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    >>> The only OUT's in the ROM are to set up the...

    >>> The only OUT's in the ROM are to set up the Z80 PIO, so the page switching must be controlled directly by hardware.

    Good thinking.

    >>> I’m in Germany.

    I used to work in Erlangen and...
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    Welcome to VCFED. You will need a multimeter...

    Welcome to VCFED.

    You will need a multimeter and a logic probe as a minimum to perform fault finding.

    To repair any faults you find will generally require soldering and desoldering skills.
    ...
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    Just thinking aloud here... Is the PAGE...

    Just thinking aloud here...

    Is the PAGE feature a function of the MONITOR ROM (i.e. firmware) or hardware?

    Just thinking that when you run the hello world program the screen will have the READY...
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    +1. Yep, that’s the mystery solved. Two pages...

    +1.

    Yep, that’s the mystery solved. Two pages of 512 bytes.

    One page from 0xC00 to 0xDFF and the other page from 0xE00 to 0xFFF.

    So we should now be able to write “hello world!” on one page...
  5. You could always invert the clock signal... ...

    You could always invert the clock signal...

    Checkout the PDP-8 LD12 - this is an existing design for exactly what you are trying to do!

    Dave
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    I suspect there would have been an additional RAM...

    I suspect there would have been an additional RAM card that you don’t have...

    Fig 13 of Don Lancaster’s TVT article (https://www.tinaja.com/glib/Kilobaud_TVT_Hardware_pt2.pdf) describes the CG5004...
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    I dug my little Z80 wire-wrapped board out... ...

    I dug my little Z80 wire-wrapped board out...

    Z80 CPU, 8K RAM, 32K EPROM, Z80 PIO (no SIO though), SP0256 speech synthesizer, LM386 amplifier, MM74C917N driving 4 off 7-segment LED displays,...
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    The initialisation code at address 0x0088 invokes...

    The initialisation code at address 0x0088 invokes RST 0x08 which initialises registers DE, B and A and then falls through to the code that is within RST 0x10 to actually clear 256+256=512 bytes...
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    I assume when you press the 'g' key, the monitor...

    I assume when you press the 'g' key, the monitor responds with the text message "GH TO". I assume this should be "GO TO". We can now fix the bug :-)!

    I suspect the screen size is really 1024...
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    You beat me to the post about most of what I have...

    You beat me to the post about most of what I have scribbled down on my bit of paper.

    I agree that the command set appears to be 'g' and 'l' (lower case).

    The screen (I suspect) is 1K starting...
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    I have disassembled the EPROM contents (see...

    I have disassembled the EPROM contents (see attached). Obviously, the dissassembler does not understand text messages!

    It looks like it uses interrupts (IM2).

    The stack (and hence RAM) should...
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    If it is a 'commercial' piece of equipment you...

    If it is a 'commercial' piece of equipment you have, then the reset circuitry will be a bit more complex than a CR network.

    As a minimum, it should have some schmitt trigger inverter logic to make...
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    I can get DECUS 8-102A working exactly as Vince's...

    I can get DECUS 8-102A working exactly as Vince's instructions.

    The TAP file appears to have a simple loader on the front of the tape which is confusing SIMH. Well, SIMH is doing what it is told...
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    +1 for Vince's post #2. I'll give it a go...

    +1 for Vince's post #2.

    I'll give it a go myself tomorrow and try it out...

    Dave
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    Pip, If you are happy - it ain't broke - so...

    Pip,

    If you are happy - it ain't broke - so don't fix it...

    If something happens to the focus in the future - you know where to come for advice!

    Dave
  16. How have you got the links set on the serial...

    How have you got the links set on the serial board for P60 to P63?

    Have you got RTS looped back to CTS and DTR looped back to DCD or not?

    RTS and DTR are outputs from the serial card, whilst...
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    The Service Manual for the 1701/1702 can be found...

    The Service Manual for the 1701/1702 can be found here: https://gona.mactar.hu/Commodore/monitor/schematics/1701-1702_Service_Manual_Preliminary_314004-001_(1984_Oct).pdf

    The manual contains the...
  18. I came across a similar issue with FORTRAN...

    I came across a similar issue with FORTRAN LOGICALs a few years ago.

    FORTRAN has .TRUE. and .FALSE. which generally equate to .FALSE. == 0 and .TRUE. anything else other than zero.

    However,...
  19. It might be interesting for others to know what...

    It might be interesting for others to know what you did wrong and how you fixed it - especially if the 8080 CPU test gave your emulation a 'clean bill of health'.

    This would indicate that the 8080...
  20. Thread: Mark 8 variant

    by daver2
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    >>> Well, things might not be what they look like...

    >>> Well, things might not be what they look like at first sight... Check this picture. Maybe you see what I mean :-).

    Yep, it's amazing what a bit of 'perspective' brings to the proceedings!
    ...
  21. BDOS is only used at one place - just after label...

    BDOS is only used at one place - just after label FINISH:. This can safely be removed...

    The CO and CI routines will require modification to talk to the correct serial port (in the same why that...
  22. Iíll check the source for the diagnostics...

    Iíll check the source for the diagnostics presently (when I fire up my laptop) and see what it does use.

    Apart from WARM BOOT and (perhaps) console I/O, and the odd reset drives BDOS call, I...
  23. Hi Marty, Well, since you have a way of...

    Hi Marty,

    Well, since you have a way of assembling John’s source code, why don’t you take a copy of ZFDCDIAG.Z80, delete the symbol BDOS, and modify the code so that it doesn’t require COM to...
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    No problem. Just wanted to make sure of...

    No problem.

    Just wanted to make sure of that...

    The rest of the tests are still valid though regarding the focus potentiometer.

    Dave
  25. Thread: Mark 8 variant

    by daver2
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    Looking at the hand-drawn 0-7 octal keyboard back...

    Looking at the hand-drawn 0-7 octal keyboard back in the posts that DOESN'T look like the one in the dg_packet at all.

    I would be interested in seeing what other "hand-drawn" schematics you...
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