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© National Instruments Corp. 7-1 NI-488.2 User Manual for Windows
Chapter 7
GPIB Programming Techniques
This chapter describes techniques for using some NI-488 functions and NI-488.2 routines
in your application program.
For more detailed information about each function or routine, refer to the NI-488.2
Function Reference Manual for DOS/Windows.
Termination of Data Transfers
GPIB data transfers are terminated either when the GPIB EOI line is asserted with the
last byte of a transfer or when a preconfigured end-of-string (EOS) character is
transmitted. By default, the NI-488.2 driver asserts EOI with the last byte of writes and
the EOS modes are disabled.
You can use the ibeot function to enable or disable the end of transmission (EOT)
mode. If EOT mode is enabled, the NI-488.2 driver asserts the GPIB EOI line when the
last byte of a write is sent out on the GPIB. If it is disabled, the EOI line is not asserted
with the last byte of a write.
You can use the ibeos function to enable, disable, or configure the EOS modes. EOS
mode configuration includes the following information:
• A 7-bit or 8-bit EOS byte
• EOS comparison method–This indicates whether the EOS byte has seven or eight
significant bits. For a 7-bit EOS byte, the eighth bit of the EOS byte is ignored.
• EOS write method–If this is enabled, the NI-488.2 driver automatically asserts the
GPIB EOI line when the EOS byte is written to the GPIB. If the buffer passed into an
ibwrt call contains five occurrences of the EOS byte, the EOI line is asserted as
each of the five EOS bytes are written to the GPIB. If an ibwrt buffer does not
contain an occurrence of the EOS byte, the EOI line is not asserted (unless the EOT
mode is enabled, in which case the EOI line is asserted with the last byte of the write).
• EOS read method–If this is enabled, the NI-488.2 driver terminates ibrd, ibrda,
and ibrdf calls 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.