1)Ethernet Crystal trace length? 2)Hardware Watchdog Timer

[chiranjeevn]

Hi all,

i have two queries...

1) I would like to confirm my understanding on below mention TIP, The  Clock Trace Length should be set up such that the clock signal reaches Ethernet PHY and Processor at the same Time. it means for example the Trace length between Crystal and Processor is 2cm and other end from same crystal to Ethernet should be 2cm is i understood Right? Please assist me?

TIP:

Keep in mind that if RMII is being used the EXTAL0 input must be 50 MHz and the clock trace length

should be setup so that the clock reaches the Ethernet PHY and processor at the same time. Skew

between the two clocks could result in timing violations on the RMII signals.

2)How to implement Hardware Watchdog Timer in K70 processor?Please assist..

[Hui_Ma]

Hi,

1> There without 2cm limitation. When working in RMII mode, indeed a 50MHz external reference must be connected to EXTAL pin, then MII/RMII interface will be able to communicate correctly with the PHY, which will use the same clock. If your PHY presents an output delay compared to input clock, this delay must be properly matched (frequency and phase) to the EXTAL pin, or data corruption will occur. Some PHYs output a 50MHz clock which must be used for MCU EXTAL pin. Others not. Follow your PHY specifications/considerations for RMII mode.

2> About K70 watchdog application, for Kinetis product is using the same watchdog module, I would recommend customer to refer TWR-K20D72M Watchdog demo located at CodeWarrior MCU V10.6 installation default path:

C:\Freescale\CW MCU v10.6\MCU\CodeWarrior_Examples\Processor_Expert\Kinetis\TWR-K20D72M\WatchDog

CodoWarrior MCU V10.6 could be downloaded from here.

Have a great day,
best regards,

Ma Hui

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