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  • daver2's Avatar
    Today, 12:36 AM
    daver2 replied to a thread Nascom in Other
    You're up early this morning?! The important things are INT for memory (got that one covered) and the CPU clock to 2 MHz. Don't bother about the...
    53 replies | 1246 view(s)
  • daver2's Avatar
    Yesterday, 11:41 PM
    daver2 replied to a thread Nascom in Other
    I don't think that's a bad Sunday's work actually!!! The video picture looks about right (although it is not quite centred or synced on the screen...
    53 replies | 1246 view(s)
  • daver2's Avatar
    Yesterday, 11:27 AM
    daver2 replied to a thread Nascom in Other
    Returning to 'stock' would be a solution. Ideally, you want to do a full PCB check for cut tracks as these are the things that will catch you out. ...
    53 replies | 1246 view(s)
  • daver2's Avatar
    Yesterday, 09:58 AM
    daver2 replied to a thread Nascom in Other
    LK1 to INTERNAL means that the N1 performs its own I/O block decode and you can't add any I/O devices onto NASBUS. That's OK for the moment...
    53 replies | 1246 view(s)
  • daver2's Avatar
    Yesterday, 07:05 AM
    daver2 replied to a thread Saving ROM data from Tek 4052 in Other
    I have done a bit of disassembly on what I think are the interrupt handler routines. I haven't got time to write up my hand-written notes just yet...
    92 replies | 6989 view(s)
  • daver2's Avatar
    Yesterday, 06:17 AM
    daver2 replied to a thread Nascom in Other
    Broken Wire #1 = 'common' point of LK4 = TX/RX clock to UART. Broken Wire #2 - Pin 40 of UART (you state) which is the same as the above? ...
    53 replies | 1246 view(s)
  • daver2's Avatar
    Yesterday, 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...
    53 replies | 1246 view(s)
  • daver2's Avatar
    November 18th, 2017, 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...
    9 replies | 248 view(s)
  • daver2's Avatar
    November 18th, 2017, 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...
    53 replies | 1246 view(s)
  • daver2's Avatar
    November 18th, 2017, 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...
    53 replies | 1246 view(s)
  • daver2's Avatar
    November 18th, 2017, 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...
    53 replies | 1246 view(s)
  • daver2's Avatar
    November 18th, 2017, 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...
    53 replies | 1246 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 | 9996 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...
    53 replies | 1246 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...
    53 replies | 1246 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...
    53 replies | 1246 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...
    92 replies | 6989 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 | 354 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 | 354 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...
    92 replies | 6989 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...
    92 replies | 6989 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...
    92 replies | 6989 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...
    92 replies | 6989 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...
    92 replies | 6989 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...
    92 replies | 6989 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 | 2809 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 | 2809 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...
    92 replies | 6989 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 | 311 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)
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SW/HW design engineer

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