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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 4th Jul 2021, 4:52 am   #41
Mark1960
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Default Re: Multiprocessing SCMPII on MK14

Quote:
Originally Posted by SiriusHardware View Post
When trying to convert some of the listings in the MK14 manual to SBASM3 format I discovered that some would not directly assemble, or would not reproduce the original hex code verbatim, because of errors. There was a strong feeling that the programs in the manual had never been within sight of an actual assembler and had instead been hand-assembled and typed.
Its also possible that errors were caused by typesetting. The listing doesn’t show the slightly off alignment that would be expected if printed on a line printer or the dots that would show on a dot matrix printer. It also looks too good for a daisywheel or golfball printer.
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Old 4th Jul 2021, 9:30 am   #42
Slothie
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Default Re: Multiprocessing SCMPII on MK14

Quote:
Originally Posted by Mark1960 View Post
Quote:
Originally Posted by SiriusHardware View Post
When trying to convert some of the listings in the MK14 manual to SBASM3 format I discovered that some would not directly assemble, or would not reproduce the original hex code verbatim, because of errors. There was a strong feeling that the programs in the manual had never been within sight of an actual assembler and had instead been hand-assembled and typed.
Its also possible that errors were caused by typesetting. The listing doesn’t show the slightly off alignment that would be expected if printed on a line printer or the dots that would show on a dot matrix printer. It also looks too good for a daisywheel or golfball printer.
The listings look like they have been typeset by someone with a listing, as errors where they occur often are similar looking digits (8 and B, 'O' and 0 etc) This was a common problem with listings in magazines until they started putting in scans of matrix printer output.
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Old 6th Jul 2021, 1:07 am   #43
Mark1960
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Default Re: Multiprocessing SCMPII on MK14

Problem was due to the wrong crystal fitted. I had a 7.3728MHz fitted instead of 4.4316MHz. The setup time for address to NADS falling edge is dependent on the clock. Tc/2 -150 ns. At the higher frequency its just on the edge of the data setup time for the 74LS395 to the falling edge on NADS. Capacitance from a finger or scope probe is enough of a delay for it to work.

If I’m going to try and overclock the processors I should probably change to a positive edge triggered register or a transparent latch.
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Old 6th Jul 2021, 11:09 pm   #44
Mark1960
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Default Re: Multiprocessing SCMPII on MK14

Just thinking about possible replacements of the 74ls395.

74ls163 is a possible. This is quite close to the pinout of the 74ls395 and might only need a simple mod to the wiring. The 74ls163 is a counter, but could be used as a latch if load input is held low and this would latch data on the rising edge at the end of NADS. There is still plenty of time in the rest of the bus cycle for any modern sram even with the scmp running at double the clock frequency.

74ls173 is also a good possibility, though the wiring mod is a bit more involved. The 74ls173 is also rising edge triggered but also has the advantage of a positive logic reset input, which could be driven by NENIN so the ortonview or mk14 vdu would force page 0. I also have the option of 74hct173 to reduce the load on the data bus.

74ls193 would give active low gated transparent latch with positive logic reset, though I don’t think I have any. I might have 74ls192 and although this is a bcd type I think that would only make a difference if the count function was used.
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