Measurement Computing Digital HS - Manual (Page 44)

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.