SJA1105 RMII ref_clk configuration

[georgwaibel]

Hi,

I have a board where a PHY is connected to a SJA1105Q switch via RMII. Other than descripbed in the switch reference manual, the 50MHz reference clock is generated by the PHY and supplied to the switch port's REF_CLK pin.

Is it possible to configure the REF_CLK pin to be an input when the switch port is in MAC mode?

Regards

Georg

[Bulat]

No, it is not possible. In MAC mode RMII port of the switch outputs REF_CLK only. You can either, change configuration of the PHY to use external REF_CLK (from the switch), or set the switch's port to RMII PHY mode.

Regards,

Bulat

[Yangg]

Hi,NXP experts，

There is a description in datasheet page15 like below.From my understanding the REF_CLK can be used as an output even acts as RMII MAC  mode.

Can you please explain more?Thank you.

"RMII data is exchanged via 2-bit data signals TXD[1:0] and RXD[1:0] as shown in
Figure 7. Transmit and receive signals are synchronized with the shared reference clock,
REF_CLK.
In both the PHY-MAC (i.e. PHY to switch) and MAC-MAC (i.e. processor to switch)
configurations, the REF_CLK output on the Ethernet switch can provide the shared
reference clock."

BR

Yang