The bus address is the number corresponding to the switch settings on
the I/O card.  Normal HP-IB bus addresses range from 0 to 30, with bus
address 31 being an illegal bus address.  Bus address 31 is reserved
for the Device I/O Library (DIL).

Please enter an integer between 0 and 7 for a CS/80 device, and an integer
between 0 and 30 otherwise.
