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Charles Blanchard
Associate III
July 21, 2020
Solved

RS485 IT Reception error after initialization

  • July 21, 2020
  • 1 reply
  • 1139 views

Hello,

We are switching from RS232 to RS485 and are encountering problems. Everything worked properly with RS232

After initializing the USART (we are using Cube), transmitting is working fine.

Reception is handled by interrupt. After calling HAL_UART_Receive_IT, callback is instantly called even if nothing is connected to the transceiver and no signal is observed on RX (with the scope). After that, the UART is in error (error callback is also called, sometime its frame error, sometime overruns) and its impossible to receive characters from uart or transmit.

I observed signals with the scope: when transmitting, DE and TX are perfect (before activating the interrupt on rx) and I receive the data on my computer.

When I transmit from the computer, I also see the correct RX.

I don't understand why the rx transfer complete callback is called after enabling the IT...

Do you know from where does it could come from?

Thank you,

Charles

This topic has been closed for replies.
Best answer by Charles Blanchard

Problem solved, it was an hardware problem (floating RX) due to a mysterious tension division bridge..

1 reply

Charles Blanchard
Charles BlanchardAuthorBest answer
Associate III
July 22, 2020

Problem solved, it was an hardware problem (floating RX) due to a mysterious tension division bridge..