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I'm using this Ethernet transceiver PHY to study the working of the RGMII interface.

I just want to understand 2 things.

1. What would be the output and input differential voltage levels on the pins 2,3 and 5,6?

If the PHY is to be operated on 100BASE-TX mode, then according to the table values on the electrical characteristics table on page 68, the output voltage (differential) will be only between 0.95V to 1.05V.

  • Am I reading it correctly?
  • In that case, what would be the receive differential voltage levels into the IC? That seems to be not given.

And according to this accepted answers, it is mentioned that 100BASE-T ethernet family has differential peak to peak voltage levels of 2V differential and 1V differential.

  • Then, the above accepted answer would be in conflict with the datasheet values of 1.05V of differential input right? Can someone clarify?

2. Can someone explain the working of figure 18 on page 75?

  • What is the purpose of D1 and D2 along with the RC?
  • How does it work?

P.S.: I checked the wiki page of Fast Ethernet to understand the voltage levels of 10BASE-T, 100BASE-T and 1000BASE-T families of ethernet, but I was not able to find anywhere. If someone could please provide some document or article where I can see the MDI voltage levels of the above ethernet families, it would be helpful for my understanding.

Marcus Müller
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    you say you want to just understand 2 things, then ask 6 or 7 questions, depending on how you count! – Marcus Müller Apr 04 '22 at 11:29
  • @MarcusMüller, yes I agree. I couldn't know how else to ask my questions. I feel my follow-up questions are also related to the main questions. –  Apr 04 '22 at 11:37
  • If you see, some of those, are just confirming my doubts and understandings? Others are follow-up to the main question. I'm doing my homework of trying to understand from other sites and then only arriving here to ask my question. –  Apr 04 '22 at 11:42
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    If you are studying Ethernet, why not read the actual specifications, instead of reading random websites and datasheets of specific chips that implement Ethernet? – Justme Apr 04 '22 at 11:52
  • How to find the actual specifications and where will it be given? –  Apr 04 '22 at 12:07
  • @Newbie you can Google-search for a copy of IEEE 802.3, but it's written in an impenetrable way, but the information is there somewhere. – user253751 Apr 04 '22 at 13:49
  • On the same data sheet (pg. 68) it specifies 1V peak differential output voltage. That is 2Vpk-pk differential. In agreement with the other source. .95 to 1.05 are just ranges. – pat Apr 04 '22 at 21:32

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