National Instruments GPIB-232CV User Manual

Also see for GPIB-232CV: User manual

Contents

National Instruments GPIB-232CV User Manual Manual pdf 34 page image

Operation Chapter 3GPIB-232CV User Manual 3-4 © National Instruments Corp.Conditions that Assert SRQWhen the SRQ feature is enabled, one of the conditions that causes aservice request is when the GPIB-232CV serial input buffer is empty.Then, the GPIB-232CV receives a serial character to be sent along to theGPIB. The SRQ* signal is asserted to alert the GPIB Controller that theGPIB-232CV has data to send to a GPIB Listener. The GPIB-232CV canthen be addressed to talk so that the data can be read out of theGPIB-232CV serial buffer. After all data has been read, the Controller canunaddress the GPIB-232CV to talk so that other devices can be addressed totransfer data on the bus.The other condition on which SRQ* will be asserted, if enabled, is whenthe GPIB input buffer becomes empty. If very large amounts of data aresent over the GPIB to the GPIB-232CV (greater than the GPIB buffer size)and the serial device is a very slow data acceptor, the GPIB-232CV internalGPIB data buffer might become full. If this does occur, the FULLindicator on the front panel will illuminate and the GPIB transfer rate willslow to approximately the same rate as the serial device accepting the data.Since the maximum data transfer rate on the GPIB is only as fast as theslowest Listener, the GPIB system performance may become unacceptableif other GPIB devices need to transfer data on the bus.Serial Poll ResponsesIf the GPIB-232CV is serial polled, its response byte will depend upon thestatus of the internal data buffers. If the serial input buffer is empty, bit oneof the status byte will be set to 1. If the serial input buffer is not empty, bitone will be set to 0. If the GPIB input buffer is empty, bit zero of the statusbyte will be set to 1. If the GPIB input buffer is not empty, bit one will beset to 0. In all cases, bit six will be set to 1 if the GPIB-232CV isrequesting service, and will be set to 0 otherwise.Listen-Only ModeThe GPIB-232CV will be located at the GPIB address specified by switches4 through 8 of the configuration DIP switch at location U22. TheGPIB-232CV also has the ability to be configured as a listen-only device ifall GPIB address switches are set to ON. In the listen-only mode, noaddressing is required to make the GPIB-232CV a GPIB Listener and itcannot be unaddressed to listen. All data transferred on the GPIB will beaccepted by the GPIB-232CV and output to the serial port (even if the data