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Application Note

Troubleshooting Serial Port Problems

If you have trouble getting your PlanWheel PC to work with your computer, go through this checklist to find the problem.

Checking Your Installation

(Note - Scalex also manufactures the Plan Wheel manual scaler. PlanWheel does not work with a computer. Be sure your scaler is a Plan Wheel PC.)

Have you installed the scaler's batteries?

The PlanWheel PC comes with two AAA batteries. The batteries must be installed for it to work with your computer. (Be sure to remove the plastic cover from the batteries and observe the proper polarity.) Once the batteries are installed, the display on the Plan Wheel PC will turn on.

Have you plugged the scaler into the computer correctly?

The PlanWheel PC should be plugged into one of your computer's serial ports. This is straightforward, since the cable supplied with the scaler only mates with a serial port. The serial ports on your computer are the 9-pin or 25-pin male jacks. This means the serial ports have pins sticking out from the computer. The scaler will not work with any other connection.

Be sure that the cable is plugged securely into the scaler, too, and locked with a quarter twist.

Have you tried all four COM port settings?

Next, be sure you have set the "COM" port setting in your software.

No matter which software program you are using to communicate with the PlanWheel PC, you must tell it which COM port the scaler is on. Do this by trying all possible settings in turn to see which one works. Even if you think you are sure which COM port the scaler is plugged into, try all the possible settings.

If you are using Scalex Ready Connect software, click on Options > Communications. The four COM ports are shown with a bullet next to the one currently selected. Click on each port in turn, then on OK. When you choose the correct port, the values from the scaler will appear on the main window of Ready Connect after a slight delay of two or three seconds.

If you get an error message, it indicates that Windows is not allowing you to use the selected port for the reason shown. This could be that there is no such port, or that the port is already being used by other software (for example, you can't choose the mouse port if Windows is already using it for the mouse).

If, on the other hand, when you click OK you see the message "SCALER NOT RESPONDING", this means that Windows does recognize your selection as a valid COM port but that the scaler cannot be sensed on that port. You may have selected a different port than the one the scaler is plugged into or there may be a problem with the port, the cabling or the scaler.

If you are using another company's software with the Plan Wheel PC, you should also try all COM port selections. The specifics on how to do this will be found in the software's documentation or you should call technical support for the company

Have you tried all available serial ports?

If you have more than one spare serial port, try the scaler on each one in turn. Each time you plug the scaler into a different port, try all COM port selections again to be sure you are not overlooking the correct setting.

Special note for laptop owners

If you are using a laptop, it is possible that your serial port is configured as a "hot" mouse port. In other words, your serial port may be set up so that a mouse can be plugged in at any time and used in addition to the trackball or touchpad. If your port is set up this way, it cannot be used with the scaler. Consult your computer's manual or call the company's technical support to determine how to disable this feature and return the serial port to normal operation.

Localizing the Problem

If you have checked your installation and your scaler is still not communicating with the computer, then there is a malfunction in either the computer or in the scaler. The problem could be a hardware failure in the serial port, the cabling or the scaler. Or, more likely, it is a problem with the computer's configuration. Common configuration problems are serial ports which share the same interrupt as another device, serial ports which are disabled internally, Windows settings which do not match the serial port, and so on.

You may be tempted at this point to change the serial port settings in the Windows Control Panel. We recommend you do not change any port settings because this may aggravate the problem. A simple test of the serial port should be done first.

Testing the Serial Port

A quick test will tell you whether the problem is in the serial port or the scaler. To make this test, you will need a known good serial mouse.

You can use your computer's own mouse for this test if it is a serial type mouse. Otherwise borrow a serial mouse from another computer temporarily. (A serial mouse has a 9-pin serial plug. If the mouse has a round plug, it is a "bus mouse" and can not be used for this test.)

You can use your computer's own mouse for this test if it is a serial type mouse. Otherwise borrow a serial mouse from another computer temporarily. (A serial mouse has a 9-pin serial plug. If the mouse has a round plug, it is a "bus mouse" and can not be used for this test.)

If the port you want to test is a 25-pin port, you will need to connect the 9-pin serial mouse through an adapter. You can use the adapter which comes with recent models of the scaler. (If you don't have the adapter, or if your scaler is an older model, you can get one at a computer store or Radio Shack.)

To do the test, first shut down Windows and turn the computer off. Then, disconnect the regular mouse from the computer. Connect the serial mouse to the serial port you are testing, then turn the computer back on. Windows will check all serial ports for the mouse. If Windows does not find the mouse, it will display an error message. The port is not functioning properly.

On the other hand, if Windows turns on properly, the port is good. Check carefully, however, for any error messages which may appear. If there are any programs set to run automatically at startup and which use the serial port, they may now find it unavailable and display an error message.

If the port has tested good and no error messages appear, then the scaler, cable or adapter is probably defective. Contact Scalex Technical Support to arrange to have the scaler repaired or replaced.

More Help

If you need more help understanding this application note, or if a situation arises which does not seem to be covered, please contact Scalex Technical Support at 800-653-3532, from within the U.S. and Canada, or via fax at 760-633-1676. You may also e-mail