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Chapter 4 Remote Interface Reference
The SCPI Status Registers
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The SCPI Status Registers
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 Status
register group. The status byte register records high-level summary
information reported in the other register groups. The diagrams on the
subsequent pages illustrate the SCPI status system used by the power supply.
An example program is included in chapter 6, “Application Programs,”
which shows 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?
An
event register
is a read-only register that reports defined conditions
within the power supply. Bits in an event register
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. 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
Multiple
Logical Output?
The three-logical outputs of the power supply include an INSTrument
summary status register and an individual instrument ISUMmary register for
each logical output. The ISUMmary registers report to the INSTrument
register, which in turn reports to bit 13 of the Questionable status register.
This is shown pictorially on the next page.