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Old 18th Nov 2022, 12:23 pm   #21
SiriusHardware
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Default Re: Unbuilt original MK14 VDU

Quote:
please change the 74L86 to 74LS86
In addition to Mark's plea above I would like to suggest making provision for a resistor in series with the TOP PAGE output to stop it from being damaged by (or damaging) any other active output which it may be accidentally connected to.

You could probably lose the modulator and convert the output circuit to a 75R composite video buffer as well, since people are more likely to use / need that type of connection.
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Old 18th Nov 2022, 8:03 pm   #22
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Default Re: Unbuilt original MK14 VDU

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Originally Posted by SiriusHardware View Post
Quote:
please change the 74L86 to 74LS86
You could probably lose the modulator and convert the output circuit to a 75R composite video buffer as well, since people are more likely to use / need that type of connection.
Perhaps a component layout under the space for a modulator to allow an alternate fit for those who want the look - or even just as is done on other machines hollow out the Modulator to be the composite just soldered to a different hole next to the one suitable for the modulator.
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Old 18th Nov 2022, 9:41 pm   #23
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Default Re: Unbuilt original MK14 VDU

That would involve vandalising a 40+ year old modulator although it is reversible if carefully done (and indeed is commonly done). Great idea to put the trackwork for the components for composite-out entirely within the outline which would be occupied by the modulator though. By the same token you could also put the TOP PAGE series resistor in the hollow between the sides of one of the IC sockets so that it would be hidden when the IC and socket were fitted.
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Old 9th Dec 2022, 8:41 pm   #24
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Default Re: Unbuilt original MK14 VDU

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Originally Posted by Mark1960 View Post

Timbucus has a replica of the SoC vdu, I think from a guy called Martin in Czech republic. I don’t know if they are still available.
Martin still has boards available and I received mine today.
It is a nearly exact copy of the original and the IC leg holes and about 95% of the vias perfectly line up if you hold the boards together.

The attached photo shows the original on the left and the reproduction on the right

https://www.8bity.cz/2018/mk14-vdu-v...-unit-replica/
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Old 9th Dec 2022, 9:41 pm   #25
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Default Re: Unbuilt original MK14 VDU

Thanks for letting us know - as a matter of interest do you know if Martin still has full kits available? Not asking for myself of course but I remember that all you needed was the PCB, others may still.be interested in complete kits.
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Old 9th Dec 2022, 10:28 pm   #26
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Default Re: Unbuilt original MK14 VDU

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Originally Posted by SiriusHardware View Post
Thanks for letting us know - as a matter of interest do you know if Martin still has full kits available? Not asking for myself of course but I remember that all you needed was the PCB, others may still.be interested in complete kits.
The list he sent was PCBs for all his designs: MK14/VDU/Cassette/ROMRAM plus switches, foils and PROMS for his MK14 board.
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Old 10th Dec 2022, 2:43 pm   #27
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Default Re: Unbuilt original MK14 VDU

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Martin still has boards available and I received mine today.
Is there a link to a sales page on Martin's site (I couldn't find one) or did you mail him directly?
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Old 10th Dec 2022, 10:04 pm   #28
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Default Re: Unbuilt original MK14 VDU

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Is there a link to a sales page on Martin's site (I couldn't find one) or did you mail him directly?
I emailed him directly using the email address on the contacts page.
(View that page in the original czech language as the translator messes the email address up a bit)
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Old 2nd Jan 2023, 6:33 am   #29
Brian of Romsey
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Default Re: Unbuilt original MK14 VDU

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It's just a pity that SOC didn't go with a 4.00 MHz crystal in the first place but of course the reason they didn't is that 4.43MHz ones were abundant and cheap due to their widespread use in colour TVs at that time.

As you say the change to a 4.00MHz crystal does have consequences for some of the example programs from the manual such as 'digital clock' and 'music box' which were both written with software timing dependent on the original clock frequency, so if it is possible to retain the 4.43MHz crystal and use the VDU, so much the better.
So are SC/MP II CPUs reliable at almost 11% overclocked? Has anyone gone to extremes to see what the chips are capable of? I guess you'd need to have moved to a UART or an ACIA for the terminal or your baud rate would get shot to hell.
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Old 2nd Jan 2023, 8:36 am   #30
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Default Re: Unbuilt original MK14 VDU

11% overclocked is not even close to the maximum.

