American Magnetics 420 Power Supply Programmer - Manual (Page 90)

72 Rev. 7
Remote Interface Reference
SCPI Status System
example, if the command *SRE 4 is sent to the Model 420, then if a
quench detect subsequently occurs, the Model 420 will immediately
generate an SRQ on the IEEE-488 bus.
Bit 2 of the Status Byte register, indicating a quench condition, remains
set until the quench condition is cleared via the front panel or by remote
command. However, an SRQ is only asserted when the quench is first
detected. 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:
‡ A *CLS command is executed.
‡ The Standard Event register is read (only bit 5 of the Status Byte
register is cleared).
‡ The indicated condition no longer exists.
The Status Byte enable register is cleared when:
‡ The *SRE 0 command is executed.
‡ 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 420 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 420, 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 420 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 420 and may not reflect the effects of the most recently executed