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  • daver2's Avatar
    January 27th, 2020, 10:58 PM
    Hi Monty, Certainly knowing the correct ‘order’ in which the microcode is executed would be extremely useful. I am both trying to work out how the...
    3 replies | 62 view(s)
  • daver2's Avatar
    January 27th, 2020, 09:50 AM
    >>> Unless Dave can get his 4052 emulator working - hint, hint. KILL BIRD :-)! Nice work! I will be taking long weekends until the end if...
    3 replies | 62 view(s)
  • daver2's Avatar
    January 26th, 2020, 01:02 PM
    No problem. Just a thought... With the power off (and everything discharged) you could just check around with your multimeter on resistance and...
    6 replies | 107 view(s)
  • daver2's Avatar
    January 26th, 2020, 03:58 AM
    Bit of time to have a look at your problem between Church and lunch... Yes, welcome back to the Commodore thread... R752 feeds the +400V...
    6 replies | 107 view(s)
  • daver2's Avatar
    January 26th, 2020, 12:54 AM
    Yes, there are two ‘massive’ threads already on this topic. Can I suggest looking them up and seeing if anything looks familiar with your PET...
    6 replies | 107 view(s)
  • daver2's Avatar
    January 26th, 2020, 12:43 AM
    daver2 replied to a thread PET 2001 Issues in Commodore
    So your Uncle’s machine has a duff 6520. Yes, shop around and don’t pay the daft prices! You should be able to pick up a 6520 for £5 ish. I am over...
    21 replies | 223 view(s)
  • daver2's Avatar
    January 25th, 2020, 01:12 PM
    daver2 replied to a thread PET 2001 Issues in Commodore
    The 2001 is the ‘original’ PET. There are a number of mainboard variants, but the main feature is static RAM. The 2001N is the ‘next generation’...
    21 replies | 223 view(s)
  • daver2's Avatar
    January 25th, 2020, 11:57 AM
    daver2 replied to a thread PET 2001 Issues in Commodore
    Ah, so that makes it a 2001N. The IEEE 488 6520 in this case is UC6 and the KEYBOARD/DIAG 6520 is UC7. Dave linked to the correct place back in...
    21 replies | 223 view(s)
  • daver2's Avatar
    January 25th, 2020, 11:06 AM
    daver2 replied to a thread PET 2001 Issues in Commodore
    Good point. 2001, 2001N, ... Dave
    21 replies | 223 view(s)
  • daver2's Avatar
    January 25th, 2020, 10:20 AM
    daver2 replied to a thread PET 2001 Issues in Commodore
    Yes, on the schematics the ‘U’ is missing. Sometimes I put it on, sometimes I don’t... They should both be 40 pin devices and both identified as...
    21 replies | 223 view(s)
  • daver2's Avatar
    January 25th, 2020, 08:44 AM
    daver2 replied to a thread PET 2001 Issues in Commodore
    I am ‘taking a flyer’ here and would say the 6520 PIA at G8 is possibly faulty. You could try swapping G8 and B8 over (assuming they are in...
    21 replies | 223 view(s)
  • daver2's Avatar
    January 25th, 2020, 07:49 AM
    daver2 replied to a thread SoC MK14 in Other
    Yes, This wasn’t a problem with the monitor code, it was a problem with the hardware design. The original hardware design enabled the interrupt...
    14 replies | 420 view(s)
  • daver2's Avatar
    January 22nd, 2020, 03:42 AM
    daver2 replied to a thread No serial output on PDP-11 in DEC
    Yes, If you have a 24 MHz set of probes connected to your logic analyser (and it is capable of resolving to this) then you should be able to...
    28 replies | 876 view(s)
  • daver2's Avatar
    January 21st, 2020, 01:16 PM
    Asm80 didn’t generate different code for the same source code. You told it to assemble two slightly different programs... I specified one in...
    53 replies | 2937 view(s)
  • daver2's Avatar
    January 19th, 2020, 11:12 AM
    It didn’t sound like that when I played it on the recorder... Perhaps a bit more work required on the audio front! Good quality video though. ...
    35 replies | 1869 view(s)
  • daver2's Avatar
    January 19th, 2020, 12:00 AM
    daver2 replied to a thread No serial output on PDP-11 in DEC
    So, something is running on the bus that the SIO is connected to... Have you got the means to check if pins 35 and 36 go LOW simultaneously (e.g....