I have been able to run a few samples at 9 MHz in Slothie’s issue VI replica running the SoC monitor. I didn’t find one that wouldn’t run at 8 MHz. If you are latching the upper address bits then you need to latch on the rising edge of NADS or use a transparent latch. I’d recommend 74hct193.
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Old 2nd Jan 2023, 7:25 pm   #31
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Default Re: Unbuilt original MK14 VDU

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So are SC/MP II CPUs reliable at almost 11% overclocked?
We have to imagine so as 4.43MHz was the standard crystal supplied with the MK14 kit, because, you can probably guess, they were widely available (therefore very cheap) due to their widespread use in PAL colour TVs at the time.

As Mark said, though, he has had his cranked up to quite a bit higher...
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Old 3rd Jan 2023, 2:32 pm   #32
Brian of Romsey
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Default Re: Unbuilt original MK14 VDU

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Originally Posted by Mark1960 View Post
11% overclocked is not even close to the maximum.

I have been able to run a few samples at 9 MHz in Slothie’s issue VI replica running the SoC monitor. I didn’t find one that wouldn’t run at 8 MHz. If you are latching the upper address bits then you need to latch on the rising edge of NADS or use a transparent latch. I’d recommend 74HCT193.
OK, looks like I definitely need to separate the CPU clock and the baud rate clock. I'm going with 7.3728 MHz from a DIP oscillator divided down using a 74LS74 for the baud rate clock. I have a load of NS16450N which don't have a FIFO but are capable of being upgraded to 16550A (or later) if this is an issue. Any comments on the possibility of Rx overrun because the likes of FTDI chips don't stop immediately upon getting RTS (or is that CTS) de-asserted?

At 8 MHz we might get some processing done . Does cooling or fooling about with Vcc help much?

I was planning to use either 'LS573 or 'LS574. In this particular case there didn't seem to be much difference in the outcome for A12..15. (I'm choosing LS because they are already on hand.) One has to invert NADS either way.

Planning on a Dallas DS1233-5 for the NRST line so it can be driven from the bus side if needs be.

Thanks, Brian.
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Old 3rd Jan 2023, 6:05 pm   #33
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Default Re: Unbuilt original MK14 VDU

Just run the sc/mp at 7.3728 MHz

Use the 573 if thats the only choice between 573 or 574.

193 doesn’t need to invert NADS. 192 would probably also work. Ground the clock inputs to disable counting and you can also use the carry and borrow outputs as decoded 4k address pages for IO or ROM.
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Old 4th Jan 2023, 9:00 am   #34
Brian of Romsey
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Default Re: Unbuilt original MK14 VDU

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Just run the sc/mp at 7.3728 MHz

Use the 573 if thats the only choice between 573 or 574.

193 doesn’t need to invert NADS. 192 would probably also work. Ground the clock inputs to disable counting and you can also use the carry and borrow outputs as decoded 4k address pages for IO or ROM.
I've given the 'HCT193 datasheet some study and indeed it is an elegant solution to latching A12..15 from the leading (falling) edge of NADS. I really like the idea of using NTCU and NTCD as decodes for page 0 and page F, that's clever. I'm hoping that my GAL will sweep up the inversion of NADS to let the '73 go transparent or to clock the '74 from the leading edge of NADS. I looked at the required setup and hold times and there's heaps of leeway (might have to do that again if I can run the CPU at 8 or 9 MHz).

Indeed, running at 7.3728 MHz will be fine for initial testing, with jumper options for 3.6864 MHz and 1.8432 MHz as well. Maybe swap the 'LS74 for a 'HC393 with a 'HCT14 for level translation from the can oscillator. More stages, more flexibility.
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Old 4th Jan 2023, 12:07 pm   #35
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Default Re: Unbuilt original MK14 VDU

Now thats clever, I hadnt seen the use of a 193 presettable counter as a SC/MP address latch. You scampers should get together and write a book before all this knowledge is lost!
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