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  • daver2's Avatar
    Today, 04:08 AM
    daver2 replied to a thread Nascom in Other
    I can see some video signals :-). Pin 1 of the 3-way additional socket is connected to an LED. There are two LEDs on the N1. One indicates CPU...
    38 replies | 1023 view(s)
  • daver2's Avatar
    Yesterday, 10:00 AM
    daver2 replied to a thread DEC register 8271 in DEC
    Pretty much the only thing that is required for the PDP-8 architecture are registers, an adder, a shifter and some selection gates (also effectively...
    8 replies | 198 view(s)
  • daver2's Avatar
    Yesterday, 08:37 AM
    daver2 replied to a thread Nascom in Other
    Yes, I saw some 'random' connectors that have been added without labels (one of my pet hates). The problem with stripping the wires off is if any...
    38 replies | 1023 view(s)
  • daver2's Avatar
    Yesterday, 04:34 AM
    daver2 replied to a thread Nascom in Other
    The components that are missing are associated with the RF signal output. Therefore, only the composite video signal will work. If nothing is...
    38 replies | 1023 view(s)
  • daver2's Avatar
    Yesterday, 02:53 AM
    daver2 replied to a thread Nascom in Other
    Just been having a look at your GDrive hi-res pictures and I can't see anything wired to either the top or the bottom of the board for composite...
    38 replies | 1023 view(s)
  • daver2's Avatar
    Yesterday, 02:31 AM
    daver2 replied to a thread Nascom in Other
    Your 'friend' is the NASCOM 1 construction manual... http://www.nascomhomepage.com/pdf/N1HM.PDF. Page -28- details the 'default' link configurations...
    38 replies | 1023 view(s)
  • daver2's Avatar
    November 17th, 2017, 03:42 PM
    They are fairly rare - but they do come up for sale occasionally. They then can go for 'silly' money! Round about 500-600 is they typical value...
    53 replies | 9952 view(s)
  • daver2's Avatar
    November 17th, 2017, 02:22 PM
    daver2 replied to a thread Nascom in Other
    He He... To be honest, bugg*r board does actually sum it up quite nicely! I would guess that your NASCOM 1 gets its power from the NASBUS...
    38 replies | 1023 view(s)
  • daver2's Avatar
    November 17th, 2017, 12:22 PM
    daver2 replied to a thread Nascom in Other
    Excellent photographs. I would ignore the other two transformers for now as (a) they don't appear to be connected to anything and (b) they don't...
    38 replies | 1023 view(s)
  • daver2's Avatar
    November 17th, 2017, 10:49 AM
    daver2 replied to a thread Nascom in Other
    Hi Falter, Funnily enough, I was just about to post you... Give me a minute or two! The first place to start is the NASCOM 3A power supply PCB...
    38 replies | 1023 view(s)
  • daver2's Avatar
    November 16th, 2017, 11:43 AM
    daver2 replied to a thread Saving ROM data from Tek 4052 in Other
    >>> I agree with your annotations. Excellent, so the first hurdle over with! >>> Why is memory only checked up to FEEA, when RAM ends at FEFF...
    91 replies | 6931 view(s)
  • daver2's Avatar
    November 13th, 2017, 11:38 PM
    The Z80 is a bit strange in this respect... It may be static in nature (or 'leaky' as Chuck states) - but the CPU contained DRAM refresh logic. Of...
    12 replies | 352 view(s)
  • daver2's Avatar
    November 13th, 2017, 01:58 PM
    A 'static' CPU stores the internal state (e.g. Register values) in a cross-coupled flip-flop arrangement for each bit. The contents of the resulting...
    12 replies | 352 view(s)
  • daver2's Avatar
    November 13th, 2017, 06:06 AM
    daver2 replied to a thread Saving ROM data from Tek 4052 in Other
    >>> It's not clear from the manual, but I think this address space may be statically reserved for external ROMs from the outset, rather than...
    91 replies | 6931 view(s)
  • daver2's Avatar
    November 12th, 2017, 11:14 AM
    daver2 replied to a thread Saving ROM data from Tek 4052 in Other
    Thanks. It has been a pretty interesting couple of days (although my wife would have a different word for it other than interesting...) Sorry I...
