Digital Electronics: Principles, Devices and Applications

Troubleshooting Digital Circuits and Test Equipment 697Device-ATalkerD101{Data (D101 TO D108)D102D103D104Device-BListenerDevice-CTalk & ListenDevice-DTalk, Listen& ControlDAVNRFDNDAC{Data ByteTransferControl LinesD105D106D107D108DAVNRFDNDACIFCATNSRQRENEOIIFCATNSRQRENEOIGeneralManagementLines(a)(b)Figure 16.37IEEE-488 interface standard.measurements, and in the talking mode they transmit the results of measurements. A controller issupposed to manage the interface bus.The interface bus has 16 lines and uses a 24-pin connector. A maximum of 15 devices/instrumentscan be connected to this interface bus in parallel. A typical data rate is 250–500 kbytes/s over thefull transmission path which ranges from 2 to 20 m. The maximum data rate is 1 Mbyte/s. There areeight lines dedicated for data transfer (D-101 to D-108) in bit parallel format. There are three lines fordata byte transfer control (DAV, NRFD and NDAC) and five lines for general interface management(IFC, ATN, SRQ, REN and EOI). Different lines in the interface bus carry addresses, program data,measurement data, universal commands and status bytes to and from the devices interconnected in thesystem. The data lines are held at +5 V for logic ‘0’ and pulled to ground for logic ‘1’.The other popular instrument interface buses that allow interconnection of stand-alone instrumentsand computers are the VXI-bus, the PCI bus and the MXI-bus. These interface buses are more relevantto the fast-growing concept of virtual instrumentation and therefore are discussed in the next sectionon virtual instruments.16.19 Virtual InstrumentationAdvances in software development and rapid increase in the functional capabilities available on thePC platform have changed the traditional instrumentation scenario. The scene is fast changing fromthe box-like conventional stand-alone instruments to printed circuit cards offering various instrumentfunctions. These cards are inserted either into a card cage, called the mainframe, or into a PC slot. Theseacquire the measurement data which are then processed in the computer and subsequently displayed on