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Thread: How to burn 2708s

  1. #1
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    Default How to burn 2708s

    I'm hoping someone might be able to give me a plain English primer on how to burn 2708 eproms. My second SWTPC 6800 came with a Micro Works 2708 burner. I was thinking I might employ it to burn a different monitor for my MSI 6800.

    What I'm trying to understand is sort of how I would get a dump of the desired monitor onto the 6800 and then how to burn it. I have the Microworks instructions.. I think what I'm after is just the general concept. I'm wondering things like.. do I have to set it to go to specific addresses? What happens of the amount of data exceeds the capacity of the chip?

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    Don't know about your particular burner, but I do remember 2708s.

    3-rail power supply, no elegant algorithms--essentially you keep banging on a cell until it takes, then bang a bit more for good measure. Programming is very slow in comparison to modern UVEPROMs.

    I'd prefer to use single rail 2716s (not the TMS2716s, which are still 3-rail)--and burn the same data twice. 1702A, 2704 and 2708 were early devices with all of the problems attached thereto.

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    Lets look at the questions in details...
    ... assuming the manual for you burner is this one:-

    http://www.swtpc.com/mholley/MicroWo...oWorks_B08.pdf

    and you are using paper tape, cassette tape, or emulated cassette tape..

    1. You need to create an object code copy of the desired ROM monitor.

    If you have the source assemble to produce a MIKBUG format object tape.
    If you have a MIKBUG tape then you are set to go.

    2. Use the programmer software to program load the data into RAM

    The programmer utility software will allow you to load the tape into memory using the "LOAD" command.
    Assuming the code is designed to run at C000 you need to tell the utility to subtract C000 from the start address on the tape so it loads the data into the RAM at address 0000

    3. Check the blank ROM is blank

    The Programmer software will let you check the ROM is blank. Use the "E" command.

    4. Use the Burn command to PROGRAM the ROM

    5. Use the V command to check.

    6. If you have more than 1K to program then put a new blank e-prom in the programmer

    7. Use the M command to move the data for the second eprom down to low memory

    goto step 3...
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals

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    Thanks muchly Dave.

    I guess the first hangup is the means of getting the code to the computer. Right now the only means of getting data into and out of this 6800 is via tape. I'm just not sure how I'd get what I need onto tape from whatever modern PC I downloaded it from.

    I'm wondering if this will work. Basically I'm trying to replace the ROM on this MSI 6800 I have. It is supposed to use MSIBUG but it was changed to something called WEEBUG which is dramatically stripped down and lacks functions like memory examine, load, etc. Since I'll likely never find a copy of MSIBUG, I thought I might try switching it over to SWTBUG or MIKBUG. But I don't know if the MSI will run it as I assume the different 'BUGs' look for specific hardware in specific locations... like the serial cards, etc. I actually tried swapping the 6800 board from my SWTPC into the MSI once (with ram).. but it wouldnt work.
    Last edited by falter; April 25th, 2017 at 10:57 PM.

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    You should be able to rig a PC up to emulate the tape. Its "just" RS-232...
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals

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    So I'm finally getting around to trying this. I have my DREAM 6800 'CHIPOS' which is to be burned to a 2708. But reading and re-reading, I'm still not clear on how one gets the code printed here:

    https://drive.google.com/file/d/1rek...ew?usp=sharing

    Into this 'object code format'.

    Can anyone explain to me, like i'm a 5th grade who knows *nothing* about this stuff, how you'd go about doing that, for the purposes of trying to burn it with my SWTPC's 2708 burner? Dave mentioned something about making an 'object code copy' but I have no idea whatsoever how to do that.

    If I understand the way this particular card works, I could just manually enter the bytes, but starting at 0000 rather than C000?
    Last edited by falter; January 1st, 2018 at 12:40 PM.

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    That's certainly a way to do it. In the early days, before magazine publication methods like Paperbytes or the Cauzin Softstrip, that was the only way to do it.

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    I don't think anyone has produced a text file of this particular code.. so yeah.. I guess I will have to enter it. I'm curious though.. if I enter it from 0000 rather than C000.. how does it end up at the address the computer will be looking for it at? Or is it just that it writes from the beginning of the EPROM and the computer itself is wired to treat that EPROM as being at C000?

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    Yes, you start with 0000, since that address is the displacement within the EPROM.

    Your address decoding circuitry places the contents of the EPROM at a given CPU address. Note that a 2708 has only 10 bit of address lines. Address decoding circuitry supplies the other 6.

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    Thanks Chuck. So.. say I didn't have my SWTPC but a PC programmer instead.. and all I have is the code on that scanned page.. I'm assuming I'd have to write those hex values into a text file (hex or something?) and then somehow convert to binary?

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