Lake Shore 625, User Manual, Page: 67 / 132

Lake Shore Model 625 Superconducting MPS User’s Manual
Computer Interface Operation 5-13
Figure 5-7. Status Byte Register and Service Request Enable Register
5.1.4.4.3 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 5.1.4.4.4.
The programming example in Table 5-3 initiates an SRQ when a command error is detected by the instrument.
Table 5-3. Programming Example to Generate an SRQ
Command or Operation Description
*ESR? Read and clear the Standard Event Status Register.
*ESE 32 Enable the Command Error (CME) bit in the Standard Event Status Register
*SRE 32 Enable the Event Summary Bit (ESB) to set the RQS
*ABC Send improper command to instrument to generate a command error
Monitor bus Monitor the bus until the Service Request interrupt (SRQ) is sent.
Initiate Serial Poll
Serial Poll the bus to determine which instrument sent the interrupt and clear the
RQS bit in the Status Byte.
*ESR?
Read and clear the Standard Event Status Register allowing an SRQ to be
generated on another command error.