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What will happen if I desolder the 25 MHz clock of an ethernet module (like this one; datasheet of the chip) and add a faster clock (say 100 MHz)? The related product is a 10BASE-T ethernet module. But is the 10 Mbps limit related to the chip or the clock?* In case the limit is not related to the chip, will I get a higher speed, data corruption, ...?

According to Wikipedia 100BASE-TX ethernet uses a 25 MHz clock and 10BASE-T a 2.5 MHz clock so I am actually confused why they use the faster clock for their low speed ethernet controller.

I know that the speed is also related to the encoding. But for my application I actually need the Manchester encoding of 10BASE-T, yet with a higher speed.

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    (note: this was how 100mbps was first done. over 10base-2 even.) As long as that clock isn't referenced for bus transfers, and the chip can actually run that fast, it'll work. (as expected, only to another module hacked in the same way. it'll never talk to 802.3 compliant devices.)
    – Ricky
    Oct 26, 2015 at 21:38
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide your own answer and accept it.
    – Ron Maupin ♦
    Aug 7, 2017 at 0:28

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If you aren't at all concerned with interoperability with other devices, you could try to do what you want, but increasing the clock also means that the other end needs to be identically configured, and the cabling in between, which is rated, depending on category, for certain signal speeds, would need to be compatible (e.g. crosstalk), too. Also, any firmware and software for driving the module would need to be checked for compatibility.

It is doubtful that changing the clock will actually work for anything. It could be an interesting experiment, but you would need to do it on two devices to test it.

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  • Thanks for your answer, Ron. Actually I intend to use two of these modules configured in the same way. Cable lenght should be well below 1 m; more like some centimeters. Firmware/software is easier to alter than the hardware. Also, these are potential problems if it would work at all. Still, the main question is: chip limit or clock limit? If it is a chip limit my approach would not work at all and either I have to live with the low speed or think of something else.
    – urgos
    Oct 25, 2015 at 21:55
  • The clock drives the chip, which may burn out at a fast clock rate, but there is no way to tell. It may work just fine, or, like CPUs driven to an extreme clock rate, it may fail. The clock rates discussed are certainly much lower than those used for CPUs, but that is no guarantee.
    – Ron Maupin ♦
    Oct 25, 2015 at 21:59

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