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Chapter 4 Remote Interface Reference
The SCPI Status Registers
102
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 groups. The status
byte register records high-level summary information reported in the other register
groups. The diagram on the subsequent pages illustrates the SCPI status system used
by the power supply.
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 two-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.