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
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the instrument isn’t able to be ensured by the IEEE-488.2 standard. So
you 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
Send a bus device clear message.
Clear the event register by using the *CLS command.
Set the *ESE and *SRE commands to enable masks.
Send the *OPC? command and enter the result to enable
synchronization.
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