STE video chip

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Badwolf
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Re: STE video chip

Post by Badwolf »

Steve wrote: Tue Jan 11, 2022 12:47 pm The 32mhz looks terrible doesn't it?
Definitely not pretty.

How does the 16MHz line look versus the 32 (as per Exxos' images above)?

BW
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Re: STE video chip

Post by Steve »

@Badwolf

I got a better picture here, my yellow channel probe seems to be a bit dodgy and the last images were just wrong... I played with it a bit and got a clean signal but the voltage levels don't seem right.

That's 32 and 16:

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Re: STE video chip

Post by exxos »

Steve wrote: Tue Jan 11, 2022 5:55 pm I played with it a bit and got a clean signal but the voltage levels don't seem right.
Assuming both your probes are on X10, then press the CH1 button and make sure the PROBE menu is on X10 (Also check for CH2)
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Re: STE video chip

Post by Steve »

Ahh ok thx I'll check that out next time :)
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Re: STE video chip

Post by exxos »

I have drafted out a possible fix.

The problem is the datasheets never commit to exactly how long the delay is. " somewhere between 1ns - 5ns" is as good as it gets. Though this does not actually help when we need a 5ns delay :roll:

So the idea is that the first buffer (IC4) will be the minimum delay time. Possibly 1ns, possibly 5ns. the first solder jumper allows to isolate ( un-load) the second buffer.

The variable resistor section can be switched in or out the series link both buffers. Possibly 2ns, possibly 10ns.

The variable resistor adds a simple delay line which is variable from about 0ns to 10ns.

Overall the delay line can be variable from 1ns to about 20ns. There is just no way to know what the delays are without physically building it. From memory the buffers were incredibly quick like 1ns. so two of them in series is 2ns, plus the variable delay, assuming the preset is set midway, it should overall add about 7ns by default. This should be enough to delay the 16Mhz line so it is in proper sync to the 32Mhz clock.

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Re: STE video chip

Post by Badwolf »

Steve wrote: Tue Jan 11, 2022 5:55 pm I got a better picture here, my yellow channel probe seems to be a bit dodgy and the last images were just wrong... I played with it a bit and got a clean signal but the voltage levels don't seem right.
Holy about-10ns-near-perfect-out-of-phase transitions, Batman!

Thanks, Steve.

@exxos does this smell deliberate to you? the peaks and troughs are almost perfectly in phase rather than the edges. Such a stark difference from the older chip makes me wonder if it were introduced to match the requirements of a newer MCU or something?

Dunno. I could be seeing ghosts but seems awfully shonky if it's by accident.

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Re: STE video chip

Post by exxos »

Badwolf wrote: Wed Jan 12, 2022 10:06 am @exxos does this smell deliberate to you? the peaks and troughs are almost perfectly in phase rather than the edges. Such a stark difference from the older chip makes me wonder if it were introduced to match the requirements of a newer MCU or something?

Dunno. I could be seeing ghosts but seems awfully shonky if it's by accident.
Doubt it. I've seen this odd type of skew before. I've even talked about it in the past. If you think about it, a perfect sync on falling edges is almost impossible, you will always have delays. But the clocks ARE in sync. So Atari must have added internal buffers to equal the delays. So they changed manufacture of chips, those delays no longer add up. Considering the skew seems to be a few ns to short, it fits the "newer chips are faster" type of thing, so timings get shifted and things screw up.
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Re: STE video chip

Post by exxos »

First PCB draft done.

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EDIT:


:WTF: 5V looks connected, but Eagle says its not ?!

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Re: STE video chip

Post by Badwolf »

exxos wrote: Tue Jan 18, 2022 11:50 am :WTF: 5V looks connected, but Eagle says its not ?!
I occasionally see something like that in Kicad 5. Solution is normally to lift the component. Recalculate the flood, place the component again.

Dunno if that'll help with Eagle?

BW

PS: I had a quick look yesterday and my STE has the suspect -1712. I'll have to try to scope my lines at some point too.

Not noticed any graphical issues, mind.
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Re: STE video chip

Post by exxos »

Badwolf wrote: Tue Jan 18, 2022 12:51 pm PS: I had a quick look yesterday and my STE has the suspect -1712. I'll have to try to scope my lines at some point too.

Not noticed any graphical issues, mind.

Just put your scope probe on the 16Mhz line.. If it is borderline then it will mess up..
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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