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S:\agilent\8920\8920b\PRGGUIDE\BOOK\CHAPTERS\guidelin.fb
Chapter 3, GPIB Command Guidelines
Sequential and Overlapped Commands
Sequential and Overlapped Commands
IEEE 488.2 makes the distinction between sequential and overlapped commands.
Sequential commands complete their task before execution of the next command
can begin. Overlapped commands can run concurrently, that is, a command
following an overlapped command may begin execution while the overlapped
command is still in progress. All commands in the Test Set are sequential.
The processing architecture of the Test Set allows it to accept commands through
the GPIB while it is executing commands already parsed into its command buffer.
While this may appear to be overlapped, commands are always executed
sequentially in the order received.
The process of executing a command can be divided into three steps:
1. Command is accepted from GPIB and checked for proper structure and parameters.
2. Commands is sent to instrument hardware.
3. Instrument hardware fully responds after some time,
∆
t.
For example, in programming the Test Set’s RF Signal Generator it takes
< 150 ms after receipt of the frequency setting command for the output signal to
be within 100 Hz of the desired frequency. In the Test Set, commands are
considered to have “completed their task” at the end of step 2. In manual
operation all displayed measurement results take into account the instrument
hardware’s response time. When programming measurements through GPIB the
Triggering mode selected will determine whether the instrument’s response time
is accounted for automatically or if the control program must account for it. Refer
to
“Triggering Measurements” on page 224 for a discussion of the different Trigger
modes available in the Test Set and their affect on measurement results.