HP 8920B, Programmer'S Manual

Page: 260 / 682

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Chapter 5, Advanced Operations
Status Reporting
Status Reporting
This section describes the status reporting structure used in the Test Set. The
structure is based on the IEEE 488.1-1987 and 488.2-1987 Standards and the
Standard Commands for Programmable Instruments (SCPI) Version 1994.0.
Status Reporting Structure Overview
Figure 3 on page 261
shows an overview of the status reporting structure used in
the Test Set. The status reporting structure is used to communicate the Test Set’s
current status information to the application program. The term status information
encompasses a variety of conditions which can occur in a Test Set, such as, has a
measurement been completed, has an internal hardware failure occurred, has a
command error occurred, has data available, and so forth. Many such conditions
can exist in the Test Set. Like conditions are grouped together and maintained in
Status Register Groups. Information in each register group is summarized into a
Summary Message Bit. Summary Message Bits always track the current status of
the associated register group. All of the Summary Message Bits are, in turn,
summarized into the Status Byte Register.
Therefore, by monitoring the bits in the Status Byte Register the application
program can determine if a condition has occurred which needs attention, which
register to interrogate to determine what condition(s) have occurred, and what
action to take in response to the condition.
NOTE: A Status Register Group Summary Message Bit may be summarized indirectly to the Status
Byte Register through a Status Register Group which is summarized directly into the Status
Byte Register.
Bits in the Status Byte Register can also be used to initiate a Service Request
message (SRQ) by enabling the associated bit in the Service Request Enable
Register. When an enabled condition exists, the Test Set sends the Service
Request message (SRQ) on the HP-IB bus and reports that it has requested service
by setting the Request Service (RQS) bit in the Status Byte Register to the TRUE,
logic 1, state. The Service Request message (SRQ) capability of the HP-IB bus is
used to automatically signal the Active Controller that the Test Set needs
attention. The application program can then interrogate the Test Set and determine
what caused it to request service. Refer to
"HP-IB Service Requests" on page 311
for information on setting up, enabling and servicing SRQ generated interrupts.