FAQs from Rohde & Schwarz

HMP40x0 and 20x0 RS-232 communication


I want to control my HMP using the RS-232 port on the HO720. Unfortunately i do not get any response from the device. What do i have to do to ensure proper communication?


The HMP can be easily controlled over the RS232 port. However there are some prerequisites to be aware of. Be sure the device is set to serial Port and the RS-232 is setup correctly. See the following menus:
[Menu] - (Interface) - (Select Interface) - (--> RS232) has to be choosen

Go one step back and open (Settings) to check all the parameters to be setup correctly. For the following example the device should be set to 9k6 / 1 Stopbit / No Parity / No Handshake /

The communication parameters are 9k6 / 8N1 now.

Use a "Modem" (1:1) cable to connect the instrument to your PC.

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).

Step 1

RealTerm setup 1

Step 2

RealTerm setup 2

As you can see, the lines have been terminated with LF (/n). 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 HM8118 including the termination characters (\n ):

16:42:18.868 HMP4000: *RST\n
16:42:19.878 HMP4000: *IDN?\n
16:42:19.947 HMP4000: 68.4 ms ROHDE&SCHWARZ,HMP4040,103340,HW50020003/SW2.62