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  • daver2's Avatar
    Yesterday, 04:05 PM
    >>> The Z80 was used in millions of CP/M computers. So it looks like an oddity for me that there is still no any CP/M version optimized for the...
    14 replies | 128 view(s)
  • daver2's Avatar
    Yesterday, 12:15 AM
    daver2 replied to a thread Vintage years. in General Off Topic
    I sat on our company's Y2k committee and the numbers of equipment that failed the tests that we required for operation of our plant was quite large....
    7 replies | 126 view(s)
  • daver2's Avatar
    March 17th, 2019, 03:52 AM
    Hi Rob, Yes, I have learnt the hard way a few times that for a long or complex post you are better off editing your post outside of VCFED then...
    154 replies | 34060 view(s)
  • daver2's Avatar
    March 16th, 2019, 03:26 PM
    daver2 replied to a thread Nascom in Other
    I'll catch up with your posts tomorrow. Yes, the NASCOM 1 suffered from contention when accessing the video RAM at high speed (as you are doing)....
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 16th, 2019, 09:09 AM
    daver2 replied to a thread Nascom in Other
    Very interesting Mr. Spock... Having the 74S04 installed in IC9 is another modification to alleviate memory plague. I therefore suspect that...
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 16th, 2019, 05:34 AM
    daver2 replied to a thread Nascom in Other
    Thanks for the vote of confidence Ziloo... Yes, that part of the movie was an absolute classic moment! Debugging computer systems used to be my...
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 16th, 2019, 04:56 AM
    Well done, I was just thinking this morning on my walk that I hadn't heard back from you in a while. So, it was most likely the original and...
    77 replies | 4175 view(s)
  • daver2's Avatar
    March 16th, 2019, 04:16 AM
    daver2 replied to a thread Nascom in Other
    So, I can't see anything physically wrong with your RAM 'A' card scans. The 8K ROM BASIC upgrade seems to follow that as described - with the...
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 15th, 2019, 03:26 PM
    daver2 replied to a thread Nascom in Other
    I thought you were a bit quiet today... No problem, you need to prioritise your work! It is a good idea to scan the cards though. I have had a...
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 15th, 2019, 07:43 AM
    daver2 replied to a thread Nascom in Other
    The next thing to look at is the 4K and 16K decode logic on the RAM board. To do this, enter a very small program into memory via NAS-SYS and...
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 15th, 2019, 07:20 AM
    daver2 replied to a thread Nascom in Other
    Ok, so I have reacquainted myself with the schematics. The problem is unlikely to be the 81LS97s on the RAM board. The ROM and RAM have separate...
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 14th, 2019, 01:07 PM
    daver2 replied to a thread Nascom in Other
    81LS95 vs 81LS97 device. The 81LS97 is a dual 4-bit tristate buffer. It has two active low enable pins. Pin 1 enables the first half of the...
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 14th, 2019, 10:51 AM
    On a project I am currently working on - we have some wire-wrap configuration posts on one of the cards we are remanufacturing. The PCB assembly firm...
    154 replies | 34060 view(s)
  • daver2's Avatar
    March 14th, 2019, 08:23 AM
    daver2 replied to a thread Nascom in Other
    The 7402 is associated with the address decoding for the BASIC ROM. Thanks for the photographs - the wire links make complete sense to me - although...
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 12th, 2019, 08:42 AM
    Ditto for me. Dave
    16 replies | 391 view(s)
  • daver2's Avatar
    March 12th, 2019, 08:39 AM
    daver2 replied to a thread Nascom in Other
    Page 12 of https://80bus.co.uk.mirror.jloh.de/publications/magazines/INMC_news_5.pdf#page=13 describes the RAM A modification to add the 8K ROM BASIC...
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 12th, 2019, 08:27 AM
    daver2 replied to a thread Nascom in Other
    Documentation at https://80bus.co.uk.mirror.jloh.de/pages/nascom/rama.htm. Yes, there was a 'bodge' to convert one of the 1K EPROM sockets to...
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 12th, 2019, 07:12 AM
    daver2 replied to a thread Nascom in Other
    Thanks. So the first thing I would look for is the 4K block address decode logic implemented by the RAM A card. I haven't got access to the...
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 12th, 2019, 01:45 AM
    daver2 replied to a thread Nascom in Other
    So when you say the NASCOM is 'losing' much of its available RAM, what do you mean? If you have RAM up to $0FFF - then this is the on-board SRAM. I...
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 9th, 2019, 12:02 PM
    daver2 replied to a thread Nascom in Other
    If C17 is broken - I would replace it. It is in the cassette demodulator circuit. I don't think it has a major function to play - but just in case......
    223 replies | 15423 view(s)
  • daver2's Avatar
    March 9th, 2019, 11:52 AM
    daver2 replied to a thread DECtapes on Ebay. in DEC
    And that's exactly what the German to English translation says as well... Dave
    2 replies | 178 view(s)
  • daver2's Avatar
    March 8th, 2019, 01:40 PM
    daver2 replied to a thread Nascom bad again in Other
    IC2 should NOT be enabled if nothing is plugged into the external NASBUS. Either you have a faulty 81LS95 or something driving it is faulty. What...
    10 replies | 397 view(s)
  • daver2's Avatar
    March 8th, 2019, 07:14 AM
    daver2 replied to a thread PDP-11/10 with TU60 on Ebay. in DEC
    Just thinking the same myself - although shipping to the UK will be somewhat prohibitivly expensive! Dave
    7 replies | 304 view(s)
  • daver2's Avatar
    March 7th, 2019, 01:32 PM
    daver2 replied to a thread Nascom bad again in Other
    This is the info I have found on the Nascom 1 buffer board: https://nascom.wordpress.com/nascom/hardware/nascom-1-2/buffer-board/ >>> Really wish...
    10 replies | 397 view(s)
  • daver2's Avatar
    March 6th, 2019, 10:14 PM
    XON/XOFF support should be bidirectional. A remote multiuser computer could be 'busy' performing other tasks and could initiate an XOFF itself under...
    2 replies | 163 view(s)
  • daver2's Avatar
    March 5th, 2019, 10:55 AM
    Download the data sheet for the part... For example, The 'D' package suffix from Texas Instruments is not a DIP package, so it physically won't...
    4 replies | 202 view(s)
  • daver2's Avatar
    March 5th, 2019, 08:32 AM
    daver2 replied to a thread D.R.E.A.M. 6800 Build in Other
    I have just placed an order for 5 off DREAM 6800 cards (40th anniversary revamp edition) as identified back in my post #35 from one of the Chinese...
    61 replies | 4056 view(s)
  • daver2's Avatar
    March 4th, 2019, 12:36 PM
    daver2 replied to a thread Nascom bad again in Other
    Yes, you are spot on with the clock! I see the buffer board should also have a power-on reset, so I am not sure why you are having to manually...
    10 replies | 397 view(s)
  • daver2's Avatar
    March 4th, 2019, 10:55 AM
    daver2 replied to a thread Nascom bad again in Other
    It looks like the video sub-system is working fine - so that probably rules out the clock etc. I would go for the NAS-SYS ROM/EPROM or the RAM. ...
    10 replies | 397 view(s)
  • daver2's Avatar
    February 23rd, 2019, 12:26 PM
    daver2 replied to a thread Heathkit ET6800 in Other
    Nothing found specifically about the Heathkit ET6800 - but plenty on the ET-3400 over at...
    4 replies | 307 view(s)
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About daver2

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About daver2
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SW/HW design engineer

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