Working with RS-485 and UART-16450 on devc-ser8250

QNX USERS QNX6 - OS
1

Is a standard devc-ser8250 can work with RS-485 interface?
It is using motherboard Advantech PCA-6773 with UART-16450. Port COM2 work in RS-485 mode.

2

Should work

3

I had a 4 port serial card with interrupt share , with one of the ports using RS-485, it worked for me. Have a loopback cable set up and test it out !.

4

Warning some RS-485 card required the CTS line to be activated to take owner ship of the serial line. The QNX driver doesn’t automaticly handles this. You either need to create a custom version of the driver or handle CTS yourself (which can be tricky).

Some RS-485 card will however have the circuit that does this automaticaly.

5

int fd = open(“dev/ser2”,O_RDWR);

// This code work correctly 
write(fd,Command,sizeof(Command));

 //set the RTS to enable reading from serial port with RS- 485

data = _CTL_RTS_CHG | _CTL_RTS;

devctl (fd, DCMD_CHR_SERCTL, &data, sizeof(data), NULL);

[color=red] //This code don’t work. There is no errors, but data from serial port
//not reading.
read(fd,cReplyBuffer,sizeof(cReplyBuffer));

Anybody know why?

6

Maybe I’m not correct, but you don’t need to set RTS - driver do this for you.

7

It isn’t work if I set RTS and unset DTS and if I don’t set RTS.
Maybe I’m incorrectly set the flags or it is need to set other flags?

8

I see some sourcess (not my):

Open port;
Set RTS - like you do - _CTL_RTS_CHG | _CTL_RTS;
write command;
Unset RTS - _CTL_RTS_CHG | 0;
Read data from port.

This should be work!

9

How to read the state of register of COM-port?