GPIB, or General Purpose Interface Bus, instruments offer test and manufacturing engineers the widest selection of vendors and instruments for general-purpose to specialized vertical market test applications. GPIB instruments are often used as stand-alone benchtop instruments where measurements are taken by hand. You can automate these measurements by using a PC to control the GPIB instruments.
Use instrument drivers and the VISA VIs to control GPIB instruments. When you use the VISA VIs, you need to know the instrument address. Use the VISA resource name control or MAX on Windows to verify communication with the instrument and determine the instrument address. You also need to know the command set for the instrument. Most instruments use SCPI, or Standard Commands for Programmable Instruments: a single, comprehensive command set suitable for all instruments. Refer to the NI Developer Zone for more information about common instrument commands and protocols.
The GPIB protocol categorizes devices as controllers, talkers, or listeners to determine which device has active control of the bus. Each device has a unique GPIB primary address between 0 and 30. The Controller defines the communication links, responds to devices that request service, sends GPIB commands, and passes/receives control of the bus. Controllers instruct Talkers to talk and to place data on the GPIB. You can address only one device at a time to talk. The Controller addresses the Listener to listen and to read data from the GPIB. You can address several devices to listen.
The GPIB is a digital, 24-conductor parallel bus. The GPIB uses an 8-bit parallel, byte-serial, asynchronous data transfer scheme, which means that whole bytes are sequentially handshaked across the bus at a speed that the slowest participant in the transfer determines. Because the unit of data on the GPIB is a byte, the messages transferred are frequently encoded as ASCII character strings. Refer to the GPIB documentation for more information about the hardware specifications of GPIB devices.
You can obtain faster data rates with HS488 devices and controllers. HS488 is an extension to GPIB that most NI controllers support.
Refer to the NI Developer Zone for more information on communicating with GPIB instruments.