topic Re: When TXEN_N set high, RX packets are not received by CAN with TJA145B Transceiver in In Vehicle Networking

When TXEN_N set high, RX packets are not received by CAN with TJA145B Transceiver

william_dodgy — Fri, 05 Sep 2025 03:00:23 GMT

FYI: TXEN_N is controlled by PMIC in our system.

After the initialisation of TJA1465B to Normal mode along with other settings as per datasheet and pulling TXEN_N pin low by PMIC, I am able to receive and transmit CAN packets. As per data sheet, Setting TXEN_N pin HIGH, transceiver transmitter is disabled and have the receive capability. However, after setting HIGH by PMIC, I am unable to receive packets from ECU(PCAN in our case as external CAN node).

The transceiver mode still in NORMAL mode after setting TXEN_N pin HIGH and I also see signal on RXD pin translated from CANL and CANH by transceiver TJA1465B.

Re: When TXEN_N set high, RX packets are not received by CAN with TJA145B Transceiver

guoweisun — Fri, 05 Sep 2025 07:14:47 GMT

Can you give some waveforms including the TXEN_N/ RXD controlled by PMIC or external power signals?

Re: When TXEN_N set high, RX packets are not received by CAN with TJA145B Transceiver

william_dodgy — Fri, 05 Sep 2025 12:48:16 GMT

One quick question, if the transmitter is disabled on the TJA1465B transceiver side, how does the transmitter node gets ack bit from receiver node ?

Re: When TXEN_N set high, RX packets are not received by CAN with TJA145B Transceiver

william_dodgy — Fri, 05 Sep 2025 16:54:22 GMT

Here is the detailed analysis: FYI: Baud-rate chosen is 500KBPS for arbitration phase and 2MBPS for Data phase. classical CAN message is used for analysis.

1. CAN Bus has two nodes.

In Normal case where setting TXEN_N low and putting transceiver into Normal State, Transmit Node (PCAN) sends the CAN frame along with recessive ACK bit and monitors the same bit to check that the packet is received by the Node connected to the bus. Once the receiver node receives and then sends the dominant ack bit in the ack slot. This observation can be seen on the below capture. (FYI: Able to receive both Classical CAN, FD-CAN with both extended and standard IDs.

In case of TXEN_N pin setting HIGH, TJA1465B transmitter is disabled. when I send the packet from PCAN transmitter node, receiver node didn't receive the packet, and no Ack bit is sent by the receiver node instead it is sending an active error flag of 6 bits on TX pin of the receiver Node. Because MCAN protocol errors getting generated. the captured picture is pasted below:

2. When CAN bus has three nodes.

In case of TXEN_N pin setting HIGH, TJA1465B transmitter is disabled. when I send the packet from PCAN transmitter node, both the receiver nodes receive the packet, and Ack bit is also sent by the receiver's node.

Re: When TXEN_N set high, RX packets are not received by CAN with TJA145B Transceiver

guoweisun — Tue, 23 Sep 2025 05:57:43 GMT

You didn't show me the waveform TXEN_N/ RXD controlled by PMIC or external power signals.

I just want to know the distinguish between these different control.