3152A User Manual
Racal Instruments
©
2001
SCPI and HS Command Reference 4-25
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.
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