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I am trying to use RS232 communication to my scope and it is not working. What can I do to fix it?


I am trying to use RS232 communication to my scope and it is not working. What can I do to fix it?


The following is a trouble shooting guide which goes through the possible issues and how to fix them.

Getting Started

If you’re having communications problems between your PC and Oscilloscope this document provides the steps to help you get the communications running successfully. One of the most common complaints is “I’m getting an error message from the WaveStar program’s Instrument Manager Service that states “Device Running” and “Attached Hardware not Responding”. We will review the steps necessary to verify the hardware and software components and ultimately to get WaveStar running. You may also be having issues communicating with OpenChoice. If you encounter problems at any of the steps below, contact technical support with information on the kind of error that is occurring, and the step in the guide that it is occurring.

1.0 Verifying the Hardware

We will begin by verifying that your cable, the PC COM port, and the oscilloscope COM port are working correctly.

  1. Is your cable a Null-Modem style RS-232 cable? If you are not sure, read the section RS-232 Cable Issues. If yes then go to next step.
  2. Have the communications parameters been set properly on your oscilloscope? If you’re not sure see the sectionCommunications Parameters. You may also need to refer to the operator/users manual for your oscilloscope to determine how to set these parameters. If the parameters are set correctly go to next step.
  3. Are the COM ports on the oscilloscope and PC functioning properly? See the sections Test the oscilloscope RS-232 portand Test your PC RS-232 port

1.1 RS-232 Cable Issues

One of the most common problems with RS-232 communication is choosing the wrong RS-232 cable. There is no such thing as a standard RS-232 cable, so you may need to use an ohmmeter to verify that your cable is wired correctly. Many cables don’t have all of the pins connected. The first thing you need to know is whether the PC and oscilloscope are DTE (Data Terminal Equipment) or DCE (Data Communications Equipment) devices. This information is in the documentation provided with your oscilloscope and with your PC. Most modern Tektronix oscilloscopes are DTE devices.

If you are connecting two devices of the same type, like a modern Tektronix oscilloscope and a modern PC, you need a null modem cable. This is a cable whose lines are crossed such that the inputs of one device are connected to the outputs of the other.

Confirm that your cable is a null-modem cable as follows.

  • 2-3
  • 3-2
  • 4-6
  • 5-5
  • 6-4
  • 7-8
  • 8-7

Short pins 1&8 at each end of the cable.

This cable is available from Tektronix under the part number 012-1379-00.

If you are connecting a DTE device to a DCE device you will need a straight-through cable. This is a cable that has the same pin assignments on both ends of the cable.

CAUTION: Do not connect the output lines of two same-type devices to each other. Doing so may damage one or both of the devices.

For hard flagging to work, the RTS (Request To Send) and CTS (Clear To Send) lines must be connected. Use an ohmmeter to verify that they are actually connected since not all cables connect these lines. The RTS line is sometimes referred to as RFR.

WaveStar does not use the DCD (Data Carrier Detect) so it does not matter whether or not it is connected. The DCD line is sometimes referred to as RLSD.

1.2 Communications Parameters

Make sure the communication parameters are set correctly on the oscilloscope and the PC program.

Baud rates should be the same on both the oscilloscope and the PC. Parity should be None, Data Bits should be 8, and Stop Bits should be 1. Do not use baud rates above 9600.

Soft flagging should never be used for waveform and hardcopy transfers. This is because waveform data and hardcopy output contain binary characters, which can easily include the XON and XOFF characters, used to implement soft flagging. Soft flagging should only be used for transferring stored setups since stored setup information generally consists of printable ASCII text.

Although it generally should not matter if the EOL characters are the same, it is typically recommend that you set the EOL to CRLF to be sure there are no problems.

Hint: In the RS232 setup menu of the scope select Default RS232 button if available. This will result in a good starting point.

1.3 Test the oscilloscope RS-232 port:

The following steps will allow you to verify the performance of the RS-232 port on your scope.

  1. Short pins 7 & 8 on the end of the 9 pin cable that would connect to your PC.
  2. Connect the scope probe to the channel 1 BNC connector on your scope.
  3. Connect the probe tip to pin 2 and the ground clip to pin 5.
  4. Set the hardcopy port on the scope to RS-232.
  5. Set the scope volts/div to 5 Volts.
  6. Set the scope time/div to 500us.
  7. Press the hardcopy or print button on the scope.
  8. You should see a stream of square wave pulses as the hardcopy data is sent out the RS-232 port.

