FAQs from Rohde & Schwarz

HM8123 serial communication


I want to control my HM8123 via the built in RS232 port. Unfortunately i do not get any response from the device.
What do i have to do to ensure proper communication?


The HM8123 can be easily controlled over the RS232 port. However there are some prerequisites to be aware of.

  • Use a "Modem" (1:1) cable to connect the instrument to your PC
  • The communication parameters are 9k6 / 8N1

For the first step it helps to check with a standard terminal program. We used "Realterm" here, which is available for free in the web.

When setting up Realterm we could try several commands with success (you can not see the input here - echo was off in that example):

HM8123 serial communication

As you can see, the lines have been terminated with CR (/r). It is important to also keep this settings when writing own programs.

We wrote a small program using R&S Forum Python interpreter and could control it easily. The next lines show the communication between Forum and the HM8123 including the termination characters (\r ):

12:49:48.512 HM8123: IDN\r
12:49:48.575 HM8123: 62.6 ms HAMEG Instruments,HM8123,5.12\r
The current readout is HAMEG Instruments,HM8123,5.12

Forum is available for free on our web site.