Sony Tektronix VX4792 - Page 185

Status and Event Reporting
4-6
VX4792 User Manual
The Event Queue is a FIFO (First In, First Out) queue which can hold up to 20
instrument-generated events. When the number of events exceeds 20, the 20
th
event is replaced by event code 350, “Queue overflow”.
To read out the contents from the Event Queue, perform the following steps:
1. Send  — to read out the contents of SESR. When the contents
of SESR are read out, SESR is cleared allowing you to take out events
from the Event Queue.
2. Send one of the following queries:
H  — to read out and return all events made available by .
The  query returns both the event code and message text.
H  — to read out and return the oldest event of those made
available by . The  query returns only the event code.
H  — to read out and return the oldest event of those made
available by . The  query returns both the event code and
message text.
Reading the SESR erases any events that were made available by previous 
reads, unless they were not read from the Event Queue. Events that occur after an
 read are put in the Event Queue but are not available until  is used
again.
Processing Sequence
Figure 4–6 shows the status and event processing that is summarized below.
1. An event occurs which causes the DESR to be checked. Based on the state of
the DESR, the following actions occur:
H If the control bit for that event is set in the DESER, then the SESR bit
that corresponds to this event is set to 1.
H The set control bit allows the event to be placed into the Event Queue.
Placing the event in the Event Queue sets the MAV bit in the SBR to 1.
H If the control bit for that event is also set in the ESER, then the ESB bit
of SBR is also set to 1.
2. When either bit of SBR has been set to 1 and the corresponding control bit
of SRER is also set, then the MSS bit of SBR is set and a service request
is generated for use with GPIB interface operation.
Event Queue