Status Structure; Overview - Keithley 6220 Reference Manual

11-2

Status Structure

Overview

The Model 622x provides a series of status registers and queues allowing the
operator to monitor and manipulate the various instrument events. The status
structure is shown in
byte register. This register can be read by the user's test program to determine if a
service request (SRQ) has occurred and what event caused it.
Status byte and SRQ — The status byte register receives the summary bits of
four status register sets and two queues. The register sets and queues monitor
the various instrument events. When an enabled event occurs, it sets a summary
bit in the status byte register. When a summary bit of the status byte is set and its
corresponding enable bit is set (as programmed by the user), the RQS/MSS bit
will set to indicate that an SRQ has occurred.
Status register sets — A typical status register set is made up of a condition reg-
ister, an event register, and an event enable register. A condition register is a
read-only register that constantly updates to reflect the present operating condi-
tions of the instrument.
When an event occurs, the appropriate event register bit sets to 1. The bit remains
latched to 1 until the register is reset. When an event register bit is set and its cor-
responding enable bit is set (as programmed by the user), the output (summary)
of the register will set to 1, which in turn sets the summary bit of the status byte
register.
Queues — The Model 622x uses an output queue and an error queue. The
response messages to query commands are placed in the output queue. As vari-
ous programming errors and status messages occur, they are placed in the error
queue. When a queue contains data, it sets the appropriate summary bit of the
status byte register.
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Figure 11-1. The heart of the status structure is the status
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Model 6220/6221 Reference Manual