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Some parameters, such as clock frequency or data transfer mode, apply globally
to a module. When a channel ID is used to change a parameter that applies to a
whole module, the channel ID is used to determine which module. The parameter
is then changed for that module.
Starting and stopping a measurement is somewhat like setting a global parameter.
Starting a measurement starts each active channel in each module that has a
channel in the group.
After firmware is installed and after a call to hpe1432_preset, all of the
parameters (both channel-specific and global) in a VT1433B module are set to
their default values. For channel-specific parameters, the default value may
depend on the type of channel. Some channel-specific parameters apply only to a
specific type of channel. For example, tach holdoff applies only to tach channels.
Setting such a parameter for a channel that doesn’t make sense will result in an
error.
At the start of a measurement, the VT1433B firmware sets up all hardware
parameters and ensures that the input hardware is settled before starting to take
data. The firmware also ensures that any digital filters have time to settle. This
ensures that all data read from the module will be valid.
However, after a measurement starts, VT1432A parameters can still be changed.
The effect of this change varies, depending on the parameter. For some
parameters, changing the value aborts the measurement immediately. For other
parameters, the measurement is not aborted, but the changed parameter value is
saved and not used until a new measurement is started. For still other parameters,
the parameter change takes place immediately and the data coming from the
module may contain glitches or other effects from changing the parameter. For
more information, please see the “Programming Information” chapter of the
VT1433B VXIplug&play Library online help.
The module cannot be told to wait for settling when changing a parameter in the
middle of a measurement. The only way to wait for settling is to stop and
re-start the measurement. The settling that takes place at the start of a
measurement also cannot be disabled.
Refer to the (on-line) VT1433B Function Reference for the parameters needed for
each function. (See “Where to get more information” in this chapter.)
VT1433B User's Guide
Using the VT1433B
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