The trigger commands are as follows;
“CT” Configure Trigger
“TR” Execute Trigger Buffer
The configure trigger
command
is followed by a string of any Generator programming
commands up to 71 characters in length.
The validity of the programming commands is not
checked until the trigger buffer is executed. The power-on value of the trigger string is null
(nothing).
The trigger command causes execution of the trigger buffer, which has been preprogrammed
with
the configure trigger command “CT”. The trigger buffer can also be executed
by
sending
the IEEE-488 group execute trigger interface message (GET).
The following paragraphs describe how IEEE-488 commands are processed by
the Generator.
Command processing is a term for how commands are executed and how errors are handled.
2-63.
COMMAND EXECUTION
The execution of the IEEE-488 commands depends on the selection of interface modes with
one exception; if an IEEE-488 input is buffered and the buffer becomes full, command
execution starts and no further input is accepted until there is room in the input
buffer.
For
more details, refer to the paragraphs on Interface Modes.
2-64.
ERROR
HANDLING
The Generator detects two types of errors while processing IEEE-488 commands; syntax
errors and processing errors. All errors are accumulated until the error
status
is interrogated or
is explicitly cleared. The IEEE-488 rejected entry status is interrogated with the “IR”
command. The error status is cleared with one of the following commands:
“CE” Clear
Error Command
“CL” Clear Command
“DCL” or “SDC” Clear Interface
Messages
The error status is also cleared at power-on.
The SRQ mask
can
be
set
to assert SRQ when
an
error is detected, The SRQ is unasserted
when the error status is cleared.
Syntax errors are commands that do not have the correct syntax for the specified header.
For
example, “FES” is a syntax error because the external FM command requires a Boolean
numeric field. Unrecognized headers are
also
syntax errors. An IEEE-488 syntax error causes
all commands from the point of the error up to the next string terminator or record
terminator
to be ignored.
Processing errors are
commands that are syntactically valid, but the requested value is outside
the range of programmable
values.
For
example, “FR99GZ” is syntactically correct, but the
Generator cannot be programmed to a frequency of
99
gigahertz.
Command processing
continues with the next
command.
2-65.
Timing Data
The programming time can
be broken down into four-groups: transfer of commands to
Generator,
command parsing time, software programming time, and instrument
settling time.
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