Model 6517A Getting Started Manual Remote Operation 3-23
Generating SRQ on buffer full
When your program must wait until the Model 6517A has completed an operation, it is
more efficient to program the Model 6517A to assert the IEEE-488 SRQ line when it is
finished, rather than repeatedly serial polling the instrument. An IEEE-488 controller will
typically address the instrument to talk, then unaddress it, each time it performs a serial
poll. Repeated polling of the Model 6517A will generally reduce its overall reading
throughput. Therefore, use the srq%() function call.
The Model 6517A provides a status bit for nearly every operation it performs. It can be
programmed to assert the IEEE-488 SRQ line whenever a status bit becomes true or false.
The IEEE-488 controller (your computer) can examine the state of the SRQ line without
performing a serial poll, thereby detecting when the 6517A has completed its task without
interrupting it in the process.
The following example program segment sets up the Model 6517A to assert SRQ when
the reading buffer has completely filled, then arms the reading buffer, initiates readings,
and waits for the Model 6517A to indicate that the buffer is full.
This is not a complete program. Not shown are the commands to configure the trigger
model and the reading buffer (see the next example). The example shown here can be
modified for any event in the Model 6517A status reporting system.
'Reset STATus subsystem (not affected by *RST)
CALL SEND(27, "stat:pres;*cls", status%)
CALL SEND(27, "stat:meas:enab 512", status%) 'enable BFL
CALL SEND(27, "*sre 1", status%) 'enable MSB
CALL SEND(27, "trac:feed:cont next", status%)
' Start everything
CALL SEND(27, "init", status%)
WaitSRQ:
IF (NOT(srq%)) THEN GOTO WaitSRQ
CALL SPOLL(27, poll%, status%)
IF (poll% AND 64)=0 THEN GOTO WaitSRQ
Notice that after the program has detected an asserted SRQ line, it serial polls the
Model 6517A to determine if it is the device requesting service. This is necessary for two
reasons:
• Serial polling the Model 6517A causes it to quit asserting the SRQ line.
• In test systems that have more than one IEEE-488 instrument programmed to assert
SRQ, your program must determine which instrument is actually requesting
service.
Once an event register has caused a service request, it cannot cause another service request
until you clear it by reading it (in this case using STATus:MEASurement[:EVENt]?)
or by sending the *CLS command.
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