Measurement Computing Micro 488/EX rev.2.1 - Manual (Page 191)

Section 8 IEEE 488 Primer
8.9
8.7.8 Selected Device Clear (SDC)
This causes a single device to be initialized to a pre-defined or power up
state. (&H04)
8.7.9 Serial Poll Disable (SPD)
The SPD command disables all devices from sending their Serial Poll
status byte. (&H19)
8.7.10 Serial Poll Enable (SPE)
A device which is Addressed to Talk will output its Serial Poll status
byte after SPE is sent and ATN is unasserted. (&H18)
8.7.11 Group Execute Trigger (GET)
This command usually signals a group of devices to begin executing a
triggered action. This allows actions of different devices to begin
simultaneously. (&H08)
8.7.12 Take Control (TCT)
This command passes bus control responsibilities from the current
Controller to another device which has the ability to control. (&H09)
8.7.13 Secondary Command Group (SCG)
These are any one of the 32 possible commands (0 to 31) in this group.
They must immediately follow a talk or listen address. (&H60 to &H7F)