Status Reporting 7
Agilent InfiniiVision 5000 Series Oscilloscopes Programmer's Reference 523

Arm Event Register (AER)

This register sets bit 5 (Wait Trig bit) in the Operation Status Register and
the OPER bit (bit 7) in the Status Byte Register when the instrument
becomes armed.
The ARM event register stays set until it is cleared by reading the register
with the AER? query or using the *CLS command. If your application
needs to detect multiple triggers, the ARM event register must be cleared
after each one.
If you are using the Service Request to interrupt a program or controller
operation when the trigger bit is set, then you must clear the event
register after each time it has been set.