Data Acquisition

• Count method – Using the count method requires that the controller stop thetalker from sending any more bytes once the specified number of bytes hasbeen sent to the listener. This can be achieved by asserting the NRFD andNDAC bus control lines, but requires the application software for the GPIBcontroller hardware to control this facility.Assuming the GPIB has been initialized and configured correctly, the protocols forsending and receiving data are as follows:1 Set ATN ‘true’ and EOI ‘false’.2 Send the controller talk address.3 Send the UNL command message.4 Send the listen address for each device to be configured as a listener.5 Set ATN ‘false’.6 Send the required data bytes one byte at a time.7 Send the terminating character or set EOI ‘true’.1 Set ATN ‘true’ and EOI ‘false’.2 Send the UNL command message.3 Send the controller listening address.4 Send the required talker address.5 Set ATN ‘false’.6 Receive data bytes until terminating character received or EOI ‘true’.8.8 IEEE 488.2IEEE 488.2 was drafted to correct problems that arose with the original IEEE 488standard. At the same time, it was designed to ensure compatibility with existing IEEE488.1 devices. The concept used in expanding the standard was that the manner, in whichcontrollers and instruments would function as talkers, would be precisely defined. Thismeans that fully compatible IEEE 488.2 systems would be reliable and efficient.However, backward compatibility with IEEE 488.1 devices could be ensured bydesigning the standard so that IEEE-488.2 devices, when acting as listeners, would beable to accept a wide range of commands and data formats from IEEE 488.1 devices.The IEEE 488.2 standard sets out a number of requirements for a controller, including anexact set of IEEE 488.1 interface capabilities as follows:• Sensing the state and transitions of the SRQ line• Setting and detecting EOI• Pulsing the interface clear line for 100 microseconds• Setting/asserting the REN line• Timing out on any I/O transaction