Agilent Technologies N1996A-503 User Reference page 334

Using The Status Monitoring Subsystem
The Status Byte Register
The Status Byte Register
The RQS bit is read and reset by a serial poll. The same bit position (MSS) is read,
non-destructively by the *STB? command. If you serial poll bit 6 it is read as RQS, but if
you send *STB it reads bit 6 as MSS. For more information refer to IEEE 488.2 standards,
section 11.
334 Chapter 6