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FRDM-K64F freedom develpment board as a guideline for a new PCB. With this design a 50MHz clock is generated by the RMII Ethernet PHY and routed to the EXTAL0 (pin 50) of the K64 cpu. Of interest, the FRDM-K64F Rev E3 schematics show the XTAL0 output (pi

Question asked by David OLSEN on Dec 15, 2015
Latest reply on Dec 17, 2015 by Kerry Zhou

We are using the design for the FRDM-K64F freedom development board as a guideline for a new PCB. With this design a 50MHz clock is generated by the RMII Ethernet PHY and routed to the EXTAL0 (pin 50) of the K64 cpu. Of interest, the FRDM-K64F Rev E3 schematics show the XTAL0 output (pin 51) connected to GND thru a 0-ohm resistor (R74) via XTAL_K64_MAIN. When using an external clock, normally you leave the XTAL output unconnected. Why is this output connected to ground?


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