If the test of your oscilloscope port is successful then go to the next step to confirm the function of your PC's RS-232 port. If your oscilloscope fails to output data you should contact Tektronix service to arrange for repair of the product.

1.4 Test your PC RS-232 port:

Using a terminal program such as Windows Terminal, HyperTerminal, Crosstalk, etc. you can test the RS-232 port on your PC. At this step you will setup a terminal program to receive data from the selected COM port and display on your PC screen. The data will be the hardcopy output that we verified in the previous step was transmitting out of the scope.

At the time of writing this file we used Windows HyperTerminal 1999 on a Windows 2000 PC. Specific steps for using HyperTerminal are listed next. To learn how to use your specific terminal software, refer to the documentation for the product or contact the software vendor.

2.0 Steps for running HyperTerminal

  1. To run the program click on the Windows Start button, select Programs > Accessories > Communications > HyperTerminal.
  2. The HyperTerminal program launches with a spinning globe logo. A popup dialog screen appears asking for the name and icon. This is used if you plan to save a communications session. Since you won’t need to save the session just type anything in the name field and don’t worry about the icon. Click on the OK button.
  3. A popup dialog box titled “Connect To” appears. At the bottom of the box is a field titled “Connect using:”. Click on the arrow to the right side of the field and choose your COM port. (On most laptop PC’s there is only one COM port and it is typically numbered COM1. Click on the OK button.
  4. A popup dialog box titled COM<x> Properties appears. The value for <x> will match the COM port number you selected in step 3.
  5. Click the arrow at the right side of the Bits per second field and change the rate to 9600. The rest of the properties, 8, None, 1 and Hardware should already be set. Click on the OK button.
  6. At this point the HyperTerminal window will either clear leaving a blinking cursor in the upper left corner or an error message dialog box may appear. The message may read: “Unable to open COM<x>. Please check your port settings”
  7. If the screen clears go to step 9. If you see the error message then you will need to determine why your com port won’t open.
  8. If you got the error message, this is typically due to some other application such as the HotSync program installed for a Palm Pilot or other PDA. You can check the Windows Task Manager Processes list to see if “hotsync.exe” is running. If it is, end the process and go back to step 1. If you’re not sure about applications using your COM port you may be able to get assistance from your company computer support staff or from your PC vendor technical support in determining what application is preventing access to the COM port. Keep in mind that as long as the COM port is not available to HyperTerminal it will also not be available to WaveStar or OpenChoice. If the WaveStar Instrument Manager was started previously, it may still be using the COM port. The Instrument Manager Service continues to run as a background task even after the Instrument Manager control panel has been closed. To check on this, reopen the Instrument Manager, open the “Control” menu and select “Shutdown Service”. Return to Step 1 of this section.
  9. (NOTE: In this next step you will not see the characters echo on the Hyperterminal screen. This can be changed by going into Hyperterminal menu File > Properties > Settings > ASCII Settings and check the box labled Echo typed characters locally)

Type the characters *IDN?, hit the Enter key. The oscilloscope should respond with its identification string. This string will look similar to this:

TEKTRONIX,TDS 2024,0,CF:91.1CT FV:v4.12 TDS2CM:CMV:v1.04

This concludes the troubleshooting guidelines. If you have successfully completed the steps above, you have full communication with your oscilloscope through the RS-232 port. You should now be able to restart WaveStar and establish a connection. The following steps provide a quick getting started with WaveStar guide. Please refer to the WaveStar Users Manual for complete instructions on that products use.

3.0 If you’re using the Tektronix WaveStar program:

The first step in running the WaveStar program is to establish the connection to the oscilloscope using the Instrument Manager.

  1. Start Instrument Manger from the WaveStar folder
  2. Select the Edit menu then Add Instrument.
  3. From the pull-down list, choose your instrument type
  4. A list of available ports will appear.
  5. Select the proper COM port. (COM1 = ASRL1 and COM2 = ASRL2)

4.0 Check the Instrument Manger Status

The status should read:

SW Status HW Status

Running Responding

If you get a status that reads:

SW Status HW Status

Running Not Responding

There may be an error in the installation of WaveStar. Try uninstalling and reinstalling WaveStar. If TekVISA does not show an RS232 port, i.e. ASRL1::INSTR, check that the search for serial is enabled. Verify that TekVISA has been installed and was not overwritten by another vendors VISA. You can do this by searching for the file visa32.dll and right click on it to see its properties.

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