Half duplex RS485 communication using Colibri T30

I am trying to use RS485 interface with Colibri Eval Board and Colibri T30 having embedded Linux OS. It has kernel version 3.1.10-V2. The setup includes jumper settings: JP11 close (Echo off), JP12,JP14: open, JP13,JP15: close (Half duplex comm), JP16: close (upper RS232 disable). I am using RXD+ and RXD- lines for communication which are connected to X2 bottom DB9 connector. I have connected a RFID reader which sends a string of data on 485 lines when presented with a RFID tag. I have verified this using USB to RS485 converter and serial terminal utility on windows pc. I am unable to do the same using mention SBC setup using minicom. The port is set to ttyHS3 in minicom as 485 interface is connected to UART-B of the Colibri Module. Please guide me to get the interface working.

hi Rahul

There is no Transceiver Control Support in Tegra Modules. We never tested RS485 half duplex mode on T30. We will need time to test this.

So we have some questions:

What is your use case? What is the communication speed? How many devices are on the RS485 network? Can you share a timing diagram for the communication?

hello Jaski,
I will be needing RS485 interface to connect 20 RFID readers which will be sending RFID tag data one after another at baudrate of 9600. Current I have only one reader which I need to listen to for RFID tag id he will send.

Thanks for the information.

May I ask what is other use case of the module? I am asking this, since if you don’t need any high performance GPU, you should also go for colibri-imx6 which provide the RS485 support.

Thanks for the reply.
I am going to use ethernet, RS232 (2) and RTC in my project. I am later on going to use iMX7 SoM but I wanted to try the RFID interfacing with currently available T30.

Problem solved !
RTS signal controls the direction of data in half duplex rs485 communication on colibri eval board. pyserial provides support for this thus resolving my issue. The port was in transmit mode hence was not able to receive the RFID tag data earlier. Don’t understand it though because the incoming data packet was present on respective receive pin (UART_B_RXD) as confirmed with DSO.

Perfect that it works. Thanks for the feedback.