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.

Check Hardware and wiring

Check power supply and cabling
  • Check cabling and connections from:
    1. AC Line to DC motor voltage supply.
    2. DC supply to Lexium MDrive.
  • When power is ON, LED 1 on the upper-right of the Lexium MDrive heat sink should be solid green.
Check Communications adapter and cabling – SEM MD-CC404/5-000
  • Ensure the adapter is firmly seated in the USB port of your PC or notebook
  • Verify that the DB9 is firmly seated and the screws are tightened. If M12, verify the connector is fully inserted, and the bayonet-lock is engaged.
Check Communications adapter and cabling – Third-party adapter/cable
  • Ensure the adapter is firmly seated in your PC or notebook
  • Verify that the DB9 is firmly seated and the screws are tightened. If M12, verify the connector is fully inserted, and the bayonet-lock is engaged.
  • Ensure the crossover between the interface and Lexium MDrive (Rx—Tx / Tx—Rx).
  • Using a multimeter, ring out the cable conductors to verify correct connection of all signals

Check software settings

Verify selected COM Port settings
  1. Open both the Motion Control Programmer settings dialog and the Computer’s Device Manager. Verify that the selected COM port matches what the adapter is installed on.
  2. In the device manager, right-click on the COM port, select “Properties.”
  3. Verify that the adapter drivers are operating correctly as indicated in the “Device status” text area (1). Do not close the properties dialog.
  4. Click the “Port Settings” tab of the COM Port properties dialog, verify the selected BAUD rate matches that set in the Motion Control Programmer Terminal settings dialog.
Verify Lexium MDrive settings
  1. On the Motion Control Programmer, select the menu View > Find Comm. Settings, Click Find (1).
  2. Wait while the test runs through the various BAUD Rates/Settings. If settings differ from the defaults, adjust the settings to match the Lexium MDrive.

If still unable to establish communications, perform a loop back test to identify where in the communications chain the error is occurring.

Loop-back test procedure

  1. Ensure the MDrive product is in a powered down state.
  2. Disconnect the cable from the MDrive communication port.
  3. Add jumpers as shown in the drawings below.
  4. Type characters into the terminal window.
  5. If characters now echo to the terminal screen, there is a communication problem with the Lexium MDrive product.
  6. If typed characters are still not visible, there is a problem with the adapter cable, Motion Control Programmer configuration, or personal computer communication port.

The following diagrams are oriented with the cable end facing the user.

MD-CC404-000 Communication Converters (Lexium MDrive DB9)

FIgure 1: DB9 Loop back

MD-CC200-000 or MD-CC400-001 Communication Converters

Figure 2: IDC loopback wiringiMD-CC402-001 Communication Converter

Figure 3: 10-pin wire crimp (Hirose) loopback wiring

MD-CC401-001/MD-CC405-000 Communication Converter


Figure 4: M12 loopback wiring

Party Mode Exception

If the loop back test results indicate a functioning communication link, there is still a chance that the MDrive is communicating properly, but configured in the party mode and you don’t know the device name.

The following command sequence will retrieve the MDrive’s name. There maybe no terminal feedback while typing the characters. Type: [CTRL + J]*PR[space]DN[CTRL + J]. The MDrive should return its name in quotes. Further communication then can be carried out by properly addressing the unit by name. The following command sequence will place the MDrive in the factory default state: [CTRL + J]*FD[CTRL + J]. All parameters will be replaced with the factory defaults and all programs erased. There will be no terminal feedback while typing the reset characters and the SEM copyright sign on message will be the result.