The capture window on the STU 540 takes a very long time to appear when used serially
When trying to capture signatures from the STU 540 in serial mode (e.g. over RDP) the capture window takes several minutes to be displayed
If you want to capture signatures from the STU 540 in serial mode you must use the on-board ROM images. This is known as "Signature Mode".
For further details of how to implement "Signature Mode" please see the STU-540 Operating Modes.