User manual

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 ser
-
vice subroutine when the SRQ is detected by the serial poll.
The serial poll automatically resets RQS of the Status Byte Register. This allows subse-
quent 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.
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 acknowl-
edge SRQ
END IF
PRINT
END
srq:
PRINT "SRQ Has Occurred--RQS (bit B6) is set (1)"
RETURN
2000-900 (J - Aug 2010) BOOK.fm Page 28 Wednesday, October 12, 2011 12:29 PM