Project: HDMI/DVI out for STFM

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Icky
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Re: Project: HDMI/DVI out for STFM

Post by Icky » Thu Dec 06, 2018 12:00 am

Would be interesting to see how troed’s behaves at different voltages. See if he can replicate the same behaviour I am experiencing.

Still at 4.3V and on 5th loop now in GEMBench and no resets.

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Re: Project: HDMI/DVI out for STFM

Post by exxos » Thu Dec 06, 2018 12:19 am

Can you measure the voltage from the PSU 0v to 0v on the HDMI connector ( or somewhere as far up the board as possible) ?
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Icky
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Re: Project: HDMI/DVI out for STFM

Post by Icky » Thu Dec 06, 2018 7:41 am

exxos wrote:
Thu Dec 06, 2018 12:19 am
Can you measure the voltage from the PSU 0v to 0v on the HDMI connector ( or somewhere as far up the board as possible) ?
I did not get to this last night. CPU failed on my PC. Am not doing well with several PSU issues last month and now CPU failure this month.

I should get time to look at this tonight.

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Smonson
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Re: Project: HDMI/DVI out for STFM

Post by Smonson » Thu Dec 06, 2018 9:14 am

Sorry to hear about your CPU Icky. That really sucks.

Also I ran my machine on an ATX PSU at 5.06v for over fifteen minutes, but unfortunately didn't experience a single bad read. Ah, well.

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Re: Project: HDMI/DVI out for STFM

Post by tuxie » Thu Dec 06, 2018 9:49 am

Did someone check the ground ? Check how stable the ground against the ground on the PSU directly is ? We found very often a lot of mistakes with the ground. For example when the ground is not stable enough then the logic pulls the ground high and when the level of the ground signal goes over a specific value then the logic cant recognize a Zero Value anymore.

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Re: Project: HDMI/DVI out for STFM

Post by Smonson » Thu Dec 06, 2018 10:00 am

I measured a differential of around -4 millivolts between the FPGA board to the chassis ground (measured off the big electrolytic near the power supply). Not too bad considering the whole mod draws a lot of current (over 300mA).

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Re: Project: HDMI/DVI out for STFM

Post by czietz » Thu Dec 06, 2018 10:43 am

I think tuxie's comment was more meant to measure the dynamic ground offset (not the DC offset). I.e. he was saying the same as me in viewtopic.php?f=29&t=330&start=360#p15179.

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Re: Project: HDMI/DVI out for STFM

Post by exxos » Thu Dec 06, 2018 10:53 am

Smonson wrote:
Thu Dec 06, 2018 10:00 am
I measured a differential of around -4 millivolts between the FPGA board to the chassis ground (measured off the big electrolytic near the power supply). Not too bad considering the whole mod draws a lot of current (over 300mA).
That doesn't sound right.. With a scope across grounds you should see ringing and all sorts of chaos likely going +/- 1V or so.

This is a example of VCC rail.. (images taken a couple years ago)

n2.png
n2.png (2.08 KiB) Viewed 764 times

and a gnd spike..

n1.png
n1.png (1.53 KiB) Viewed 764 times

This was across the CPU pretty much, so like 1cm of track. Once it gets to like a foot long trace, welcome to crazy town!

I don't know how immune FPGA are, put some inputs can "latch up" if the voltage is to high or low on a input.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Re: Project: HDMI/DVI out for STFM

Post by Smonson » Thu Dec 06, 2018 11:19 am

Oh, right. That was a DC offset. On the scope I saw occasional noise on the HDMI board ground of up to about +/- 650mV relative to PSU ground. But that shouldn't affect the level shifting buffer direction signal, I think, as it's localised to the mod board only.

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Re: Project: HDMI/DVI out for STFM

Post by exxos » Thu Dec 06, 2018 11:42 am

Smonson wrote:
Thu Dec 06, 2018 11:19 am
Oh, right. That was a DC offset. On the scope I saw occasional noise on the HDMI board ground of up to about +/- 650mV relative to PSU ground. But that shouldn't affect the level shifting buffer direction signal, I think, as it's localised to the mod board only.
As a mad idea, could you double the length of your ribbon cable on your board and try tests again ? Make sure PSU is at 5V or even 5.2V.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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