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AM4378: Rise time/ Fall time query

Sri Viswa Sathiamoorthy
Intellectual 290 points

Part Number: AM4378

Hi,

In the datasheet of AM4378 processor pgno: 139, the required rise/fall time is provided as 1ns to 5ns. 

1)Whether we can use this requirement for TXD[0:3], RXD[0:3]?

2)What happens when rise/fall time is less than 1ns?

Thanks

VIswa

  • 0
    TI__Mastermind 27890 points

    Hello,

    A1: Yes for RXD, no for TXD. We do not specify output rise times as they are heavily influenced by the customer's implementation.

    A2: These values are from the industry standard interface specification so I would not (can not) recommend deviating from it. Practically? It's unlikely to cause a problem unless there is a significant deviation. From a technical perspective you may see increased system noise and/or additional energy coupling into adjacent signals via crosstalk but adhering to best-practices in your layout (see SPRAAR7) should help to minimize this. You'd also need to account for this in your interface timing analysis. Note that I can only speak for the MAC (SoC) side. There are many partner PHYs available in the market and they may/may-not have an issue if your Rt/Ft deviates from the specification.