Fluke 8845A - Output Data

Remote Operation
FLUKE 8842A Emulation Mode
89
• RULE 3: Read the output data generated by one input command string before
sending the next input command string.
Output data remains available in the output buffer until it is read, or until the
next input command string is received. As soon as the controller finishes reading the
output buffer, or as soon as the Meter receives a new input terminator, the Data
Available bit in the serial poll register is set false. When this bit is false, data can no
longer be read from the output buffer. Therefore, an output string which is available
must be read by the controller before, rather than after, the next input command
string is sent.
Rule 3 is most evident in the external trigger mode, and is best demonstrated by a
programming example. The following program is written first incorrectly, and then
correctly, in Fluke BASIC using the 1722A Instrument Controller.
Incorrect Example
100 PRINT @3, "T1 ? "
200 PRINT @3, "F4"
300 INPUT @3, A
In this incorrect example, the INPUT statement is located incorrectly for reading the
measurement data from line 100. The new input command string "F4" disallows the
reading of data from the output buffer.
Correct example
100 PRINT @3, "T1 ? "
200 INPUT @3, A
300 PRINT @3, "F4"
• RULE 4: If an input command string contains a trigger, enter the commands in the
following order:
a. Commands to configure the instrument (if any).
b. The trigger command.
c. Commands to re-configure the instrument (if any).
d. Terminator(s).
The principle behind this rule is that the 8842A executes all commands in the exact
order they are received, from left to right as written.
Example Explanation
“F3 F4 ?” Improper construction. F3 is effectively discarded.
“F3 ? F4” Correct construction. The Meter is configured in F3,
and the trigger is executed. Then the Meter is left in F4.
Output Data
The following paragraphs describe the data that can be loaded into the output buffer of
the Meter and sent to the IEEE-488 bus. The paragraphs describe how and when data is
loaded into the output buffer, the types of output data, and their relative priority.
Note that the Meter can also send data to the IEEE-488 bus from the serial poll register.
For a description of this data, see the “Status Data” section later in the manual.