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The SCPI Status Model
All
SCPI
instruments implement status registers in the same way. The
status system records various instrument conditions in four register
groups: the Status Byte register, the Standard Event register, The
Operational Status register, and the Questionable Data register. The
status byte register records high-level summary information reported in
the other register groups. The diagram on the next page illustrates the
SCPI
status system used by the meter.
Chapter 6, “Application Programs,” contains example programs showing
the use of the status registers. You may find it useful to refer to the
programs after reading the following section in this chapter.
What is an Event Register?
The standard event and questionable data registers have event registers .
An event register is a read-only register that reports defined conditions
within the meter. Bits in the event registers
are latched. Once an event
bit is set, subsequent state changes are ignored. Bits in an event register
are automatically cleared by a query of that register (such as
*ESR?
or
STAT:QUES:EVEN?
) or by sending the
*CLS
(clear status) command. A
reset (
*RST
) or device clear will not clear bits in event registers. Querying
an event register returns a decimal value which corresponds to the
binary-weighted sum of all bits set in the register.
What is an Enable Register?
An enable register defines which bits in the corresponding event register
are logically ORed together to form a single summary bit. Enable
registers are both readable and writable. Querying an enable register
will not clear it. The
*CLS
(clear status) command does not clear enable
registers but it does clear the bits in the event registers. The
STATus:PRESet
command will clear the questionable data enable
register. To enable bits in an enable register, you must write a decimal
value which corresponds to the binary-weighted sum of the bits you wish
to enable in the register.
What is a Condition Register?
A condition register actively indicates the current state of the instrument.
Bits in the condition register are not latched, and change as the
conditions within the instrument change. The event register latches the
changes in the condition register bits.
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Chapter 4 Remote Interface Reference
The SCPI Status Model
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