7-8 Status Structure
The individual bits of the service request enable register can be set or cleared by using the
*SRE common command. To read the service request enable register, use the *SRE? query com-
mand. The service request enable register clears when power is cycled or a parameter value of 0
is sent with the *SRE command (i.e. *SRE 0). The commands to program and read the SRQ
enable register are listed in Table 7-2.
Serial polling and SRQ
Any enabled event summary bit that goes from 0 to 1 will set bit B6 and generate an SRQ
(service request). In your test program, you can periodically read the status byte to check if an
SRQ has occurred and what caused it. If an SRQ occurs, the program can, for example, branch
to an appropriate subroutine that will service the request.
Typically, SRQs are managed by the serial poll sequence of the power supply. If an SRQ does
not occur, bit B6 (RQS) of the status byte register will remain cleared, and the program will sim-
ply proceed normally after the serial poll is performed. If an SRQ does occur, bit B6 of the status
byte register will 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 generated by other event types. After a
serial poll, the same event can cause another SRQ, even if the event register that caused the first
SRQ has not been cleared.
The serial poll does not clear MSS. The MSS bit stays set until all status byte summary bits
are reset.
SPE, SPD (serial polling)
The SPE, SPD general bus command is used to serial poll the power supply. 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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