Programmer’s Guide 1-5
Introduction to GPIB Programming
Bus Structure
Control Lines
The data bus also has five control lines that the controller uses both to
send bus commands and to address devices:
IFC Interface Clear. Only the system controller uses this
line. When this line is true (low), all devices (addressed
or not) are deselected, and go to an idle state.
ATN Attention. The active controller uses this line to define
whether the information on the data bus is a
command or is data. When this line is true (low), the
bus is in the command mode and the data lines carry
bus commands. When this line is false (high), the bus is
in the data mode and the data lines carry
device-dependent instructions or data.
SRQ Service Request. This line is set true (low) when a
device requests service: the active controller services
the requesting device. The analyzer can set the SRQ
line true (low) for a variety of reasons.
REN Remote Enable. Only the system controller uses this
line. When this line is set true (low), the bus is in the
remote mode and devices are addressed either to listen
or talk. When the bus is in remote mode and a device is
addressed, the device receives instructions from GPIB
rather than from its front panel (pressing the
softkey returns the device to front
panel operation). When this line is set false (high), the
bus and all devices return to local operation.
EOI End or Identify. This line is used by a talker to indicate
the last data byte in a multiple byte transmission, or by
an active controller to initiate a parallel poll sequence.
The analyzer recognizes the EOI line as a terminator
and it sets the EOI line true (low) with the last byte of
a message output (data, markers, plots, prints, error
messages). The analyzer does not respond to parallel
poll.
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