topic Re: i.MX RT1050 RMII Reference Clock in i.MX RT Crossover MCUs

i.MX RT1050 RMII Reference Clock

pb1 — Mon, 21 Jan 2019 13:27:59 GMT

Hi,

According to the i.MX RT1050 Processor Reference Manual, Rev. 2, the signal ENET_REF_CLK (on pad GPIO_B1_10) is an input in RMII mode. See Table 40-2. ENET External Signals.

Looking at the IMXRT1050-EVKB schematics, however, this signal seems to be an output from the processor, signal name ENET_TX_CLK, which is used to clock the PHY.

Can anybody please explain this apparent difference in documented signal direction.

Thanks for your help,

Pete Baston.

Re: i.MX RT1050 RMII Reference Clock

miduo — Wed, 23 Jan 2019 10:35:17 GMT

Hello,

Well, here I know it is really confused. Please be note that both ENET_REF_CLK and ENET_TX_CLK are inputs to the pins you route them to by default. This had been clearly indicated in the Reference manual.

While, it is yes that for IMXRT1050-EVKB, ENET_TX_CLK is used to clock the PHY. This had been done by software.

By configure ENET PLL(Set ENET1_CLK_SEL to 0 to have the ENET1 TX clock driven by the internal ref_enetpll) and set ENET1_TX_CLK_DIR to 1 to enable ENET1_TX_CLK output driver that will redirect the generated clock to the PHY.

Re: i.MX RT1050 RMII Reference Clock

pb1 — Wed, 23 Jan 2019 11:04:28 GMT

Hi Fang,

Thanks for your reply. So, by configuring these bits in software we have the choice of two modes, with the 50MHz reference clock being either an input or an output ?

Why was the 50MHz clock output mode chosen for the EVKB design ? Is this simply to avoid having a crystal on the PHY ?

Best Regards,

Pete.

Re: i.MX RT1050 RMII Reference Clock

miduo — Thu, 24 Jan 2019 06:58:51 GMT

Hello,

Yes, your understanding is correct.