    28 replies | 876 view(s)
  • daver2's Avatar
    January 18th, 2020, 01:25 PM
    daver2 replied to a thread No serial output on PDP-11 in DEC
    You can also look for activity on the following pins: 35 = /CE (must be low to select the SIO). 36 = /IORQ (must be low to select the SIO). 32 =...
    28 replies | 876 view(s)
  • daver2's Avatar
    January 18th, 2020, 12:51 PM
    daver2 replied to a thread No serial output on PDP-11 in DEC
    See my previous post #2 regarding CTS and the transmit and receive clocks. Dave
    28 replies | 876 view(s)
  • daver2's Avatar
    January 18th, 2020, 11:47 AM
    daver2 replied to a thread No serial output on PDP-11 in DEC
    Always worth a shot! Unfortunately, I think you are just going to have to do some 'computer archeology' and try and track down someone who knows...
    28 replies | 876 view(s)
  • daver2's Avatar
    January 18th, 2020, 11:20 AM
    daver2 replied to a thread No serial output on PDP-11 in DEC
    Thanks, I am starting to remember this now... The chips on those boards look like this is a heavily bespoke system (i.e. it is not a general...
    28 replies | 876 view(s)
  • daver2's Avatar
    January 18th, 2020, 09:27 AM
    daver2 replied to a thread No serial output on PDP-11 in DEC
    What on earth have you got there? The TMS9937 is a single chip video controller! I also see you have two (2) Z80 SIO chips - so what makes you...
    28 replies | 876 view(s)
  • daver2's Avatar
    January 17th, 2020, 01:29 AM
    daver2 replied to a thread No serial output on PDP-11 in DEC
    What about Clear to Send? Are you looping back Request To Send to Clear To Send? PDP-11 stuff generally doesn't use these lines - but this uses a...
    28 replies | 876 view(s)
  • daver2's Avatar
    January 15th, 2020, 03:00 PM
    daver2 replied to a thread Osi c4p in Other
    The best way is to learn to clear the screen (video and colour memory) and setup colour mode. Write your own subroutine and call that at the start of...
    103 replies | 3322 view(s)
  • daver2's Avatar
    January 15th, 2020, 01:00 AM
    daver2 replied to a thread SoC MK14 in Other
    What, A NASCOM 1 and now an MK14 :-)! Your British computer collection is expanding... >>> Yes I've heard some uncomplimentary things about the...
    14 replies | 420 view(s)
  • daver2's Avatar
    January 14th, 2020, 03:16 AM
    daver2 replied to a thread Osi c4p in Other
    >>> This is all making sense except for the angles thing Nope, nothing to do with the CRT at all... It is just a different way of describing...
    103 replies | 3322 view(s)
  • daver2's Avatar
    January 13th, 2020, 01:26 PM
    daver2 replied to a thread Osi c4p in Other
    It's more likely that there are so many manual adjustment potentiometers that getting it adjusted correctly is a nightmare :-)! You have digital...
    103 replies | 3322 view(s)
  • daver2's Avatar
    January 13th, 2020, 01:02 PM
    daver2 replied to a thread Osi c4p in Other
    Just had another thought whilst looking at the schematics and Terry's website. There are various components that should be removed if the OSI is...
    103 replies | 3322 view(s)
  • daver2's Avatar
    January 13th, 2020, 12:49 PM
    daver2 replied to a thread Osi c4p in Other
    You can have a colour on black or black on a colour. That's it... You can't have two colours in a particular character position. The pixels are...
    103 replies | 3322 view(s)
  • daver2's Avatar
    January 12th, 2020, 11:44 AM
    daver2 replied to a thread Osi c4p in Other
    >>> Hope your business trip was more exciting than my non-business trip here. The beatings will continue... I have just edited my post to...
    103 replies | 3322 view(s)
  • daver2's Avatar
    January 12th, 2020, 10:48 AM
    daver2 replied to a thread Osi c4p in Other
    Ready for the next instalment? Look at the schematic on page 6 of 8 of http://www.osiweb.org/manuals/OSI-540B.pdf. With the colour disabled...
    103 replies | 3322 view(s)
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