Measurement Computing Parallel488 - Manual (Page 37)

Section 5 IEEE 488 Primer
5.5
5.4.2 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).
5.4.3 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.
5.4.4 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.
5.4.5 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.