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Chapter 5, Advanced Operations
Status Reporting
Accessing the Output Queue
When messages are sent to the Test Set, it decodes the message to determine what
commands have been sent. Depending upon the type of command, the Test Set’s
processor sends messages to various parts of the instrument. Many commands
generate data which must be sent back to the controller. This data is buffered in
the Output Queue until it is read by the controller. The availability of data is
summarized in the MAV bit of the Status Byte Register. The state of the MAV
message indicates whether or not the Output Queue is empty. The MAV message
is TRUE, logic 1, when there is data in the Output Queue and FALSE, logic 0,
when it is empty. The Output Queue is read by addressing the Test Set to TALK
and then handshaking the bytes out of the Output Queue. Depending upon the
type of command sent, the data may appear in the Output Queue almost
immediately, or it may take several seconds (as is the case with some Signaling
Decoder measurements). Care should be exercised when reading the Output
Queue since the GPIB bus will, by design, wait until the data is available before
processing further bus messages.
Reading the Output Queue
Example
Enter 714;Output_data