Lake Shore Model 475 Gaussmeter User’s Manual
6-10
Remote Operation
6.1.4.3.2 Service Request Enable Register
The Service Request Enable Register is programmed by the user and determines which summary bits of the Status Byte
may set bit 6 (RQS/MSS) to generate a Service Request. Enable bits are logically ANDed with the corresponding
summary bits, see Figure 6-5. Whenever a summary bit is set by an event register and its corresponding enable bit is set
by the user, bit 6 will set to generate a service request. The Service Request Enable command (*SRE) programs the
Service Request Enable Register and the query command (*SRE?) reads it. Reading the Service Request Enable Register
will not clear it. The register may be cleared by the user by sending *SRE 0.
Figure 6-5. Status Byte Register and Service Request Enable Register
6.1.4.3.3 Using Service Request (SRQ) and Serial Poll
When a Status Byte summary bit (or MAV bit) is enabled by the Service Request Enable Register and goes from 0 to 1,
bit 6 (RQS/MSS) of the status byte will be set. This will send a service request (SRQ) interrupt message to the bus
controller. The user program may then direct the bus controller to serial Poll the instruments on the bus to identify which
one requested service (the one with bit 6 set in its status byte).
Serial polling will automatically clear RQS of the Status Byte Register. This allows subsequent serial polls to monitor bit
6 for an SRQ occurrence generated by other event types. After a serial poll, the same event or any event that uses the
same Status Byte summary bit, will not cause another SRQ unless the event register that caused the first SRQ has been
cleared, typically by a query of the event register.
The serial poll does not clear MSS. The MSS bit stays set until all enabled Status Byte summary bits are cleared,
typically by a query of the associated event register, refer to Paragraph 6.1.4.3.4.
The programming example in Table 6-3 initiates an SRQ when a command error is detected by the instrument.
