HP 8921A Programmer's Manual page 263

Example
OUTPUT 714;"*ESR?"
ENTER 714;Register_value
The *ESR? query allows the programmer to determine the current contents (bit
pattern) of the Standard Event Status Register. The Test Set responds to the
*ESR? query by placing the binary-weighted decimal value of the Standard Event
Status Register bit pattern into the Output Queue. The decimal value of the bit
pattern will be a positive integer in the range of 0 to 255. The response data is
obtained by reading the Output Queue into a numeric variable, integer or real.
Reading the Standard Event Status Register clears it (sets all bits to zero).
Example BASIC program
10 INTEGER Std_evn_stat_rg
20 OUTPUT 714;"*ESR?"
30 ENTER 714;Std_evn_stat_rg
40 PRINT Std_evn_stat_rg
50 END
Example response
32
Clearing the Event Register
The EVENT register is cleared whenever it is queried or whenever the *CLS
Common Command is sent to the Test Set.
Chapter 5, Advanced Operations
Status Reporting
263