Communicating Over The Bus - Agilent Technologies 54621A Programmer's Manual

Communicating Over the Bus

Because GPIB can address multiple devices through the same interface card,
the device address passed with the program message must include not only the
correct interface select code, but also the correct instrument address.
Interface Select Code (Selects Interface)
Each interface card has a unique interface select code. This code is used by the
controller to direct commands and communications to the proper interface. The
default is typically 7 for GPIB controllers.
Instrument Address (Selects Instrument)
Each instrument on an GPIB must have a unique instrument address between
decimal 0 and 30. The device address passed with the program message must
include not only the correct instrument address, but also the correct interface
select code.
DEVICE ADDRESS = (Interface Select Code * 100) + (Instrument Address)
For example, if the instrument address for the oscilloscope is 4 and the interface
select code is 7, when the program message is passed, the routine performs its
function on the instrument at device address 704.
For the oscilloscope, the instrument address is typically set to 707.
Oscilloscope Device Address
The examples in this manual and in the online Programmer's Reference assume the
oscilloscope is at device address 707.
See the documentation for your GPIB interface card for more information on
select codes and addresses.
Programming over GPIB
Communicating Over the Bus
3-5