Model 6485 Picoammeter Instruction Manual Status Structure 10-9
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 command. 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 pro-
gram and read the SRQ enable register are listed in Table 10-6.
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 exam-
ple, branch to an appropriate subroutine that will service the request.
Typically, SRQs are managed by the serial poll sequence of Model 6485. If an SRQ does
not occur, bit B6 (RQS) of the status byte register will remain cleared, and the program
will simply 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 Model 6485. 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.
Status byte and service request commands
The commands to program and read the status byte register and service request enable reg-
ister are listed in Table 10-3. For details on programming and reading registers, see “Pro-
gramming enable registers,” page 10-5, and “Reading registers,” page 10-6.
To reset the bits of the service request enable register to 0, use 0 as the parameter value for
the *SRE command (i.e. *SRE 0).
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