRED for this command.

    I checked the 4924 Operators Manual again and it indicated the ONLINE switch should be ON for GPIB transfers, so I pressed the online switch and tried the TLIST command again and got the same TAPE REQUIRED message.

    I tried a couple of different GPIB addresses with the command - and got the same message. So maybe something was wrong with this command?

    So I tried a different command "FIND @5:1" - which worked, the 4924 tape rewound to the beginning.

    And the command "OLD @5: loaded the file into memory!

    I don't know why the TLIST @5: doesn't seem to work with the tape drive, but the 4924 tape drive is now working!

    I could use the Tektronix tape copy utility now that I have a second tape drive.

    Since I also just fixed my two 4907 File Managers - I will probably try to archive my precious tape files to the NOS floppy disks I bought for the 4907.

    I think I remember one of the copy utilities copied tapes to disk - I'll do some searching.

    Here is a photo of loading the 4052A/4054A ASSEMBLER program I recovered from the 4924 into the 4054A.
    I picked this angle to reduce the overhead lighting glare on the 4054A CRT.

    The Assembler program uses some of the new features of the "A-series" machines including long variable names - and the CALL "EXEC" which is not compatible with the 4051 CALL "EXEC" to run assembly language programs.


  2. #2
    Join Date
    Sep 2006
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    Great to see it working
    Another bit of hardware I never had the time to do anything with.

  3. #3
    Join Date
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    Nice going (again) Monty.

    I was just re-reading the thread where you introduced yourself to VCFED. What progress you have made with all this Tek equipment in the meantime!

    I might have another go at the 4052/4054 emulator again... See how far I get this time!

    Dave

  4. #4

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    Quote Originally Posted by daver2 View Post
    Nice going (again) Monty.

    I was just re-reading the thread where you introduced yourself to VCFED. What progress you have made with all this Tek equipment in the meantime!

    I might have another go at the 4052/4054 emulator again... See how far I get this time!

    Dave
    Dave,

    I know you can do it!

    And this time I have the 4052A assembler manual listing all the microcoded instructions.

    I should be able to write small test programs to figure out anything we don't find in the documentation.

    Monty

  5. #5
    Join Date
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    Monty,

    I like your optimism !

    I am not particularly bothered about the microcoded instructions to be honest. Since I am emulating the machine at the microcode level, once I get the microcode machine flow sorted out these instruction should just work as Tektronix intended...

    At the moment the microcode self test is bombing out with what it considers to be a hardware error.

    I am spending a little more time this time around in documenting the microcode itself so I try to gain an understanding of what the microcode is trying to achieve.

    I am starting out with the microcode at addresses $300 to $3FF - as these map 1 to 1 with the machines macro instructions. Some macro instructions (e.g. ABA) can execute in one micro instruction. Others can't, so they 'chain' onto further micro instructions in the $0XX, $1XX and $2XX range. I am currently trying to document these additional micro instructions where they are related to a continuation of a macro instruction. What I should have left then are micro instruction subroutines and the start-up and main processing loop of the machine.

    Hopefully then I can develop a flowchart for the microcode and see where that gets me in understanding what is going on with my implementation.

    I have taken a few shortcuts with what I have done internally within my emaulation - but I have commented the bits of logic that I have deliberately left out. My plan was to add this later when I came across some logic that used it.

    Well, that's my overall plan at least...

    Dave

  6. #6

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    Dave,

    My 4052 still needs to be repaired.

    I know the microcode in my 4054A is different than the 4052/4054 microcode - but maybe just new instructions and the old ones should be compatible?

    Monty

  7. #7
    Join Date
    Mar 2006
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    Salt Lake City, UT, USA
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    291

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    Nice job!

    I also have a couple of these kicking around. IIRC, like the external floppy drive, they can also be used with the Tek terminals for offline storage.

  8. #8
    Join Date
    Aug 2009
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    I agree - nice job!
    I absolutely love the progress happening on the Tektronix front here.
    Torfinn

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