American Magnetics 187 Self-Compensating Liquid Level Controller - Manual (Page 44)

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Remote Interface Reference
SCPI Status System
Bit 1 of the Status Byte register, indicating that the controller output is
energized, remains set until the controller output is de-energized via the
front panel, a fill timeout, or by remote command. However, an SRQ is
only asserted when the controller output transitions from de-energized to
energized. Bits 3 and 4, indicating available data in an output buffer, are
similar in that the SRQ is only asserted when data is first available in an
output buffer. Bits 3 and 4 remain set until all data has been read from the
respective output buffer.
The Status Byte condition register is cleared when:
W A *CLS command is executed.
W The Standard Event register is read (only bit 5 of the Status Byte
register is cleared).
W The indicated condition no longer exists.
The Status Byte enable register is cleared when:
W The *SRE 0 command is executed.
W The power is turned off and then back on, and the instrument was
configured for
*PSC 1 (power-on status clear). The enable register
setting is persistent if the Model 187 is configured for *PSC 0 (no
status clear on power-on).
4.2.2.2 Serial Polling and the Service Request (SRQ)
In order to use the SRQ feature of the Model 187, you must configure your
host computer and IEEE-488 interface card to respond to the IEEE-488
service request. If the Status Byte enable register enables any bits of the
Status Byte register, then the enabled bit(s) will generate an SRQ when
they transition from “0” to “1”. The host computer can then poll the
instruments on the IEEE-488 bus to determine which is asserting the
service request line (the instrument which returns a response to a Serial
Poll with bit 6 set).
Note
If the Model 187 receives a Serial Poll, bit 6 of the Status Byte
register is cleared and the service request line (SRQ) is cleared.
If more than one bit is enabled in the Status Byte enable register, then the
user must query the Status Byte register by issuing either a Serial Poll
message, or the
*STB? command. A Serial Poll is executed immediately by
the Model 187 and may not reflect the effects of the most recently executed
command. Use the
*OPC? command for positive indication that all prior
commands have been executed.