Is Bus Topology possible with Automotive Ethernet?

[jorge_cifuentes]

Hi,

I am planning to use the OM14500/TJA1101JP Automotive Ethernet evaluation board for an academic project. I want to simulate three ECU's in the same bus. Each simulated ECU will be a uC evaluation board connected to a OM14500/TJA1101JP board. Does anyone know if I can plug the three boards in a "bus topology", i.e. all connected on the same wire? If this is possible, which is the recommended way to do it? I am concerned about messing up the expected impedance of the wires by the transceiver.

I want something like this:

Source: https://www.slideshare.net/singhsamit/7-topology-ethernet 

To my understanding, the OM14500/TJA1101JP already has the terminator hardware integrated. Assuming bus topology is possible,  I believe I would not need the terminators at the end of the bus, as indicated in the previous picture. Is my assumption correct?

If bus topology is possible, would connecting the UTP cable pairs together in the way (and using the same connector terminal) shown below would work? 

 

I know NXP has Automotive Ethernet Switches which allows you to plug boards into the same network, but the evaluation boards are pretty expensive. That is why I am looking into cheaper options for setting up my 3-node ECU network. Any guidance will be greatly appreciated.

Thank you!

Best Regards,

Jorge

[Bulat · Accepted solution]

Unfortunately you idea is not realistic. 100BASE-T1 (ethernet interface of the TJA1101) does not support bus topology. Its only allowed topology is point to point. If you need more than two ethernet partners on the net, you have to use a switch like SJA1105.

Regards,

Bulat

[jorge_cifuentes]

Hi Bulat,

I appreciate your explanation. I have two more questions:

1. Would the OM14510/SJA1105TJP evaluation board be ok for creating my network?
2. Which NXP microcontroller eval board(s) with ethernet interface would you recommend me to use to plug to the OM14500/TJA1101JP eval boards? I was thinking about the FRDM-K64F but after taking a look at the datasheet, it does not seem that any of the Jx Connectors have a direct access to the RX, TX and other Ethernet signals from the micro. I need an eval board that provides direct access to the Ethernet pins of the micro.

Please let me know if this question should be posted in a separate post.

Thank you,

Best regards,

Jorge

[Bulat]

1) Yes.

2) OM14500/TJA1101JP is not directly interfaced to our eval boards. Another TJA1101 board has direct connector to a few evaluation boards:

https://www.nxp.com/part/ADTJA1101-RMII#/ 

Regards,

Bulat

[SarRaj]

Hi 

If i wanted to do a point to point connection i can use ADTJA1101-RMII (x2), S32K148EVB-Q176 (x2) right?

I wanted to read some sensor data at one point and need to control some actuators at the other end through spe. 

[jorge_cifuentes]

Thank you very much Bulat for all your help. I finally purchased the following:

- ADTJA1101-RMII (x3)

- S32K148EVB-Q176 (x3)

- OM14510/SJA1105TJP (x1)

I'm glad to be sure that this setup will work :-) I will close the topic now.

Best regards,

Jorge