MPC5777C-516DS FEC with RMII and DSPI_E

[DKa]

Hello,

we want to use all 5 SPI modules of the MPC5777C combined with the FEC in RMII mode. The problem is, that the FEC_RXER signal has the same pin as the DSPI_E_SOUTE signal. So far i couldn't find a way to use both.

We want to use the Ti DP83822HRHBR as PHY. The Datasheet of the DP83822HRHBR mentions on Page 30 that the RXER signal is optional in RMII mode, also in the description of the MII-Lite mode on Page 2408 of the MPC5777C Reference Manual there is a description, which mentions that the MII-Lite can be used without FEC_RXER, which is possible by a corruption of the CRC by the PHY.

1.) Is it possible to use the FEC in RMII mode without the FEC_RXER signal in combination with the DP83822HRHBR?

2.) If we use the DSPI_E_SOUT while using the FEC in RMII mode without the FEC_RXER, is there a possibility that the DSPI_E_SOUT signal disturbs the FEC via the FEC_RXER?

[PetrS]

Hi,

As far as I know the RM does not indicate RX_ER can be omitted in the RMII mode. This can be done in MII-lite mode and user should tie RX_ER low in this case.
So your intended connection will not be possible, I think.
Option could be use more slaves/chip selects on other SPI modules.

BR, Petr

[San_96]

Hi NXP Team,

I need a clarification here. In MII-Lite mode, RX_ER shall have pull down. Is this what you mean by the statements above?

1. As per my understanding, FEC_TXD2/FEC_RXER are multiplexed on same pin. And that pin is used as FEC_TXD2. So, RX_ER (as per your reply) is the pin of PHY module. Is this correct ?

2. If this is pin of PHY module, can I leave the RX_ER unconnected (no PD/ no PU) in MII-Lite mode?

Thank you in advance.