How to use “Talk only mode” of Digital Multi Meter 34401A.

August 11, 2021

Have you ever wished that you could save data to a PC while using a DMM (Digital Multimeter)? In fact, some DMMs can send measured data to a personal computer without using special equipment or software.

Use the DMM’s “Talk Only Mode" for this. Such features are common in bench-type DMMs from my experience. If you want to use talk-only mode, look at the back panel of the DMM. If there is SR-232C port, it is possible with high probability.

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34401AはRS-232 と書いてある 9ピン2列のオスならばOK

In this article, I will use Keysight (formerly Agilent Technology) 's classic multimeter 34401A. When using the talk-only mode of the 34401A, prepare the 34401A in talk-only mode, a PC with a serial port, and a serial reverse cable.

Let’s take a look at the DMM, PC and cable.

Configuration of 34401A

The 34401A has a GPIB port and an RS-232 port. Which port to use for communication must be set on the front panel of the 34401A. This time, serial communication is performed using the RS-232 port, so set the output destination to the RS-232 port as follows.

Shift button <button E: I / O MENU V button 2: INTERFACE V button RS-232 Enter button

With the above settings, the 34401A can be controlled with the RS-232 port and the serial port of the PC. If you do not send a command by serial communication, the 34401A will not operate unless you keep this, so set to talk-only mode.

Shift button <button E: I / O MENU V button 1; HP-IB ADDR V button 31: TALK ONLY Enter button

With this setting, the measurement result is always transmitted from the serial port. Let’s connect this measuring instrument to a personal computer.

Connect to PC

When connecting to a PC, prepare a serial reverse (cross) cable. Usually, a serial cable is a straight cable, but the connection between devices uses a reverse cable.

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A straight cable is used to connect a communication device such as a modem to a personal computer. In the past, there was one in the family. Be careful as serial cables on the market are overwhelmingly straight.

PC settings

Lastly, let’s talk about PC settings.

Obviously, please prepare a personal computer with a serial port. But recent PCs do not have a serial port, so a serial cable that can be added via USB is OK.

If the cable driver is installed, is it working? Check which port is assigned. Check the device manager of Windows settings, there is a device with a name like “UBS serial adapter" in the column of “port (COM and LPT)", and if it is recognized without problems, write parentheses after the name Has a COM number written on it.

Next, install a terminal emulator that can perform serial communication. Older Windows had a terminal emulator called Hyper Terminal, but with the evolution of Windows, it became unnecessary and was not preinstalled from around 7.

So here we install “Putty", one of the major terminal emulators.


Download the installation file and install it. There is no particularly difficult part.

After installation, try to run. After execution, set the same speed (baudrate) as the 34401A by serial communication.

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If communication does not work, change the COM port number.

If everything has gone well, the data will be displayed on Putty’s screen.

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The displayed data can be pasted to WordPad etc. by selecting and copying on Putty.

The data displayed on Putty is the data measured by the 34401A. Therefore, if you want to switch functions such as voltage and current, set them on the front panel of the 34401A. The range and sampling rate are also set on the 34401A.


In this article, I explained how to connect a DMM to a PC with a serial cable without using any special software or equipment, and send the data measured by the DMM to the PC.

Since this method does not use a special program, it is easy to use even for those who are not familiar with instrument control. Please refer to it when you need to save data suddenly.