SCPI Command Reference 4-18
The Status Byte Register
(STB)
The Status Byte summary register contains conditions from the
other registers. Query data waiting in the synthesizer'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.
Reading the Status Byte
Register
The Status Byte summary register can be read with the *STB?
common query. The *STB? common query causes the synthesizer
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.
Clearing the Status Byte
Register
The entire Status Byte register can be cleared by removing the
reasons for service from Auxiliary Status registers. Sending the
*CLS command to the device after a SCPI command terminator and
before a Query clears the Standard Event Status Register and
clears the output queue of any unread messages. With the output
queue empty, the MAV summary message is set to FALSE.
Methods of clearing other auxiliary status registers are discussed in
the following paragraphs.
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