Remote Control
R&S
®
CMW500
178User Manual 1173.9463.02 ─ 06
5.6.4.2 Serial Poll
In a serial poll, the controller queries the STatus Bytes of the devices in the bus system
one after another. The query is made via interface messages, so it is faster than a poll
by means of *STB?.
The serial poll method is defined in IEEE 488.1 and used to be the only standard possi-
bility for different instruments to poll the status byte. The method also works for instru-
ments which do not adhere to SCPI or IEEE 488.2.
The serial poll is mainly used to obtain a fast overview of the state of several instruments
connected to the controller.
5.6.4.3 Parallel Poll
In a parallel poll, up to eight instruments are simultaneously requested by the controller
by means of a single command to transmit 1 bit of information each on the data lines,
i.e., to set the data line allocated to each instrument to a logical "0" or "1".
In addition to the SRE register, which determines the conditions under which an SRQ is
generated, there is a Parallel Poll Enable register (PPE). This register is ANDed with the
STB bit by bit, considering bit 6 as well. The results are ORed, the result is possibly
inverted and then sent as a response to the parallel poll of the controller. The result can
also be queried without parallel poll by means of the command "*IST?".
The parallel poll method is mainly used to find out quickly which one of the instruments
connected to the controller has sent a service request. To this effect, SRE and PPE must
be set to the same value.
5.6.4.4 Query of an Instrument Status
Each part of any status register can be read by means of queries. There are two types
of commands:
● The Common Commands *ESR?, *IDN?, *IST?, *STB? query the higher-level
registers.
●
The commands of the STATus system query the SCPI registers (e.g.
STATus:OPERation...)
All queries return a decimal number which represents the bit pattern of the status register.
This number is evaluated by the controller program.
Queries are usually used after an SRQ in order to obtain more detailed information on
the cause of the SRQ.
Decimal representation of a bit pattern
The STB and ESR registers contain 8 bits, the SCPI registers 16 bits. The contents of a
status register is keyed and transferred as a single decimal number. To make this pos-
sible, each bit is assigned a weighted value. The decimal number is calculated as the
sum of the weighted values of all bits in the register that are set to 1.
Status Reporting System
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