Filter
Top Products
Installation Chapter 2
GPIB-100A User Manual 2-2 © National Instruments Corporation
Grounding Configuration
A U.S. standard three-wire power cable is provided with the GPIB-100A. When connected to a
power source, this cable connects the equipment chassis to the power ground.
The GPIB-100A is shipped from the factory with chassis and power grounds connected to the
logic ground of the digital circuitry and the shields of the interfacing cables. If it is necessary to
isolate these grounds to prevent current loops between units, disassemble the unit according to the
following instructions and remove jumper W1 located on the circuit card assembly near the back
panel.
Disassembly
The case consists of two identical sections. Before disassembling, remove power from the unit.
Then remove the two screws on each side of the case and lift the top section. When reassembling,
it may be necessary to adjust the two trim panels on the case side for proper fit in their grooves.
Mounting
The GPIB-100A enclosure is designed for table top operation or for rack mounting. Single and
dual unit rack mounting kits are available from National Instruments for field installation.
Connecting to Hewlett-Packard Controllers
To achieve very high data transfer rates and long cable spans between devices, many Hewlett-
Packard (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 Not Ready For Data (NRFD) and
Not Data Accepted (NDAC) are loaded.
Preloading increases ringing on signal transitions and may cause improper operation of the GPIB-
100As. If this happens, all signals on the Master Controller should be set to normal (1 unit) load.
This is done by means of a back panel switch when working from the exterior. In addition, the
cabling rule of no more than 2m/device must be strictly enforced.