Fluke 8845A Manual page 98

8845A/8846A
Programmers Manual
becomes full. The only valid input terminators are CR, LF, GET (Group Execute
Trigger), and/or EOI.
When the Meter receives an input terminator, it executes the previous commands in the
order in which they were received. As input characters are processed and executed,
space is made available in the input buffer for new characters.
If the input buffer becomes full, the Meter stops accepting characters from the bus until
all complete command strings currently in the input buffer have been executed. In this
way, characters sent to the Meter are never lost due to buffer overflow.
In some instances, a terminator is automatically transmitted at the end of the controller's
output string. For example, in Fluke BASIC, the PRINT statement always finishes with a
CR LF pair. If a controller does not have this feature, the programmer must transmit a
terminator explicitly.
The Meter accepts alphabetic characters in either upper or lower case. Spaces, commas,
and control codes are ignored and are not placed in the input buffer. If the Meter
receives a group of terminators (such as CR LF or CR LF EOI), only a single
terminator is loaded into the input buffer. Numeric values used in PUT commands may be
in NR1, NR2, or NR3 format as described in the IEEE-488 Codes and Formats
Recommended Practice. (These correspond to the signed integer, real number, and real-
number-with exponent formats described under the N command).
Illegal commands (e.g., F9) generate an error message, but are otherwise ignored, and do
not affect the instrument's configuration.
Example
"* F9"
Syntax Rules
Four syntax rules should be followed when constructing input command strings. They
are:
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RULE 1: Read output data only once.
To prevent old (previously read) data from being read a second time by mistake, the
output buffer is always cleared after it has been read. If the output buffer is read twice
without an intervening output command, the Meter will not respond to the second
attempt to read the output buffer. (However, if the Meter is in T0, no intervening
command is necessary.)
RULE 2: Use no more than one output command per input command string.
Because the Meter has only one output buffer, it writes new data over old. If an input
command string contains more than one output command, only the data from the last
command can be read.
Example
"F1 T3 ? F2 ?"
"F2 R3 S0 T3 ?"
"F2 R3 S0"
Explanation
This would load the output buffer with an error
message and select F1 (established by the * command).
Explanation
Improper construction. The second trigger writes over
the first. To obtain two readings, send two complete
command strings (separated by terminators).
Correct construction. The string contains only one
output command.
Correct construction. It is permissible for a string not
to contain an output command.