The Status Byte Register (Stb); Reading The Status Byte Register - Racal Instruments 3151 User Manual

The Status Byte
Register (STB)
Reading the Status
Byte Register
SCPI Command Reference 4-18
The Status Byte summary register contains conditions from the other
registers. Query data waiting in the generator's output buffer is
immediately reported through the Message Available bit (bit 4). Bits
in the summary register are not latched. Clearing an event register
will clear the corresponding bits in the Status Byte summary register.
Description of the various bits within the Status Byte summary
register is given in the following:
Bit 0 - Decimal value 1. Not used, always set to 0.
Bit 1 - Decimal value 2. Not used, always set to 0.
Bit 2 - Decimal value 4. Not used, always set to 0.
Bit 3 - Decimal value 8. Not used, always set to 0.
Bit 4 - Decimal value 16. Message Available Queue Summary
Message (MAV). The state of this bit indicates whether or not the
output queue is empty. The MAV summary message is true when the
output queue is not empty. This message is used to synchronize
information exchange with the controller. The controller can, for
example, send a query command to the device and then wait for
MAV to become true. If an application program begins a read
operation of the output queue without first checking for MAV, all
system bus activity is held up until the device responds.
Bit 5 - Decimal value 32. Standard Event Status Bit (ESB) Summary
Message. This bit indicates whether or not one or more of the
enabled ESB events have occurred since the last reading or clearing
of the Standard Event Status Register.
Bit 6 - Decimal value 64. Master Summary Status (MSS)/Request
Service (RQS) Bit. This bit indicates if the device has at least one
condition to request service. The MSS bit is not part of the IEEE-
STD-488.1 status byte and will not be sent in response to a serial
poll. However, the RQS bit, if set, will be sent in response to a serial
poll.
Bit 7 - Decimal value 128. Not used, always set to 0.
The Status Byte summary register can be read with the *STB?
common query. The *STB? common query causes the generator to
send the contents of the Status Byte register and the MSS (Master
Summary Status) summary message as a single <NR1 Numeric
Response Message> element. The response represents the sum of
the binary-weighted values of the Status Byte Register. The *STB?
common query does not alter the status byte.
3151 And 3151A User Manual