User`s manual

CHAPTER 9 BUS TUTORIAL 73
9.9. Other Bus Lines
The three remaining bus lines are:
1) REN (Remote Enable) The system controller sets REN low and then addresses the
devices to listen before they will operate under remote control.
2) IFC (Interface Clear) Only the system controller can activate this line. When IFC is
set true, all talkers, listeners and active controllers go to their inactive states.
3) EOI (End or Identify) This line is used to indicate the end of a multiple byte
transfer sequence or, in conjunction with ATN, to execute a parallel poll sequence.
9.10. Bus Operating Considerations
When a device is powered on during system operation, it may activate IFC and cause
the active controller on the bus to halt with an error. The controller must send IFC to
regain active control.
Prior to addressing new listeners it is recommended that all previous listeners be
unaddressed using the UNL command (?).
only one talker can be addressed at a time. When a new talker is addressed the former
talker is automatically unaddressed.
The maximum cumulative length of the IEEE-488 bus cable in any system must not
exceed more than 2 meters of cable per device or 20 meters, whichever is less, unless
bus Expanders or Extenders are used.
For more information about the IEEE-488 bus, please refer to the IEEE reference
document.