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RS485 Flow control on ColdFire 54415

Question asked by Nicolas UHL on Jun 3, 2014
Latest reply on Jun 19, 2014 by soledad


I'm developping an application on Coldfire 54415 with MQX.

I need to implement the RS485 protocol with "RS485 flow control". Meaning that I need to pull the RTS line low during the transmission.

In MQX, when we deal with the serial port, it should be possible to use the IO_SERIAL_HW_485_FLOW_CONTROL flag.

But it seems it does not work with this Coldfire. I went inside the serial driver from MQX. This flag is not managed.

I also tried the following way, to check how the ioctl flags work:

    flag = IO_SERIAL_RTS;

    ioctl(ACM_Tty[idx].fdev, IO_IOCTL_SERIAL_SET_HW_SIGNAL, &flag);


This is supposed to be managed by the UART driver in MQX.

But nothing happens on the RTS line.


So, what is the way to manage automatically the RTS line in "RS485" mode.


I know that I could handle the RTS manually with GPIO but this is too slow (I communicate with a slave device that replies very fast. So I need to release the RTS line as soon as the transmission is complete).


Thanks in advance.


Best regards