On all my previous XMOS ethernet designs I've always used a 25MHz oscillator and sent it to both the XMOS device for it's clock and my ethernet PHY (sometimes with a schmitt trigger in between). However, I notice that several of the reference XMOS designs use separate oscillators/crystals for the device clock and the ethernet PHY.
Is there a reason for this that I'm missing?
Sharing XMOS device and ethernet PHY clock? Topic is solved
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Redeye
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henkVerified
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Maybe because another clock may be needed for USB or Audio?
There is no reason not to run an XCore of a 25 MHz clock if you just use Ethernet.
There is no reason not to run an XCore of a 25 MHz clock if you just use Ethernet.
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Redeye
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In some circumstances, yes that would explain it, but not always. For example, on the xCore-200 eXplorer board it uses a 24MHz clock for the XMOS device and a separate 25MHz clock for the ethernet PHY. Why not just use a single 25MHz clock for both?
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henkVerified
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Hi Redeye,
That is because of the USB PHY.
The xCORE200 can run on either 24 or 25 - but it can only use the USB PHY when running of a 24 MHz oscillator (or maybe a multiple).
Cheers,
Henk
That is because of the USB PHY.
The xCORE200 can run on either 24 or 25 - but it can only use the USB PHY when running of a 24 MHz oscillator (or maybe a multiple).
Cheers,
Henk
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Redeye
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Ah, right. Now it makes sense. I knew there'd be an obvious explanation that I was completely missing. That'll be because although I'm using an XE232, I won't be using the USB sections at all, so I can use a single 25MHz clock as I have done before.
Great. Thanks for your help.
Great. Thanks for your help.