Hello ST Community,
I am working on K-Line communication using an STM32H723ZGT6 controller (EVK board) with a TJA1021T/10/C/118 LIN transceiver. The goal is to communicate with an ECU using ISO-14230 K-line fast initialization.
The hardware path appears to be working correctly. We verified using an oscilloscope that:
1.TXD from STM32H723ZGT6 is switching correctly
2.LIN bus shows dominant pulses during fast-init and UART transmission
3.RXD reflects the LIN signal
4.SLP_N LOW-to-HIGH transition is implemented after power-up
NXP support confirmed that the TJA1021T transceiver operation looks correct based on the waveform captures.
However, the ECU does not respond — only the transmitted request echo is observed.
Important observations:
1.The same STM32H723ZGT6 controller, ECU, and firmware work correctly when using a dedicated K-Line transceiver IC.
2.The UART configuration is 10400 baud, 8N1, and the same firmware and fast-init implementation are used.
3.The fast-init sequence used is 300 ms HIGH, 25 ms LOW, and 25 ms HIGH.
4.The same TJA1021T/10/C/118 IC also works correctly with an ESP32-S3 controller using the same hardware connections.
Because the same firmware and timing sequence work with another K-Line IC and also with the TJA1021 when used with ESP32-S3, we are trying to understand what STM32-specific behavior could affect communication when using the TJA1021.
Could anyone advise on:
1.switching a UART TX pin between GPIO and alternate-function modes on STM32H723ZGT6
2.timing behavior when changing pin modes before UART transmission
Any guidance would be appreciated.
Thank you.
