Agilent Technologies E5805A - Manual (Page 17)

E5805A USB/RS232 Interface
E5805A USB/RS232 Interface 13
In this mode, the driver identifies a converter based on the
physical USB port where it is connected. This effectively
assigns COM port numbers to physical USB ports. No matter
which converter is plugged into a given USB port, it uses the
COM port numbers assigned to that USB port. This permits a
converter to be replaced with a new unit, and, although the
new unit has a different serial number, it receives the same
COM port assignments as the old unit because they were both
plugged into the same USB port.
When using this mode, converters are not identified by their
serial number, but by a 2- 7 digit number that identifies the
USB port it is plugged into.
After changing this setting, you need to reboot before the
change takes effect.