National Instruments NI-488.2 NI-488.2 User Manual

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National Instruments NI-488.2 NI-488.2 User Manual Manual pdf 74 page image

Chapter 8 NI-488.2 Programming TechniquesNI-488.2 User Manual 8-2 ni.com• EOS read method—If this is enabled, ibrd, ibrda, and ibrdf callsare terminated when the EOS byte is detected on the GPIB, when theGPIB EOI line is asserted, or when the specified count is reached.If the EOS read method is disabled, ibrd, ibrda, and ibrdf callsterminate only when the GPIB EOI line is asserted or the specifiedcount has been read.You can use the ibconfig function to configure the software to indicatewhether the GPIB EOI line was asserted when the EOS byte was read in.Use the IbcEndBitIsNormal option to configure the software to reportonly the END bit in ibsta when the GPIB EOI line is asserted. By default,END is reported in ibsta when either the EOS byte is read in or the EOIline is asserted during a read.High-Speed Data Transfers (HS488)National Instruments has designed a high-speed data transfer protocol forIEEE 488 called HS488. This protocol increases performance for GPIBreads and writes up to 8 Mbytes/s, depending on your system.HS488 is part of the IEEE 488.1-2003 standard; thus, you can mixIEEE 488.1, IEEE 488.2, and HS488 devices in the same system. If HS488is enabled, HS488-compliant interfaces implement high-speed transfersautomatically when communicating with HS488 instruments. If youattempt to enable HS488 on a GPIB interface that does not haveHS488-capable hardware, the ECAP error code is returned.Enabling HS488To enable HS488 for your GPIB interface, use the ibconfig function(option IbcHSCableLength). The value passed to ibconfig shouldspecify the number of meters of cable in your GPIB configuration. If youspecify a cable length that is much smaller than what you actually use,the transferred data could become corrupted. If you specify a cable lengthlonger than what you actually use, the data is transferred successfully,but more slowly than if you specified the correct cable length.In addition to using ibconfig to configure your GPIB interface forHS488, the Controller-In-Charge must send out GPIB command bytes(interface messages) to configure other devices for HS488 transfers.