Appendix B: Status model
Model 2110 5½ Digit Multimeter Reference Manual
B-4
2110-901-01 Rev. C/August 2013
Status byte and service request (SRQ)
Service request is controlled by two 8-bit registers: The Status Byte Register and the Status Byte
Enable Register.
Status Byte Register
The summary messages from the status registers and queues are used to set or clear the appropriate
bits (B2, B3, B4, and B5) of the Status Byte Register. These summary bits do not latch, and their
states (0 or 1) are solely dependent on the summary messages (0 or 1). For example, if the Standard
Event Register is read, its register will clear. As a result, its summary message will reset to 0, which
will then reset the ESB bit in the Status Byte Register.
The bit definitions of the Status Byte Register are described in the following table.
Status Byte Register
Bit
Definition
Decimal
value
Description
0
Not used
1
Set to 0.
1
Not used
2
Set to 0.
2
Error Available (EAV)
4
Set bit indicates that a measurement event has
occurred.
3
Questionable
Summary Bit (QSB)
8
One or more bits are set in the Questionable Data Register
indicating that an enabled questionable event has occurred
(bits have to be “enabled” in the enable register).
4
Message Available
(MAV)
16
Set summary bit indicates that a response message is
present in the Output Buffer.
5
Event Summary Bit
(ESB)
32
One or more bits are set in the Standard Event Register,
indicating that an enabled standard event has occurred (bits
have to be “enabled” in the enable register).
6
Request Service
(RQS)
64
Set bit indicates that an enabled summary bit of the Status
Byte Register is set and the instrument requires service
(Serial Poll).
7
Not used
128
Set to 0.
Using the Message Available Bit (MAV)
The Output Buffer holds response messages. Response messages are the messages sent in
response to query commands. When a response message is placed in the Output Buffer, the
Message Available Bit (MAV) (B4) in the Status Byte Register sets. A data message is cleared from
the Output Buffer when it is read. The Output Buffer is considered cleared when it is empty. An empty
Output Buffer clears the MAV bit in the Status Byte Register. A message is read from the Output
Buffer by addressing the instrument to talk after the appropriate query is sent.
Use the READ? command to initiate measurements after the trigger conditions are met.
Use the INITiate command to store readings in the instrument's internal memory.
Use the FETCH? command to transfer readings to the instrument's Output Buffer.
When the instrument takes the first reading in response to a READ? command, the MAV bit is set
indicating that a message is in the Output Buffer.
