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STATus Subsystem
SCPI uses four status groups - the Status Byte, the Standard Event status group, the
Operation status group, and the Questionable Data status group. The STATus
subsystem controls those command (and queries) that affect the OPERation status
group and the QUEStionable status group.
The OPERation status group provides information about the state of the monitoring
systems in an instrument. The QUEStionable data status group provides information
about the quality of instrument output and monitoring data.
Each status group consists of a condition register, transition filters, event register,
and enable register. The enable register values are stored in non-volatile memory
with the SYSTem:NVSave command and restored at power-on.
The CONDition register continuously monitors the hardware and firmware status of
the instrument. There is no latching or buffering for this register; it is updated in real
time. Condition registers are read-only.
The EVENt register latches transition events from the condition register as specified
by the transition filter. Only the positive transition filter is active in the module, this
means that a transition event will occur when a condition makes a transition from a
1
low to a high state
. Bits in the event register are latched, and once set, they remain
set until cleared by a STATus:OPERation:EVENt? query or *CLS (clear status).
There is no buffering; so while an event bit is set, subsequent events corresponding
to that bit are ignored. Event registers are read only. Events are queried in order to
determine if transitions have occurred since the last query. They do not indicate the
current state (condition) of a particular event. Nor do they indicate how many times
a transition has occurred.
The ENABle register specifies which bits in the event register can generate a
summary bit. The instrument logically ANDs corresponding bits in the event and
enable registers, and ORs all the resulting bits to obtain a summary bit. Summary bits
are, in turn, recorded in another register. The OPERation and QUEStionable status
summary bits are recorded in the Status Byte. Enable registers are read-write. Enable
registers are not affected by *CLS (Clear status). Querying enable registers does not
affect them.
Figure 3-1 shows a simplified register diagram for the status subsystem.
1.The only exception is the STATus:QUEStionable:VOLTage register which is set with the
STATus:QUESTionable:VOLTage:PTR command.
88 Programming the Enhanced Monitor
Chapter 3
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