Keithley 2000, User Manual, Page: 114 / 280

Serial poll and SRQ
Any enabled event summary bit that goes from 0 to 1 will set RQS and generate a service
request (SRQ). In your test program, you can periodically read the Status Byte Register to check
if a service request (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, service
requests (SRQs) are managed by the serial poll sequence of the Model 2000. 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 de-
tected 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 se-
rial poll, the same event can cause another SRQ, even if the event register that caused the first
SRQ has not been cleared.
A serial poll clears RQS but does not clear MSS. The MSS bit stays set until all Status Byte
event summary bits are cleared.
The following QuickBASIC 4.5 program (using the KPC-488.2 interface and the CECHP
driver) demonstrates how serial poll can be used to detect an SRQ:
CLS
OPEN "ieee" FOR OUTPUT AS #1
OPEN "ieee" FOR INPUT AS #2
PRINT #1, "output 16; *cls" 'Clear Status Byte Register
PRINT #1, "output 16; *ese 32 'Unmask command errors
PRINT #1, "output 16; *sre 32 'Unmask event summary message
PRINT #1, "output 16; *ese" 'Error - missing parameter
SLEEP 1
PRINT #1, "SPOLL 02" 'Serial poll 2000
INPUT #2, S 'Read Status Byte Register
S=S OR 191 'OR register with a mask
IF S= 255 THEN
GOSUB srq 'Go to subroutine to acknowledge
SRQ
END IF
PRINT
END
srq:
PRINT "SRQ Has Occurred--RQS (bit B6) is set (1)"
RETURN
4-28 Remote Operation