National Instruments NI-488.2 - Manual (Page 77)

Chapter 8 NI-488.2 Programming Techniques
NI-488.2 User Manual 8-2 ni.com
enabled, in which case the EOI line is asserted with the last byte
of the write).
• EOS read method—If this is enabled, ibrd , ibrda , and ibrdf calls
are terminated when the EOS byte is detected on the GPIB, when the
GPIB EOI line is asserted, or when the specified count is reached.
If the EOS read method is disabled,
ibrd , ibrda , and ibrdf calls
terminate only when the GPIB EOI line is asserted or the specified
count has been read.
You can use the ibconfig function to configure the software to indicate
whether the GPIB EOI line was asserted when the EOS byte was read in.
Use the
IbcEndBitIsNormal option to configure the software to report
only 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 EOI
line is asserted during a read.
High-Speed Data Transfers (HS488)
National Instruments has designed a high-speed data transfer protocol for
IEEE 488 called HS488. This protocol increases performance for GPIB
reads and writes up to 8 Mbytes/s, depending on your system.
HS488 is part of the IEEE 488.1-2003 standard; thus, you can mix
IEEE 488.1, IEEE 488.2, and HS488 devices in the same system. If HS488
is enabled, HS488-compliant interfaces implement high-speed transfers
automatically when communicating with HS488 instruments. If you
attempt to enable HS488 on a GPIB interface that does not have
HS488-capable hardware, the ECAP error code is returned.
Enabling HS488
To enable HS488 for your GPIB interface, use the ibconfig function
(option IbcHSCableLength ). The value passed to ibconfig should
specify the number of meters of cable in your GPIB configuration. If you
specify a cable length that is much smaller than what you actually use,
the transferred data could become corrupted. If you specify a cable length
longer 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 for
HS488, the Controller-In-Charge must send out GPIB command bytes
(interface messages) to configure other devices for HS488 transfers.