The SCPI Status Model
All SCPI instruments implement status registers in the same way.
The status system records various instrument conditions in three
register groups: the Status Byte register, the Standard Event 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.
Chapter 6, “Application Programs,” contains an example program
showing the use of the status registers. You may find it useful to refer
to the program 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 multimeter. 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.
Chapter 4 Remote Interface Reference
The SCPI Status Model
134
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