VXI VT1433B - Manual (Page 107)

VT1433B Parameters
Some parameters, such as range or coupling, apply to specific channels. When a
channel ID is given to a function that sets a channel-specific parameter, only that
channel is set to the new value.
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 e1432_preset, all of the parameters
(both channel-specific and global) in an VT1432A 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, VT1433B 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.
There is no way to tell the module 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. Also, there is no way to disable the settling
that takes place at the start of a measurement.
For More Information
Refer to the (on-line) VT1432A Function Reference for a list of all functions and
the parameters needed for each function. (See “Where to get more information” in
the chapter titled “Using the VT1433B”).
VT1433B User's Guide
The Host Interface Library
4-29