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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 Aug 2021, 7:06 pm   #181
SiriusHardware
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Default Re: Ortonview PCB

Powering the populated board from just 5V, things look a bit more normal. Next step will be to try it in V1 Ortonview configuration, with buffers linked out and four capacitors fitted. I'm expecting the through-hole 220pFs to arrive tomorrow, so I will continue then.
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Old 4th Aug 2021, 7:13 pm   #182
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Default Re: Ortonview PCB

Hmm seems the buffer idea needs a lot more work then.
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Old 4th Aug 2021, 7:27 pm   #183
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Unfortunately it affects the MK14 so badly when connected that I would be reluctant to try to faultfind that way. As said, I'll make sure it still works in the original way with capacitor fix just so I know that nothing is broken.

The 'normal' MK14 switch on prompt is there at switch on just with a lot of noise on the displays, but it crashes within a second or so. It might just be that the buffer enable delay time needs to be a little bit longer.
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Old 4th Aug 2021, 7:42 pm   #184
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Default Re: Ortonview PCB

I've just tried manually 'slugging' another capacitor across the existing 220pF - the MK14 keeps running, albeit still with a lot of noise on the displays, and I can step through addresses with the 'Mem' key. However the addresses sometimes increase in large steps by themselves each time I press 'Mem'. I think there's still a chance that the right delay could fix it, but it might have to be more precisely timed, ie, by the PIC rather than by external timing.
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Old 4th Aug 2021, 7:42 pm   #185
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Well its an improvement over having no delay at all, the display was badly corrupted and sometimes there was nothing on the display at all. The PIC doesn't attempt to use the bus for some time after asserting NENIN so their certainly is scope to increase the capacitance (delay) considerably.
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Old 4th Aug 2021, 7:47 pm   #186
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How much time is 'some time', do you remember?
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Old 4th Aug 2021, 7:55 pm   #187
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Default Re: Ortonview PCB

What value resistor did you use for the RC delay to the Buffers?

With two 74ls ttl inputs on the output of the RC delay, the maximum resistor value is probably 1 k to make sure it can pull the inputs down to less than 0.8 v. A lower value, say 470 ohm might be a better choice, but then the capacitor needs to be a higher value.

I was never much good at calculating RC timing values, I think you want to aim for about 1.5 to 2 us. Based on 8060 memory cycle time at 4MHz.

Last edited by Mark1960; 4th Aug 2021 at 7:57 pm. Reason: Added reason for estimated delay required.
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Old 4th Aug 2021, 7:58 pm   #188
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Quote:
Originally Posted by SiriusHardware View Post
How much time is 'some time', do you remember?
It was 3.75uS according to my calculations (15 machine cycles). I think 1K & 220pF should give a delay of about 220nS so 1nF should give you 1mS?
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Old 4th Aug 2021, 8:00 pm   #189
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Originally Posted by Mark1960 View Post
What value resistor did you use for the RC delay to the Buffers?

With two 74ls ttl inputs on the output of the RC delay, the maximum resistor value is probably 1 k to make sure it can pull the inputs down to less than 0.8 v. A lower value, say 470 ohm might be a better choice, but then the capacitor needs to be a higher value.

I was never much good at calculating RC timing values, I think you want to aim for about 1.5 to 2 us. Based on 8060 memory cycle time at 4MHz.
I suggested a 1k resistor, so C should be 1.5-2nF, looks like I suggested a value far too small.
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Old 4th Aug 2021, 8:12 pm   #190
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Default Re: Ortonview PCB

Slothie suggested 1K + 220pF so that's what it is at the moment. I stuck an additional capacitor marked '470' across the 220- it's an old British capacitor so the chances are that the value really is 470pF and not 47pF (a more modern 470pF capacitor would be marked '471').

I'm wondering if it would be more productive to knock up a proper monostable delay using a 74121 / 74122 with a multiturn pot to allow free adjustment of the delay in very small increments and generate the delay with that. If that gives us a working delay range we can try to fall back to RC generating the same delay.
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Old 4th Aug 2021, 8:24 pm   #191
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Default Re: Ortonview PCB

Quote:
1K & 220pF should give a delay of about 220nS so 1nF should give you 1mS?
Surely you mean 1uS? (1000nS in a uS?)

Am I looking at more like 2.2nF then, based on Mark's suggestion of 2uS?
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Old 4th Aug 2021, 8:43 pm   #192
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Default Re: Ortonview PCB

Well, just tried a '222' (2,200pf / 2.2nF) and the situation is much the same, unstable and crashing.

