You can set or clear the individual bits of the Service Request Enable Register by using the *SRE
common command or status.request_enable. To read the Service Request Enable Register,
use the *SRE? query or print(status.request_enable). The Service Request Enable Register
clears when power is cycled or a parameter value of 0 is sent with a status request enable command
(for example, a *SRE 0 or status.request_enable = 0 is sent). The commands to program and
read the SRQ Enable Register are listed in Status byte and service request commands (on
page 12-19).
Serial polling and SRQ
Any enabled event summary bit that goes from 0 to 1 sets bit B6 and generates a service request
(SRQ).
In your test program, you can periodically read the Status Byte to check if an SRQ occurred and what
caused it. If an SRQ occurred, the program can, for example, branch to an appropriate subroutine
that services the request.
SRQs can be managed by the serial poll sequence of the instrument. If an SRQ does not occur, bit
B6 (RQS) of the Status Byte Register remains cleared, and the program proceeds normally after the
serial poll is performed. If an SRQ does occur, bit B6 of the Status Byte Register is set, and the
program can branch to a service subroutine when the SRQ is detected by the serial poll.
The serial poll automatically resets RQS of the Status Byte Register. This allows subsequent serial
polls to monitor bit B6 for an SRQ occurrence that is generated by other event types.
The serial poll does not clear the low-level registers that caused the SRQ to occur. You must clear the
low-level registers explicitly. Refer to Clearing registers (on page 12-14).
For common commands and TSP commands, B6 is the MSS (Message Summary Status) bit. The
serial poll does not clear the MSS bit. The MSS bit remains set until all enabled Status Byte Register
summary bits are reset.
SPE, SPD (serial polling)
For the GPIB interface only, the SPE and SPD general bus commands are used to serial poll the
System SourceMeter
®
instrument. Serial polling obtains the serial poll byte (status byte). Typically,
serial polling is used by the controller to determine which of several instruments has requested
service with the SRQ line.
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