topic LPC1769 and PHY DP83848 clock synchronization via CLKOUT pin in LPC Microcontrollers

LPC1769 and PHY DP83848 clock synchronization via CLKOUT pin

jcambiasso90 — Thu, 06 Jun 2019 19:34:58 GMT

Hello, I currently designing a custom board for the LPC1769 with Ethernet connectivity. I know the DP83848 PHY is kinda old but is the only CMSIS-CORE compatible PHY chip I have cheaply and readily available in my country.

The PHY needs an external clock source of 50Mhz to operate in RMII mode so I was wondering if I could use the LPC1769 clock out pin to generate this signal. I found an old schematic for the RBD1768 board using the same PHY chip and they used an external clock generator. I would like to keep the hardware components count as low as possible so again, why not use the CLKOUT pin? Correctly configured in firmware of course.

Also, I would have to connect the CLKOUT pin to the ENET_REF_CLK of the 1769, am I correct? Or is it not necessary?

Thanks.

Re: LPC1769 and PHY DP83848 clock synchronization via CLKOUT pin

Alexis_A — Mon, 17 Jun 2019 21:42:45 GMT

Dear Javier,

I don't see this as a problem but I would recommend you to check previously the frequency. The MCU clock isn't as exact as an external reference clock.

Best Regards,

Alexis Andalon

Re: LPC1769 and PHY DP83848 clock synchronization via CLKOUT pin

jcambiasso90 — Tue, 18 Jun 2019 13:18:01 GMT

Thanks Alexis. Good advice, I have not thought about clock precision. I will come back to this thread once I tested it.