SN65HVD257: Two transceivers are setup in redundant configuration

Danilo A.

Part Number: SN65HVD257

Hi Team,

We would like to ask help regarding the customer's inquiry below.

When two Transceivers are setup in redundant configuration, both are enabled no termination on either bus is present. If I transmit data on TXDprime (Pin 1 of U1 and U2 SN65HVD257) and measure signal TXD prime and RXD prime, I can see a train of pulses as attached in the picture (Cannot see data transmitted). No termination are present on CAN bus since I just want to see transmit signal. Is this the expected signal when no termination is present?

When both transceivers are enabled all the time. I connect CAN bus analyser (it has termination) on CAN1 and want to transmit data on CAN1 bus. CAN2 is just enabled and left open (no termination) as I do not want to transmit data on CAN2 bus. But I cannot transmit on CAN1 bus either until I put on termination for CAN2 on board. Are CAN1 and CAN2 not redundant? What is causing this.

Also, when CAN interface is up. It is normal that it will transmit any random data? If I transmit some data it keeps sending it until ACK from other node on that bus right? If other node ACK still it keeps transmitting same data on the bus, it never stops. Is this the expected behaviour?

Thank you for your support.

Regards,

Danilo

over 2 years ago

0 Chris Ayoub over 2 years ago

TI__Genius 15345 points

Hi Danilo,

Are the RXD and TXD pins being pulled high externally from the device? Could you possibly provide a schematic?

These devices are also designed to have termination resistors and they will not work as intended without them. You should definitely include 120 ohm termination resistors on both termination nodes.

After you add the termination resistors can you send the same screenshots.

Best,

Chris

0 Khyati Sapariya over 2 years ago

Prodigy 20 points

Hi Chris,

We have same configuration as in the SN65HVD257 CAN EVM but we are using two TCAN1043HGDQ1 CAN tranceivers.

After adding 120 ohm termination resistor, I could see the transmit data on the scope. Here is the attached signals measured at TXDPrime of TCAN1043HGDQ1 (Blue), RXD of CAN transceiver A (Red), RXD of CAN transceiver B (Green) and RXDPrime of processor (AND of both RXD signals, yellow).
Since there is no other node connected, t could be seen that ACK bit is recessive bit.

https://drive.google.com/file/d/1kMuZQmgsqA4crriO0OOgksyHjCMLoCHL/view?usp=sharing

Thank you,

Khyati

0 Chris Ayoub over 2 years ago in reply to Khyati Sapariya

TI__Genius 15345 points

Hi Khyati,

I am not allowed to open drive files or other file sharing websites on my work computer. Can you post a pdf or an image of the scope shot? You can also email it to me at c-ayoub@ti.com .

Best,

Chris

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SN65HVD257: Two transceivers are setup in redundant configuration