Fluke PM6685 Outdoor Timer User Manual


 
State Purpose
IDLE Wait for messages
READ Read and execute mes
-
sages
QUERY Store responses to be
sent
SEND Send responses
RE
-
SPONSE
Complete sending re
-
sponses
DONE Finished sending re
-
sponses
DEADLOCK The device cannot buffer
more data
Action, Reason
Untermin-
ated,
The controller attempts to
read the device without
first having sent a com-
plete query message
Interrupted, The device is interrupted
by a new program mes-
sage before it finishes
sending a response mes-
sage
Protocol Requirements
In addition to the above functional ele
-
ments, which process the data, the mes
-
sage exchange protocol has the following
characteristics:
The controller must end a program mes
-
sage containing a query with a message
terminator before reading the response
from the device (address the device as
talker). If the controller breaks this rule,
the device will report a query error
(unterminated action).
The controller must read the response to a
query in a previously (terminated) program
message before sending a new program
message. When the controller violates this
rule, the device will report a query error
(interrupted action).
The instrument sends only one response
message for each query message. If the
query message resulted in more than one
answer, all answers will be sent in one re
-
sponse message.
n
Order of Execution
Deferred Commands
Execution control collects commands un
-
til the end of the message, or until it finds
a query or other special command that
forces execution. It then checks that the
setting resulting from the commands is a
valid one: No range limits are exceeded,
no coupled parameters are in conflict, etc.
If this is the case, the commands are exe-
cuted in the sequence they have been re-
ceived; otherwise, an execution error is
generated, and the commands are dis-
carded.
This deferred execution guarantees the
following:
All valid commands received before a
query are executed before the query is exe
-
cuted.
All queries are executed in the order they
are received.
The order of execution of commands is never
reversed.
n
Sequential and Overlapped
Commands
There are two classes of commands: se
-
quential and overlapped commands. All
commands in the CNT-8X counters are
sequential, that is one command finishes
before the next command executes.
Introduction to SCPI
How does SCPI Work in the Instrument? 3-5