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to select the low-level IEEE-488 SRQ signal set by summary bits. As the
status byte bit 6 is set, an IEEE-488 SRQ interrupt message will be sent
automatically to the bus controller which may poll the instruments on the
bus to identify which one requested service. To read the status byte
which is using an IEEE-488 serial poll or to read the event register,
whose summary bit is cauing the service request, will clear the request
service.
You send the IEEE-488 serial poll message to read the status byte
summary register. And to query the summary register will return a
decimal value corresponding to the binary-weighted sum of the bits set
in the register. And serial poll will clear the “request service bit”
automatically in the status byte summary register, but no other bits are
affected, i.e. to perform a serial poll won’t affect instrument throughput.
※
Note: The synchronization between the bus controller program and
the instrument isn’t able to be ensured by the IEEE-488.2 standard. So
users can apply the *OPC? command to ensure that commands sent to
the instrument previously have completed. And to execute a serial poll
before applying *RST, *CLS or other commands have completed can let
pervious conditions be reported.
Read the Status Byte by using *STB?
The *STB? command (status byte query) is like a serial poll except it acts
similar to any other instrument command. This command returns the
same result as an IEEE-488 serial poll except that the “request service bit
6” isn’t cleared if a serial poll has occurred. And the IEEE-488 bus
interface hardware can’t automatically handle the *STB? command. It
will work only after previous commands have completed, and it’s
impossible to poll by using the *STB? command. Moreover, to use this
command doesn’t clear the status byte summary register.
Procedures of Interrupting the Bus Controller by Using SRQ
1.
Send a bus device clear message.
2.
Clear the event register by using the *CLS command.
3.
Set the *ESE and *SRE commands to enable masks.
4.
Send the *OPC? command and enter the result to enable
