L3Harris narda PMM EP-600 User Manual page 61

The user can quickly change the desired communication channel by
clicking onto the Comm port drop-down menu.
When the menu is selected, the communication port selector appears. It
allows the user to choose between the RS232 port or RS232-to-USB
converter that is needed if no RS232 port is available in the controller PC.
When the USB connection is used, the USB-RS232 adapter appears
among the devices as a "Prolific USB to Serial Comm Port (COMn)".
Click on RS232 to confirm.
Then, the main window is displayed together with the WinEP600 -
Connection Incoming indication of the correct communication with the
probe.
WinEP600 and SetAddEP600 operating instructions 5-7