Beijer Electronics (formerly QSI Corporation)

Can't get RS-422 to work
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Author:  Entegris [ Thu Oct 28, 2010 1:52 pm ]
Post subject:  Can't get RS-422 to work

I have an application on the G58 where it works fine in RS-232 mode but I use the start-setup to change it to RS-422 and I can no longer get it to work (connected to a different 422 device and cable of course).

I can see where my device is getting the command ok and sending a response and I can scope the response signal on the cable but my application isn't seeing it. I tried swapping the Rx+ and RX- but still no joy.


1. Do I need to do anything else special in my application to use 422?

2. I am getting an error on startup: "SetCTS: Hardware currently in use (#144)" Is this significant?



Author:  Ron L. [ Thu Oct 28, 2010 2:06 pm ]
Post subject:  Re: Can't get RS-422 to work

1. There isn't anything else special you would need to do in your application. If you are changing the serial port setting at run-time you may need to reboot the terminal for it to take effect.

2. In 422 mode the hardware flow control lines are not available. That is why SetCTS is throwing an error.

Make sure that the pinout you're using matches what is documented in section 5.2.1 in the Hardware Manual.

Author:  Entegris [ Wed Nov 03, 2010 2:12 pm ]
Post subject:  Re: Can't get RS-422 to work

I still can't get it to work. there definitely is no additional setup to get receive to work?

on a similar not, I can't find where I can change the port mode (232, 422, etc) in the programmer's pdf. is this only changed on the terminal setup screen and not in my program?



Author:  Ron L. [ Wed Nov 03, 2010 2:22 pm ]
Post subject:  Re: Can't get RS-422 to work

Can you verify the model number of your G56?

Assuming the G56 has the multi-port option, you can change it in "Power On Setup" or in the code using the function SetSystemSettings (see "Help->Object Documentation" or F1 for documentation). The code would look like this:

SetSystemSetting(SYS_SAVE, true, SYSACT_DONOW) 'Save and reboot (required)

If you cannot get the 422 to work, you are welcome to return the unit for testing and possible repair. Here is the form to fill out for that.

Author:  Entegris [ Thu Nov 04, 2010 7:13 am ]
Post subject:  Re: Can't get RS-422 to work

I have a G58 with a battery. G58B?

I should have a 422 port? Does your code snippet still apply to the G58?


Author:  Ron L. [ Thu Nov 04, 2010 8:02 am ]
Post subject:  Re: Can't get RS-422 to work

Yes, the code works on a G58 also.

Author:  Entegris [ Fri Nov 12, 2010 9:35 am ]
Post subject:  Re: Can't get RS-422 to work

I still haven't got this to work.

Does the terminal have any settings or assumptions on duplex? Typically 422 is full duplex and that is how I have my cable. My protocol is half-duplex and I could try 485 but then the hardware DOES have to control the transmit. Does it also suppress the receive reflection?

My protocol is command/response and includes a 1 mS turn-around delay before a response is sent.

Do you have any suggestions for debugging? RS-232 mode works fine so my terminal software is "correct" unless I need to enable/disable or do something special for 422 (besides enabling the mode). I have scoped the signal as far as the hirose connector so I know it is going into the terminal. I also tried swapping the +/- on the receive line but that didn't help.

Author:  Jeremy [ Fri Nov 12, 2010 9:41 am ]
Post subject:  Re: Can't get RS-422 to work

422 is full duplex and the terminal is aware of that and is perfectly happy to allow simultaneous transmission and receipt of data.

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