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STM 5″ – RS485 Fix

Explanation how to fix problem with not working RS485 on STM 5″ boards PCB 50STM32U5 with revison 1.0 and 1.1.

If you are able to do this by yourself then folowing the steps below should help you solve the problem. If you are not sure or you think you could “mess up” something please contact us for further inforamation.

To start with you need to cut the “roads” as shown on the below picture.

Expansion conn cannot complete the full HW 485. This means that the DE signal can be manually used as any GPIO out and e.g. USART1 TX and RX.

Also modify project code as below:

USART6 RX, TX and DE pins are not properly routed to RS485 transceiver.

As a workaround PE4 should be connected to pins 2 and 3 and PJ4 needs to go to pin 4 of RS485 transceiver.

To achieve that, tracks on PCB needs to be modified as on picture below.