Questions regarding Level Shifting on FXPAK Pro and Super Everdrive

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Ziggy587
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Joined: Fri Oct 08, 2010 6:08 pm
Location: NY, USA

Questions regarding Level Shifting on FXPAK Pro and Super Everdrive

Post by Ziggy587 »

Hey everyone, I had some questions regarding the level shifting found in the Sd2snes/FXPAK Pro and the Super Everdrive.

Looking at some pics online, I can see that the Sd2snes used the 74ALVC164245 for 5v to 3.3v level shifting. It looks like some variations of the Super Everdrive have used this one as well. And looking at some pics of newer revision FXPAK Pros, it looks to be using a 74LVT162245.

SN74ALVC164245 Datasheet

SN74LVT162245ADGGR Datasheet

My question is regarding the resistors that the signals pass through before hitting the level shifters on the Sd2snes/FXPAK Pro. Are they being used for current limiting? And if so, are they really necessary? Or is there some other reason (perhaps specific to this FPGA)? Because looking at pics of the Super Everdrive, the signals are fed straight from the cart edge to the lefter shifters. That's not to say that just because you found an example of something proves it to be correct, which is why I'm asking.

Also, why are the data signals being passed through ferrite beads? I've downloaded the Sd2snes project from Github, but I'm getting various errors when trying to load it in KiCAD. But from what I can see, the 8 data lines are being passed through ferrite beads before hitting the transceiver. Is this really necessary?

Some pics for reference (you can right-click>view image in new tab to see the full resolution)...

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lidnariq
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Re: Questions regarding Level Shifting on FXPAK Pro and Super Everdrive

Post by lidnariq »

I'm guessing they're there to help reduce reflections. Reflections have been a dramatic problem in the NES, so it's credible it'd come up in the SNES too.
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Ziggy587
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Re: Questions regarding Level Shifting on FXPAK Pro and Super Everdrive

Post by Ziggy587 »

Thanks. I was reading a bit about signal reflections, but a lot of articles seem to talk about them in regards to cables. But I'm assuming the phenomenon is more or less the same between cables and signal traces?

I also PM'ed ikari_01 this question (I saw that he hadn't visited this forum in a few years) but I forgot to link this thread to him. If he ever replies, I will update his answer here.
creaothceann
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Re: Questions regarding Level Shifting on FXPAK Pro and Super Everdrive

Post by creaothceann »

A trace is also a cable, just a bit less flexible.
My current setup:
Super Famicom ("2/1/3" SNS-CPU-GPM-02) → SCART → OSSC → StarTech USB3HDCAP → AmaRecTV 3.10
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