User`s manual

Chapter 6 121
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 6-1 on page 122 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 167 for information on setting up, enabling
and servicing SRQ generated interrupts.