ibpad() sets the GPIB primary address to pad for the device or board specified by the descriptor ud. If ud is a device descriptor, then the setting is local to the descriptor (it does not affect the behaviour of calls using other descriptors, even if they refer to the same physical device). If ud is a board descriptor, then the board's primary address is changed immediately, which is a global change affecting anything (even other processes) using the board. Valid GPIB primary addresses are in the range from 0 to 30.
The value of ibsta is returned.