    91 replies | 6931 view(s)
  • daver2's Avatar
    November 12th, 2017, 09:03 AM
    daver2 replied to a thread Saving ROM data from Tek 4052 in Other
    Your post finally escaped from the mods... Actually, you may be OK now from the number of posts that I see you have made. As you can see, I am...
    91 replies | 6931 view(s)
  • daver2's Avatar
    November 12th, 2017, 04:20 AM
    daver2 replied to a thread Saving ROM data from Tek 4052 in Other
    I was perusing my ROM dump this morning and found - almost at the end of the CONSTANT ROM - a couple of references to 79F3 (what we think is the...
    91 replies | 6931 view(s)
  • daver2's Avatar
    November 11th, 2017, 12:35 PM
    daver2 replied to a thread Saving ROM data from Tek 4052 in Other
    I have been having a look at the address decoding in a bit more depth. This is what I have deduced (which may require me to change my memory dump...
    91 replies | 6931 view(s)
  • daver2's Avatar
    November 11th, 2017, 12:11 PM
    daver2 replied to a thread Saving ROM data from Tek 4052 in Other
    OK - I'm back on the case (for a short while at least)... I have 'reassembled' the ROMS and dumped them out in both HEX and ASCII. Note that I...
    91 replies | 6931 view(s)
  • daver2's Avatar
    November 8th, 2017, 09:48 AM
    CP/M 3 supports bank switched RAM. The bank switching is used from 0000 upwards, with the higher locations as non-switched 'common' memory. This...
    66 replies | 2788 view(s)
  • daver2's Avatar
    November 7th, 2017, 01:27 PM
    I am a little busy this week - but hopefully I will find some time at the weekend. By 'run out of stack space' - if I remember correctly, CP/M...
    66 replies | 2788 view(s)
  • daver2's Avatar
    November 6th, 2017, 12:43 PM
    daver2 replied to a thread Saving ROM data from Tek 4052 in Other
    Hi GT, Many apologies... Having re-read the posts - I have suddenly realised that I failed to pick up the new set of ROM images that you had...
    91 replies | 6931 view(s)
  • daver2's Avatar
    November 6th, 2017, 08:41 AM
    The most obvious technique is one that the original software author should have adopted - that of writing comments in their code! I used to write...
    8 replies | 306 view(s)
  • daver2's Avatar
    November 5th, 2017, 02:08 PM
    Can you post a photograph of the underside of the PCB and let us know what the part number is for the 14-pin chip. We should be able to identify...
    11 replies | 347 view(s)
  • daver2's Avatar
    November 5th, 2017, 01:35 PM
    A similar thing to the C68160 has come up before (see http://www.vcfed.org/forum/showthread.php?40432-PET-4016-with-substituted-characters/page2 -...
    11 replies | 347 view(s)
  • daver2's Avatar
    November 5th, 2017, 11:27 AM
    Yep, assembly language programming sorts the men out from the boys! Although, from what I've seen, you have picked up Z80 assembly language pretty...
    66 replies | 2788 view(s)
  • daver2's Avatar
    November 5th, 2017, 11:17 AM
    daver2 replied to a thread BBC Micro Model B in Other
    Well done that man. Yes, the keyboard is very nice on the BEEB. You will also find the keyboard on the NASCOM nice as well. FYI you can buy...
    23 replies | 730 view(s)
  • daver2's Avatar
    November 5th, 2017, 09:57 AM
    Looking back through a previous post (number 33) - GETFROMCHARB 'zaps' HL - so you have just loaded HL from (MEM_TGT) called GETFROMCHARB (which has...
    66 replies | 2788 view(s)
  • daver2's Avatar
    November 5th, 2017, 09:49 AM
    Ah... So, if the '#' is your EOL then I can see why the CR/LF is not output - because your code checks for EOL and branches directly to label...
    66 replies | 2788 view(s)
  • daver2's Avatar
    November 5th, 2017, 07:15 AM
    The difficult bugs are always the best! Think of it all as a learning opportunity... Point 1: The output in the second code block was not produced...
    66 replies | 2788 view(s)
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SW/HW design engineer

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