User manual

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
structured with the other registers.
Output queue
The output queue holds data that pertains to the normal operation of the instrument. For
example, 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
after 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 Error 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.
2000-900 (J - Aug 2010) BOOK.fm Page 24 Wednesday, October 12, 2011 12:29 PM