RMII with external oscillator

[Thomas_Socomec]

Posted on February 29, 2012 at 10:10

Hello,

I have a problem to communicate with a PHY when I use an external oscillator for the Ethernet part. If I use the clock generated by the microcontroller (MCO pin) there is no problem, the communication work fine. But if I connect the external oscillator instead of the MCO pin, the communication (through the pin MDIO and MDC) does not work. In my source code I have just removed the configuration of the MCO pin. I think in this case the microcontroller can not recognize the external oscillator and a problem of clock occurs. If somebody has already used an external clock for the Ethernet part, I am interesting to know how to configure the registers in this case. Thank you in advance ! Thomas #ethernet #phy #clock #rmii

[amin23]

Posted on February 29, 2012 at 18:06

Hi,

I did a test it works fine, you should do as below: - remove JP5 - enable RMII mode: Uncomment the define #define RMII_MODE and comment the define #define MII_MODE - the attached file explains how to connect external oscillator (ref SM7745HEV-0M or equivalent) on the U3 footprint ________________ Attachments : Ext_Oscil.PNG : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006I0xQ&d=%2Fa%2F0X0000000bh6%2F6DtiYZaCWfL5K_BiGu.xKpH1_RBD_sBgji2_jbfrrDM&asPdf=false