F.W. Bell 7030, Instruction Manual

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F.W. BELL Model 7030 Gauss/Tesla Meter Instruction Manual
Section 7 – Remote Operation 7-9
STATUS BYTE
AND
SERVICE
REQUEST (SRQ) The IEEE-488 bus is a common bus linking a master controller (your
computer) to one or more instruments. If an instrument requires action from
the controller it must somehow get the controller’s attention. A hardware line
on the bus called SRQ (service request) is used to signal the controller that
one or more instruments on the bus require attention. A bit in the STATUS
BYTE called RQS (request for service) also sets. The master then reads the
STATUS BYTE from each instrument to determine which instrument(s)
require service.
On the RS-232 port there is no hardware method of signaling a service
request, so the STATUS BYTE must be inspected (“polled”) to determine if
service is required.
The RQS bit can set if any of the summary bits from the MEASUREMENT
EVENT, OPERATION EVENT, STANDARD EVENT or QUESTIONABLE
EVENT registers are set, or if an error or output message is ready to be
transmitted to the master. The SRQ ENABLE register is a mask register that
is used to allow any of these conditions to set the RQS bit, and thus the SRQ
line. Setting any bit in the SRQ ENABLE register to “1” will allow a
corresponding “1” in the STATUS BYTE register to set the RQS bit.
These registers are depicted in
Figure 7-4 . An example of their usage
appears at the end of this section.
Figure 7-4 Status Byte and SRQ
Enable registers