Keysight U2722A Programmer's Reference Manual page 117

IEEE-488.2 Common Commands 13
Returned Query Format
<NR1>
The query command reads the enable register and returns a decimal value that
corresponds to the binary-weighted sum of all bits set in the register.
For example, if bit 3 (decimal value = 8) and bit 7 (decimal value = 128) are
enabled, the query command will return "+136".
Example
The following query returns the bits enabled in the register.
*ESR?
Typical Response: +16
See Also
*ESE/*ESE?
Keysight U2722A/U2723A Programmer's Reference 117