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Thread: Honeywell 200 resurrection

  1. #161

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    Excellent progress. Still trying to view the attachment, but something is wrong. Sent a note to the administrators. Is that same diagram available on your HoneyPi web site?
    - Doug

  2. #162
    Join Date
    Sep 2012
    Location
    Kent, England
    Posts
    140

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    Honeypi Control Memory Map.png

    I don't know what went wrong there. Is this okay?

    I took a look at the emulator on your website, which is equally impressive. If only my project could be completed so quickly. Thanks for that video of my programme running. My rudimentary test emulator doesn't have graphics. I threw it together just to ensure that the Pi programme worked.
    Last edited by RobS; December 1st, 2019 at 12:15 AM.
    Rob - http://www.honeypi.org.uk
    The Internet is a winch to get your project off the ground ... but always have a parachute handy.

  3. #163
    Join Date
    Sep 2012
    Location
    Kent, England
    Posts
    140

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    I mentioned previously that I had to assemble some replica boards for the main memory, so here is a picture of one of them next to an original to illustrate the lengths to which I am prepared to go to maintain authenticity. It is worth doing this in the main memory section whereas the control memory is my own design, so only functionally similar to the original.

    2MSS4 replica board.JPG

    Board B on the left is an original manufactured in March 1969 according to the date stamp on it while board H on the right is a replica. The PCB was made by my friendly professional PCB manufacturer from my design files and so far as possible I used original components removed from spare boards. Certainly the transistors are all originals as they have proprietary Honeywell part numbers and I don't know their characteristics and the majority of the other components also are. The most obvious variation from the original is that I omitted unused edge connector pins to keep down the cost of gold plating them, which is a significant part of the manufacturing cost. Modern PCB design software lays out straight tracks, so I had to use a copper layer overlay in the design artwork to create an accurate copy of the original while still providing the manufacturer with industry standard files to feed into their automated machines.
    Rob - http://www.honeypi.org.uk
    The Internet is a winch to get your project off the ground ... but always have a parachute handy.

  4. #164
    Join Date
    Sep 2012
    Location
    Kent, England
    Posts
    140

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    Oh dear, I just noticed an error on my control memory diagram. It shows sixteen bits in the main memory address register whereas there are only fifteen just as in the other registers. The type 201 processor only catered for two and three character addresses, i.e. twelve and fifteen bits, supporting a maximum memory size of 32k characters.

    The control memory always uses fifteen bit addresses within its registers and the only requirement to make twelve bit addressing work correctly is that the increment/decrement function turns off carries to the top three bits and the character loading function doesn't change them either. As a result operations while in address mode two are confined to a single 4k bank of memory with memory wrap-around occurring within it. Of course different registers could be pointing to different 4k banks, but personally I've never tried exploiting that "feature" in a programme. As whole registers get copied one to another during normal operations any differences in the bank bits would quickly get erased, so it was never intended that the registers be used like that, I suspect. I have written mixed mode programmes which switch from one mode to another in different sections of the code, but it had to be done carefully. Designing a replica machine or even a software emulator which exactly emulates the original machine isn't actually that easy because of such quirks, but that is all part of the fun (if that's the right word to use) in this type of work.
    Rob - http://www.honeypi.org.uk
    The Internet is a winch to get your project off the ground ... but always have a parachute handy.

  5. #165

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    Thanks, Rob. I can view these latest attachments. It is great to see those old (new) boards up close! And the block diagrams, and details like this latest post on address handling, will help keep me honest with my "virtual hardware".
    - Doug

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