Measurement Computing Micro 488/EX rev.2.1 - Manual (Page 180)

Section 7 Peripheral Pass-Thru Operation
7.8
7.6.3 Device Clear (DCL and SDC)
Device Clear resets the Micro488/EX's IEEE input and serial input
buffers. Any pending data and Service Requests (SRQ), including the
information they convey, are lost. In addition, the XON serial control
character is transmitted if XON/XOFF is enabled.
7.6.4 Interface Clear (IFC)
IFC places the Micro488/EX in the Talker/Listener Idle State. It
clears any pending requests for service (SRQ). The condition which
caused the SRQ remains unmodified.
7.6.5 Serial Poll Enable (SPE)
When Serial Poll Enabled, the Micro488/EX sets itself to respond to a
serial poll with its serial poll status byte if addressed to talk. When the
serial poll byte is accepted by the controller, any pending SRQs are cleared.
The Micro488/EX will continue to try to output its serial poll response
until it is 'Serial Poll Disabled' by the controller.
7.6.6 Serial Poll Disable (SPD)
Disables the Micro488/EX from responding to serial polls by the
controller.
7.6.7 Unlisten (UNL)
UNL places the Micro488/EX in the Listener Idle State.
7.6.8 Untalk (UNT)
UNT places the Micro488/EX in the Talker Idle State.