Fluke 9640A Series, Instruction Manual

Page: 159 / 324

SCPI Commands
Coupled Commands
4C
4C-23
Coupled Commands
What Is Command Coupling?
Commands from the IEEE interface bus are usually executed serially in the order they are
received. However, because commands may come in any order in a command string, it is
possible that a combination of commands produce an illegal machine state if executed in
isolation, but a valid machine sate if executed collectively.
This problem is overcome by defining a coupling between commands which allows the
execution of individual components to be deferred until all contiguous coupled
commands in the same group have been parsed and the validity of the combinations
checked.
Note
Individual commands may be a member of several coupled command
groups.
A good example is power and frequency. Either of these commands could be used
individually to configure an instrument (with the other parameter assumed or defaulted).
However, there are instances when both commands are required together before the
requested configuration is valid.
Suppose the instrument has a profile that allows high frequency at low power and high
power at low frequency. Assume the instrument is currently set to a high frequency, low
power and we require a change to give high power, low frequency. Manually, we would
have to reduce the frequency before we could increase the power.
On the bus, if the power command is sent before the frequency command and the
commands were processed as they were received, then an error would be reported as the
instrument would think that a high power AND a high frequency were being requested.
See Figure 4C-1.
Power
Frequency
+10 dBm
1MHz
Starting
Point
200MHz
20 dBm
Requested
Point
Invalid
Point
Bus commands without coupling
:POWer +10 ;:FREQency 1E6
ead123f.eps
Figure 4C-1. Bus Command without Coupling