RS485 collision detect on stm32f103 of SAE J1708 / J1587

[Olly Kao]

Hi

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I'm trying to implement SAE J1708 / J1587 on stm32f103CB, however I couldn't find how to detect collision occurred, the article ( https://www.kvaser.com/about-can/can-standards/j1708/ ) only mentioned both sending nodes have to release control of the bus, i.e. deactivate their transmitters. But how do I know collision occurs? while the stm transmitting, the SP485EEN enable pin pulls high and receiving terminal got nothing so I can't know how the bus is acting, anyone has an idea??

Thanks