Measurement Computing Micro 488/EX rev.2.1 - Manual (Page 187)

Section 8 IEEE 488 Primer
8.5
8.4.2 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).
8.4.3 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.
8.4.4 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.
8.4.5 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.