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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

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.

Chapter 4 Remote Interface Reference

The SCPI Status Model

159

Agilent Technologies 34420A User Manual

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