HP 8509A Programming Manual page 18

Handshake Lines
Control Lines
IFC
Interface Clear. Only the system controller uses this line. When this line is true
(low) all devices (addressed or not) unaddress and go to an idle state.
ATN
Attention. The active controller uses this line to de ne whether the information
on the data bus is a
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.
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 and a device is addressed, it receives
instructions from HP-IB rather than from its front panel. 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 pulls the
EOI line with the last byte of a message output (data, markers, plots, prints,
error messages).
3-2 HP-IB Overview
command data
or is . When this line is true (low) the bus is