Connection Chapter 2
GPIB-120A User Manual 2-2 © National Instruments Corporation
Placing Your Instruments
Identify the instruments or devices in your system that are sensitive to ground loop noise. In the
next section, Connecting the GPIB-120A, you will connect these instruments or devices to Bus B
of your GPIB-120A. Then, you will connect the other instruments or devices to Bus A. Usually
you connect your computer or other device acting as the GPIB System Controller to Bus A.
Connecting the GPIB-120A
To connect the GPIB-120A, follow these instructions:
1. Make sure that the power switch on the back panel is in the off position.
2. Plug the utility power cord into an acceptable electrical outlet (100 to 120 VAC or 220 to
240 VAC, depending upon which model of the GPIB-120A you have). Plug the other end
of the power cord into the back panel of the GPIB.
3. Link your GPIB instrument(s), board(s), and other device(s) to the GPIB-120A with
appropriate cables (type X1 or X2). Use Bus A for devices that do not need to be electrically
isolated. Use Bus B for devices that need to be electrically isolated from devices on Bus A.
4. Move the power switch to the on position.

Connecting to Hewlett-Packard Controllers

To achieve very high data transfer rates and long cable spans between devices, many HP
Controllers and computers, such as the 64000 series, use a preload technique on the unit
designated Master Controller. When preloaded, the GPIB lines of the Master Controller are
terminated to represent six device loads. HP has two types of preloading: Class A, in which all
16 GPIB lines are loaded, and Class B, in which all lines, except NRFD and NDAC lines, are
loaded.
Preloading increases ringing on signal transitions and can cause improper operation of the
GPIB-120A. If this happens, set all signals on the Master Controller to normal (1 unit) load.
This is done using a back panel switch on your HP Controller. In addition, you must also strictly
conform to the cabling rule of no more than two meters per device.
Mounting the GPIB-120A
The GPIB-120A is designed for table-top or rack-mount operation. Single- and dual-unit
rack-mount kits are available from National Instruments. Refer to the Optional Equipment
section of Chapter 1, Introduction, for ordering information on the rack-mount kits.