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Queues
The Model 2000 uses two queues, which are first-in, first-out (FIFO) registers:
• Output Queue - used to hold reading and response messages
• Error Queue - used to hold error and status messages
The Model 2000 Multimeter status model (Figure 4-5) shows how the two queues are struc-
tured with the other registers.
Output queue
The output queue holds data that pertains to the normal operation of the instrument. For ex-
ample, when a query command is sent, the response message is placed on the Output Queue.
When data is placed in the Output Queue, the Message Available (MAV) bit in the Status Byte
Register sets. A data message is cleared from the Output Queue when it is read. The Output
Queue is considered cleared when it is empty. An empty Output Queue clears the MAV bit in
the Status Byte Register.
Read a message from the Output Queue by addressing the Model 2000 multimeter to talk af-
ter the appropriate query is sent.
Error queue
The Error Queue holds error and status messages. When an error or status event occurs, a
message that defines the error/status is placed in the Error Queue. This queue will hold up to 10
messages.
When a message is placed in the Error Queue, the Error Available (EAV) bit in the Status Byte
Register is set. An error message is cleared from the Error/Status Queue when it is read. The Er-
ror Queue is considered cleared when it is empty. An empty Error Queue clears the EAV bit in
the Status Byte Register. Read an error message from the Error Queue by sending either of the
following SCPI query commands and then addressing the Model 2000 to talk:
• :SYSTem:ERRor?
• :STATus:QUEue
See Section 5 for complete information about reading error messages.
4-24 Remote Operation