Setting the RS-485 Transceiver Control Mode in LabVIEW Real-Time

Setting the Default Mode of Operation

To set the default mode of operation:

• For PXI:
  
  Use the Advanced tab in Measurement & Automation Explorer (MAX) to define the default transceiver control mode.




• For FieldPoint devices supporting multiple transceiver control modes, follow these steps:
  
  

  Note  Without modification, the default mode is set to four-wire.

  1. Using an FTP client, download the /ni-rt/system/niserial.dbs file from the LabVIEW Real-Time target.
  2. Locate the entry in the niserial.dbs file that says SerialPortName = "COMx", where COMx corresponds to the port you want to modify.
  3. In the next line, add the following entry to the niserial.dbs file:
     
     TransceiverMode = <Transceiver Mode>
     
     where <Transceiver Mode> is:
     
     

     <Transceiver Mode>	Description
     128	Four-wire mode
     129	Two-wire mode: DTR controlled with echo
     130	Two-wire mode: DTR controlled
     131	Two-wire mode: Auto Control

  
  
  
  4. Copy the file back to its original location on the LabVIEW Real-Time target, replacing the original file. Reboot your LabVIEW Real-Time target for your changes to take effect.
     
     For example, to configure COM4 to use two-wire Auto Control mode, the following would appear in the niserial.dbs file:
     
     SerialPortName = "COM4"
     TransceiverMode = 131

Modifying the Transceiver Control Mode Programmatically

To modify the transceiver control mode programmatically:

• In LabVIEW Real-Time, you must use the VISA wire mode attribute to change the RS-485 transceiver control mode programmatically.