RS-422/485 MDrive products can appear to have a communications failure when it is merely in a mode that prevents it from responding to or echoing back, instructions in SEM Terminal.

Settings that can cause this include

  • Party Mode (PY=1)
  • Checksum (CK=1)
  • Echo Mode (EM=1or2)
  • Incorrect Baud Rate (BD)

Also, check the scroll bar in the terminal window. If it is not all the way down, you may not see what the driver sends back.

When you have communications problems, the simplest fix may be to set your driver back to factory defaults using the instruction “FD”. To prevent defaulting all the drivers in your system, you may want to plug your communications cable into only the driver you are working on.

Make sure that you have a backup copy of the all variable settings and program before doing this.

By inserting a string of text into one of the function keys in a Terminal window in SEMTerminal, it can be sent to the driver as a continuous string of characters:

(copy / paste string above) To do this, open SEM Terminal and click on the terminal window. If there is no terminal window open, open one using View > New Terminal Window.

Figure 1: Terminal window showing function key group

Right-click on the function key area at the bottom of the terminal window. The function key setup dialog will open.

Figure 2: Function key setup dialog
Pick one of the function keys and type something like “Reset FD” into the Caption. Then highlight, cut and paste the character string given above into the Contents window of that row and click on Done. When that function key is pressed, the string will be sent. Note that there are delays in this string and it takes about 4 seconds to complete. When you are able to communicate with the driver, type “S” then a carriage return. This will save the defaults.

If you still haven’t established communications, try setting SEM Terminal to different baud rates. This is done by Right-clicking the text area of the terminal window and select Preferences.

Figure 3: Terminal settings dialog
Figure 3: Terminal settings dialog

 

Then select the Comm Settings tab. Select the baud rate desired and make sure that the radio button for MDrive is selected. Select Done, then try your function key. You may have to try all the possible baud rates.

Example LabVIEW Libraries for Lexium MDrive assist in prototyping and development by providing easy access to common MCode motion and I/O functions.