Measurement Computing Isolator488 - Manual (Page 26)

Section 3 IEEE 488 Primer
3-5
3.4.2 Interface Clear (IFC)
The IFC line is used only by the System Controller. It is used to
place all bus devices in a known state. Although device configurations
vary, the IFC command usually places the devices in the Talk and
Listen Idle states (neither Active Talker nor Active Listener).
3.4.3 Remote Enable (REN)
When the System Controller sends the REN command, bus
devices will respond to remote operation. Generally, the REN command
should be issued before any bus programming is attempted. Only the
System Controller has control of the Remote Enable line.
3.4.4 End or Identify (EOI)
The EOI line is used to signal the last byte of a multibyte data
transfer. The device that is sending the data asserts EOI during the
transfer of the last data byte. The EOI signal is not always necessary as
the end of the data may be indicated by some special character such as
carriage return.
The Active Controller also uses EOI to perform a Parallel Poll by
simultaneously asserting EOI and ATN.
3.4.5 Service Request (SRQ)
When a device desires the immediate attention of the Active
Controller it asserts SRQ. It is then the Controller's responsibility to
determine which device requested service. This is accomplished with a
Serial Poll or a Parallel Poll.