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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 20th Jan 2022, 6:18 pm   #561
Mark1960
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Default Re: Ortonview PCB

Port D input mode is schmitt trigger with input levels of 0.2Vdd to 0.8Vdd, so would not be compatible with TTL input levels from the MK14. So Karen made these address outputs instead.

If the 887 is TTL level inputs on both B and D then I would agree with Sirius that there is no reason to swap them back, which would maybe allow the same pcb layout for both chips.
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Old 21st Jan 2022, 4:00 pm   #562
SiriusHardware
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Default Re: Ortonview PCB

A couple of (part) tables from the 887 datasheet suggesting that the Port B pins and the Port D pins on the 887 are TTL inputs (when set as inputs) and CMOS outputs (when set as outputs).

Karen had originally intended to use the 887 port D as the bidirectional data bus port but hopefully port B on the 887 is OK for this as well.
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Old 22nd Jan 2022, 5:44 pm   #563
SiriusHardware
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Default Re: Ortonview PCB

Slothie, in #521 you posted a link to your work in progress for conversion to 887 from 877. Is that still active and the latest, or is there an unpublished later version?
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Old Yesterday, 1:26 am   #564
Slothie
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Default Re: Ortonview PCB

Quote:
Originally Posted by SiriusHardware View Post
Slothie, in #521 you posted a link to your work in progress for conversion to 887 from 877. Is that still active and the latest, or is there an unpublished later version?
I think thats the latest, its certainly the one that works "best". I think I tried something else but that made it less stable, so I reverted it.
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Old Yesterday, 9:29 am   #565
Slothie
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Default Re: Ortonview PCB

I forgot to mention that The latest version of this branch (PIC16F887) is available publicly at https://bitbucket.org/IanKRolfe/orto...src/PIC16F887/
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Old Yesterday, 10:12 am   #566
SiriusHardware
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Default Re: Ortonview PCB

Just to recap, I think you said that it generates a stable video image but doesn't appear to be reading the data, at least from an MK14 or replica. If so I'd be interested to see if it can render an image from an EPROM like Karen's prototype, or whether it works when you do your trick of connecting the data lines to the lower address lines.
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Old Yesterday, 10:24 am   #567
Slothie
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Originally Posted by SiriusHardware View Post
Just to recap, I think you said that it generates a stable video image but doesn't appear to be reading the data, at least from an MK14 or replica. If so I'd be interested to see if it can render an image from an EPROM like Karen's prototype, or whether it works when you do your trick of connecting the data lines to the lower address lines.
Because it was crashing the MK14, I was running it unconnected and configured to read from the RAM. The ram chip I was using defaulted to alternate bytes being 0x00 and 0xFF but I was just seeing all zeroes ('@' in text, blank in graphics). I didn't try connecting the data and address lines.

I'm going to dig it out and give it another look at, I came across my USB logic analyser the other day and that helped a lot with seeing the timing problems that Mark ultimately found a fix for. It had been put somewhere "safe"!
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Old Yesterday, 10:31 am   #568
SiriusHardware
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Default Re: Ortonview PCB

One stunt you could try is to put a programmed E(E)PROM (2716? 2816?) in place of the 6116 to give the OV known fixed memory content that it should be rendering from rather than the expected pseudo-random content of the RAM. That would save mucking about with wiring data lines to address lines etc.
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