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  • daver2's Avatar
    Today, 03:54 AM
    Welcome to VCFED - from across the pond! Dave
    6 replies | 94 view(s)
  • daver2's Avatar
    Yesterday, 02:55 PM
    I wouldn't get bogged down too much with how the circuit actually works at this point in time. The three ENn signals are used to decode which of...
    30 replies | 746 view(s)
  • daver2's Avatar
    Yesterday, 11:25 AM
    Ditto this side of the pond :-)! I think pretty much of the information you are looking for can be gleaned from the schematics for the 8/E and the...
    30 replies | 746 view(s)
  • daver2's Avatar
    Yesterday, 08:00 AM
    We've even got some snow in the UK too! The weather forecast is for a major snow storm tomorrow (Sunday) so that will bring the UK to a grinding...
    30 replies | 746 view(s)
  • daver2's Avatar
    December 8th, 2017, 01:55 PM
    Your schematic is much more readable than mine! You are thinking exactly the way I was (now I know what the pin identification is). My feeing...
    30 replies | 746 view(s)
  • daver2's Avatar
    December 8th, 2017, 07:34 AM
    Mike, Just thinking out loud here... The 'easy' way to resolve this issue is to slow the clock down really slow - or (even better) to single-cycle...
    30 replies | 746 view(s)
  • daver2's Avatar
    December 5th, 2017, 12:22 PM
    This looks like a Commodore SuperPET add-on card - but seems to be missing the DRAM and the 6702. The EPROMs look a bit 'lite' as well. An early...
    1 replies | 95 view(s)
  • daver2's Avatar
    December 5th, 2017, 11:42 AM
    daver2 replied to a thread Nascom in Other
    Yes, it does look to be a tasty combination of a NASCOM 2 and a series of GEMINI boards. Unfortunately, no AVC or PLUTO graphics card... Maybe I can...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 5th, 2017, 07:28 AM
    daver2 replied to a thread Another Nascom in Other
    LK3 = Not interested in. LK6 = 2 MHz CPU operation. LK4 = Not interested in. I assume this is a NASCOM 1 on its own (i.e. no buffer board or...
    5 replies | 194 view(s)
  • daver2's Avatar
    December 4th, 2017, 01:10 PM
    daver2 replied to a thread Another Nascom in Other
    The more the merrier Andy! So, it looks like you have a well-formed and synchronised 48 by 16 VDU display - which is good. What monitor ROM...
    5 replies | 194 view(s)
  • daver2's Avatar
    December 4th, 2017, 10:24 AM
    daver2 replied to a thread Nascom in Other
    >>> Is it supposed to be that... er.. snowy? Well, it is nearly Christmas... Without the "snow plough" or "snow dinger" modifications - YES! It...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 4th, 2017, 09:56 AM
    daver2 replied to a thread Nascom in Other
    You're being too kind Falter - it is interesting helping with the wide variety of equipment you keep buying... I am really impressed that you have...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 3rd, 2017, 10:53 AM
    daver2 replied to a thread Nascom in Other
    You'll just have to swap IC1 and see... Yep - I have a PDP-11/45 with a DEC TU56 tape drive that is essentially a 'retirement project' - but I am...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 3rd, 2017, 10:25 AM
    daver2 replied to a thread Nascom in Other
    IC5 also appears to be used on A0, A1, A2 and then A9, A10 and A11. I have just managed to track down a working copy of PROLOG for DEC's RT11...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 3rd, 2017, 10:09 AM
    daver2 replied to a thread Nascom in Other
    Address line A0 still seems to be permanently a '1'. Whatever you did seemed to fix the data error. The NASCOM is also upside down :-)! Dave
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 3rd, 2017, 09:54 AM
    daver2 replied to a thread Nascom in Other
    Yes, my code started at E000. E000 to E050 is fine. The first thing I see is an address fault with what looks like address line A0. You need to...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 3rd, 2017, 07:13 AM
    Yes, The software that runs on the computer is loaded off the floppy disk. The unit that plugs into the USER PORT is an interface to the external...
    7 replies | 224 view(s)
  • daver2's Avatar
    December 3rd, 2017, 06:28 AM
    daver2 replied to a thread Nascom in Other
    There are the RAM/EPROM chips themselves on the RAM-A card - but there are also 3 off 81LS97 buffers on the board for buffering the data bus. IC1...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 2nd, 2017, 03:11 PM
    daver2 replied to a thread Nascom in Other
    Oh well, nothing disasterous in the end. It is getting late in the UK and I need to go to bed! Can I suggest before doing anything else, you...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 2nd, 2017, 02:58 PM
    daver2 replied to a thread Nascom in Other
    Getting there slowly... What is the setting on LK1 - INT or EXT? It shouldn't matter whether the device was a 161 or a 163 in that position...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 2nd, 2017, 02:51 PM
    daver2 replied to a thread Nascom in Other
    Incidentally, you now should have a POWER ON RESET. The advances the buffer board made :-)! Dave
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 2nd, 2017, 02:45 PM
    daver2 replied to a thread Nascom in Other
    So, if memory and I/O link blocks are both set at INT the problem is going to be the clock - or there is another control line that is not connected...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 2nd, 2017, 01:59 PM
    daver2 replied to a thread Nascom in Other
    This happens to us all at times... Is IC46 pin 12 receiving the low-going reset pulse as well? Presumably, all you still have is the 'garbage...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 2nd, 2017, 01:35 PM
    daver2 replied to a thread Nascom in Other
    ??? I am looking at a picture and schematic of an ISSUE 2 buffer board... The buffer board schematic clearly shows a round pin 34 (which is the...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 2nd, 2017, 12:56 PM
    daver2 replied to a thread Nascom in Other
    The base of the transistor will only 'pulse' to 0.6V or so. You won't see that on your logic probe! So, if you can see a low-going pulse on one...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 2nd, 2017, 12:10 PM
    daver2 replied to a thread Nascom in Other
    collector - not emitter... The emitter should be connected to ground. The collector should be connected to one end of R7 (1k) (which, in turn,...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 2nd, 2017, 11:54 AM
    daver2 replied to a thread Nascom in Other
    Ok - is IC13 on the buffer board producing a high-going pulse on pin 5 when you press the reset button? If so, this pulse should go into the base...
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 2nd, 2017, 11:45 AM
    daver2 replied to a thread Nascom in Other
    OK. So the low-going RESET pulse should appear next on pin 34 of the 43-way N1 edge connector. Dave
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 2nd, 2017, 11:28 AM
    daver2 replied to a thread Nascom in Other
    Ah, that'll be that then... Dave
    181 replies | 4364 view(s)
  • daver2's Avatar
    December 2nd, 2017, 11:18 AM
    daver2 replied to a thread Nascom in Other
    Which way are you counting pin 10 of NASBUS on the buffer board out of interest? The KEYWAY is pin 72 - so it is the opposite side of the buffer...
    181 replies | 4364 view(s)
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SW/HW design engineer

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