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How to Use PORTTEST

The PORTTEST diagnostic applies only to OmniTurns equpped with a PLC, either in a ZipLoader or installed in the machine as Expanded I/O.
Image of Failled Communications Prompt

If the CNC control 'hangs' on a command to the PLC, and displays the error "Failed PLC Communications..." after pressing the Esc key, you may need to run PORTTEST to determine the cause of the problem.

  • First, verify that you have power to the PLC.
  • Next, check all cables between the CNC and the PLC.
  • Then, unplug and replug the connectors to and from the RS422 converter in the CNC, and the DIN connector at the PLC.

If you have power and the connections are good, and you unplugged and replugged the cables, the next step is to run PORTTEST.

PORTTEST is a simple app installed on the OmniTurn to test the communication port that the CNC uses to 'talk' to the PLC.

  • With CNC power off, first disconnect the cable to the PLC at the CNC and a connect the RS422 loop‑back connector.
  • Power up the CNC and drop to DOS.
  • At the K:\CNC prompt type PORTTEST, then press Enter.
  • Press the number that corresponds to the port your PLC is connected to (either COM2 or COM3 depending on motherboard), then press any key.
    NOTE: G3 PORTTEST choices are different: select 3.RS422(expanded I/O) port
  • The test will respond COMx is OK or Waiting for response, then Test failed.(On G3 CNC the prompt sticks at "Waiting for response"; this means test fails. Press Esc key to continue).
If the port is OK, the issue is downstream, towards the PLC; if the port fails, then the issue is upstream, towards the motherboard.

If the port fails, run PORTTEST at the motherboard using the 9 or 25 pin loop‑back connectors that shipped with the PLC or loader. Set the CNC power off, disconnect the ribbon cable that is attached to the RS422 converter, put the loop‑back connector on the ribbon cable and run PORTTEST again.

Below are illustrations and captions describing the entire process.
Image of RS422 loop-back connector
This is the RS422 loop‑back connecter. One of these is shipped with every PLC-equipped GT, every ZipLoader and every PLC Expanded I/O kit. Connecting this to the CNC control is the first step in the porttest procedure. Replacement loop-back connector can be ordered.
Image of RS422 loop-back connector
This is the RS422 loop‑back connecter installed on the CNC control. Remove the cable that connects the CNC to the PLC at the connector labeled "PLC", and attach the loop‑back connector. The RS422 converter is powered by 5VDC from the PLC, so it is necessary to provide 5VDC from another source. There is at least one spare 4-position Molex connector available near the back corner of the control. The CNC control "wedge" is attached to the top the the GT with four 3/8-16 SHCS. Remove three of them, leaving the rear right-hand one so the control can be pivoted as shown in the photo. Remove the blue cover and connect the spare Molex connector to the loop‑back power cable.
Image of G4 OmniTurn Splash Screen
G4 CNC: When the control boots up to the File Backup prompt, press Ctrl-C instead of y or n and you will drop to the DOS prompt, which will be K:\CNC>

(These are G4 CNC screens; for G3 screens click here)

Image of K:\CNC DOS Prompt
At the K:\CNC> prompt, type: p3test then press Enter. The p3test app will display the PLC port number, either COM2 or COM3.
Image of p3test results
When the p3test app displays the PLC port number, either COM2 or COM3, note which it is because that is the COM port you will select in the next step.
Image of K:\CNC DOS Prompt with porttest
At the K:\CNC> prompt, type: porttest then press Enter. The PORTTEST app should open.
Image of G4 CNC PORTTEST app with Install loopback
In the PORTTEST app, select #2 or #3 depending on your PLC port; you will be prompted to install loop‑back connector, which you've already done.
Image of porttest results

The results will be "Test failed" or "COM3 (or COM2) is OK".

If failed, the next step is to repeat the PORTTEST at the input of the RS422 converter to see if that's the culprit.

If OK, the next step is to repeat the PORTTEST at the input of the PLC using the Mini‑DIN loop‑back connector.

Image of G4 OmniTurn Splash Screen

G3 CNC: When the control boots up to the File Backup prompt, press Ctrl-C instead of y or n and you will drop to the DOS prompt, which will be C:\OMNITURN_

Image of G3 CNC drop to DOS
vAt the C:\OMNITURN_ prompt, type: porttest then press Enter. The PORTTEST app should open.
Image G3 CNC PORTTEST app with install loopback
In the PORTTEST app, select #3 for RS422 port; you will be prompted to install loop‑back connector, which you've already done.
Image of G3 CNC PORTTEST results
The results will be "Waiting for response" or "RS422 port at COM2 is OK".

If waiting, press Esc key. The next step is to repeat the PORTTEST at the input of the RS422 converter to see if that's the culprit.

If OK, the next step is to repeat the PORTTEST at the input of the PLC using the Mini‑DIN loop‑back connector.

Image of DB9 and DB25 loop-back plugs
If PORTTEST at the PLC connector on the rear panel of the CNC fails, the RS422 converter may be the culprit. Early PLC installations used a 25-pin converter, and later installation used a 9-pin converter. The converters are connected to the COM port on the motherboard with a ribbon cable. To test the input to the converter, a 9 or 25 pin loop‑back connector is required. These ship with every PLC installation, either in the CNC control, spindle electronics cabinet, or PLC cabinet.
Image of DB9 loop-back plug connected
The RS422 converter is mounted in the CNC control, right behind the monitor. Its input is via ribbon cable from the motherboard; its ouput is via descrete wires to the PLC connector on the rear panel of the CNC. Disconnect the ribbon cable from the converter and connect the loop‑back plug. Power up the CNC, drop to DOS as before and run PORTTEST as before.

Click here to go back to the instructions for G4 CNC.

Click here to go back to the instructions for G3 CNC.

If the Test passes, then the motherboard/ribbon cable connection is good, and the converter may have failed.

Reconnect the ribbon cable and repeat PORTTEST at the PLC connector on the rear panel; if the test fails, replace the converter: 9-pin or 25-pin
If it passes this time, the issue was solved by disconnecting and reconnecting cables.

Image of Mini-DIN loop-back plug connected
If PORTTEST at the PLC connector on the rear panel of the CNC passes, the cable between CNC and PLC may be the culprit, or (less likely) the PLC may have failed. Connect the mini-DIN loop-back connector to the PLC as shown below.

If the Mini‑DIN loop-back connector is not available, carefully examine the cable between CNC and mini‑DIN connector at PLC. This wiring diagram shows pin numbers to ring out.

Image of Mini-DIN loop-back plug connected
This is the Mini‑DIN loop‑back connector connected to the PLC.

Power down the CNC and disconnect the mini‑DIN connector from the PLC and plug it into the female loop‑back plug. Plug the male end of the loop‑back connector into the PLC.

Power up the CNC, drop to DOS and run PORTTEST as before. If necessary, go back to the instructions for G4 CNC, or G3 CNC.

If the test passes, then the cables are good, and the PLC may have failed. Power down the CNC. Remove the loop‑back connector and reconnect the DIN cable, and see if you can communicate with the PLC. If so, disconnecting and reconnecting the cables solved the problem; if not the PLC is probably bad.

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