I really will need to try it in the original mode just to make sure the PIC and memory are still OK. The 365 buffers were brand new from RS or Farnell a while ago and were actually tested in my SOC VDU as 80L95 substitutes.

I'll have to pause until the 220pF through hole caps arrive, hopefully tomorrow.
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Old 4th Aug 2021, 8:48 pm   #193
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Default Re: Ortonview PCB

Quote:
Originally Posted by Slothie View Post
Quote:
Originally Posted by SiriusHardware View Post
How much time is 'some time', do you remember?
It was 3.75uS according to my calculations (15 machine cycles). I think 1K & 220pF should give a delay of about 220nS so 1nF should give you 1mS?
So I think we need to aim for a delay between 2us and 3.75us, an RC on ls ttl inputs might not be that accurate without selecting the values on test.

Maybe safer to use too large a value instead of too small to avoid bus conflict, so perhaps a 3.3nF and see what that gives, then trim with the resistor.
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Old 4th Aug 2021, 8:52 pm   #194
SiriusHardware
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Default Re: Ortonview PCB

Noted, although 2.2nf seems no better than 220pF+470pF - as said, I think I should first verify that it operates normally in the original way with your capacitor fix on A8-A11 before trying to get something new working.
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Old 4th Aug 2021, 8:54 pm   #195
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Default Re: Ortonview PCB

You could try isolating U3-6 from R12 and NRDS using a schottky diode and then connect the second gate pins of the buffers to U3-6 instead of using an RC.

Last edited by Mark1960; 4th Aug 2021 at 8:55 pm. Reason: typo again
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Old 4th Aug 2021, 8:59 pm   #196
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Default Re: Ortonview PCB

Noted as well, but I'm still going to go back to basics first to ensure that I still have a fully working PIC, etc. I need to start from a known good datum point, I think.

Just think, Mark, you have all this fun to look forward to, although hopefully we will have it all worked out by the time your board gets to you.
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Old 4th Aug 2021, 9:03 pm   #197
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Default Re: Ortonview PCB

Quote:
Originally Posted by SiriusHardware View Post
Quote:
1K & 220pF should give a delay of about 220nS so 1nF should give you 1mS?
Surely you mean 1uS? (1000nS in a uS?)

Am I looking at more like 2.2nF then, based on Mark's suggestion of 2uS?
Yes I meant uS not mS. Tired typing!
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Old 4th Aug 2021, 9:16 pm   #198
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Default Re: Ortonview PCB

Well I confirmed my two PIC16F877 sourced from utsource last year can be erased and programmed with my GQ4x4 programmer, which was also first time I’ve used that too. My phono connectors look like they are the right type. DIP switches are piano type, but should fit ok. Not sure about 16MHz crystal, I might have one, but I do have a few 48MHz third overtone that seem to prefer 16 MHz without fine tuning the notch filter.

Still need to solder a connector to the MK14, probably same as Slothie, female header on the MK14 and male on the Ortonview.
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Old 4th Aug 2021, 9:27 pm   #199
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Default Re: Ortonview PCB

Another possible method without cutting any more tracks would be to connect UA11 to the second gate input on the buffers, with a pullup resistor, but then only the 6116 ram can be used for ortonview, but we still need to make sure we are not corrupting the MK14 ram.
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Old 4th Aug 2021, 9:37 pm   #200
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Default Re: Ortonview PCB

Mine has a conventional 32 + 32 edge connector soldered to the 'fingers', so that I could (If I chose) connect it to my original MK14 for compatibility testing purposes, although I would need to remove the RAM since my issue II doesn't have the memory hole for it to occupy.

Original MK14s don't have Clock-Out on the rear edge connector but, luckily, OrtonView does not need it. Of course I would also need to route the buses and control signals to the underside of the edge connector where the issue II doesn't even have fingers to solder the signals to. So on the whole, highly unlikely.

Have to say the Slothie PCB based version looks a whole lot neater than the danglesome veroboard memory expansion 'bridge' board and the absolute rat's-nest of an OrtonView prototype I had hanging off that, so even if it only ever works in its original way with the A8-A11 capacitor bodge, I'll be very happy with it.

If you didn't want the VDU feature you could probably saw the rear two thirds off the PCB and the memory expansion would still work like a traditional plug in Sinclair 1.5K 'RAM Pack' for the issue VI PCB.

Last edited by SiriusHardware; 4th Aug 2021 at 9:52 pm.
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