General bus management lines:
- ATN, IFC, REN, SRQ, EOI and they are used by the Active
Controller or System Controller to manage GPIB interface
SRQ (Service Request):
- This line is used by any device from the bus.
- when is set true (low), the device notifies the Controller that it needs
servicing a request.
- Controller will perform a Serial Poll or a Parallel Poll in order to
determine which device requested a service and why.
IFC (Interface Clear):
- This line is used only by the Controller.
- When IFC line is true (low) all devices from the bus reset the GPIB
interface (Talker and Listeners are unaddressed, service request idle
and Serial Poll disabled).
REN (Remote Enable):
- This line is used only by the Controller.
- When REN line is set true (low), the bus is in remote mode, so devices
can be addressed to listen or to talk.
- A device will go into remote mode only when addressed to listen.
While in remote mode, the device ignores its local front panel controls
(only Remote / Local key is active) and it receives instructions over
GPIB interface.
- when REN line is set false (high), the bus and all devices go to local
mode.
EOI (End or Identify):
- this line is used by the active Talker
- when EOI line is true (low), the active Talker indicates that the last
byte of a data stream is sent over the interface.
- multiple termination schemes are available, depending on the GPIB
interface card you use.
ATN (Attention):
- this line is used only by the Controller
- when ATN line is true (low), the bus is in command mode. Address
and GPIB command bytes are transferred over the interface. These
bytes are used to assign Listeners and Talker, to obtain device status
etc. All devices from the bus must acknowledge them.
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