Measurement Computing Digital488 - Manual (Page 65)

Section 4 IEEE 488 Primer
4.5
4.4.2 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).
4.4.3 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.
4.4.4 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.
4.4.5 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.