User manual

Remote Control
R&S
®
RTO
415User Manual 1316.0827.02 ─ 06
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Query of a specific instrument status by means of commands
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Query of the error queue
Service Request
Under certain circumstances, the instrument can send a service request (SRQ) to the
controller. Usually this service request initiates an interrupt at the controller, to which the
control program can react appropriately. As evident from figure 16-2, an SRQ is always
initiated if one or several of bits 2, 3, 4, 5 or 7 of the status byte are set and enabled in
the SRE. Each of these bits combines the information of a further register, the error queue
or the output buffer. The ENABle parts of the status registers can be set such that arbitrary
bits in an arbitrary status register initiate an SRQ. In order to make use of the possibilities
of the service request effectively, all bits should be set to "1" in enable registers SRE and
ESE.
The SRQ is the only possibility for the instrument to become active on its own. Each
controller program should cause the instrument to initiate a service request if errors occur.
The program should react appropriately to the service request.
Serial Poll
In a serial poll, just as with command *STB, the status byte of an instrument is queried.
However, the query is realized via interface messages and is thus clearly faster.
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.
Parallel Poll
In a parallel poll, up to eight instruments are simultaneously requested by the controller
using 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) which is ANDed with the STB
bit by bit, considering bit 6 as well. This register is ANDed with the STB bit by bit, con-
sidering 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 using the command *IST.
The instrument first has to be set for the parallel poll using the command PPC. This com-
mand allocates a data line to the instrument and determines whether the response is to
be inverted. The parallel poll itself is executed using PPE.
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.
Basics