Fluke 8845A - Input;Output and Triggering

Digital Multimeter
How the Meter Processes Output
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How the Meter Processes Output
The following paragraphs summarize how the Meter processes output. The Meter outputs
an alphanumeric string in response to a query command from the host. Query commands
are easily identified because they all end with "?". An output string is terminated by a
Carriage Return and Line Feed (<CR><LF>) for RS-232 or Ethernet applications, or a
Line Feed with End or Identity (<LF><EOI>) for IEEE 488.
After sending the Meter a query command via the RS-232 interface, wait for the Meter to
return a prompt before sending another query command. Although the Meter will accept
and process all commands other than a query command, a device-dependent command
error is generated; and the second command is discarded if it is a query command.
If the Meter is part of an IEEE 488 bus system, the output data is not actually sent onto
the bus until the host addresses the Meter as a talker. When the output buffer is loaded,
the Message Available (MAV) bit in the Status Byte Register is set true. (For more
information, see "Status Byte Register.”)
Numeric output from the Meter is displayed as shown in the following examples:
EXAMPLE EXPLANATION
+1.2345E+0 Measured value of 1.2345
+1.2345E+6 Measured value of 1.2345 x 10
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Triggering Input
While under remote control, the Meter must be placed in a wait-for-trigger state before a
measurement can be triggered. The INITiate and READ? commands set the Meter in to a
wait-for-trigger state. The number of measurements (samples) and the number of triggers
the Meter will accept after being put in a wait-for-trigger state are variables set using
remote commands. The defaults for these variables are one sample per trigger and one
trigger per wait-for-trigger state. See the Trigger and Sample remote commands to set
these values.
All available trigger methods fall into two basic categories:
• Internal triggering uses the Meter’s internal trigger circuit for a continuous source of
triggers.
• External triggering comes from a source outside the Meter controlled by the user.
Internal Triggering
When the Meter’s trigger source is set to immediate, measurements are triggered by the
Meter’s internal trigger circuit. As an example, with the sample count set to 5 and the
trigger count set to 2, the Meter will collect 10 measurements after it receives an INITiate
or READ? command and then stop taking measurements. The READ? command will
return all 10 readings immediately while the INITiate command must be followed by a
FETCh? command to retrieve the measurements.