VXI VT1433B - Manual (Page 45)

Channels and groups
This section gives some information about using channels and groups. For more
detailed information see the VT1433B help text.
Channel Groups
In the VT1433B VXIplug&play driver, a channel group is the basic unit of
hardware control. To control any channel, it must first be assigned to a group
with the hpe1432_createChannelGroup function. In addition to creating the group,
this function returns a “handle” that uniquely identifies the group. This handle
can then be used to direct functions to all channels in the group.
When a channel group is created, all input and tach channels in the group are
automatically activated and all source channels are inactivated. But when deleted,
input and tach channels are not automatically inactivated. Any input or tach
channel that remains active after its group is deleted will continue to supply data
to its module’s FIFO buffer during a measurement — consuming module
resources. For this reason, the channels in group should always be explicitly
inactivated before deleting them. Channels can be inactivated with
hpe1432_setActive. Channel groups can be deleted with
hpe1432_deleteChannelGroup and hpe1432_deleteAllChanGroups.
Also when creating a channel group, channels which are not mentioned in the
new group are not turned off. Any channels that are not to be active must be
explicitly inactivated. (An exception is a power-up when only the channels in the
initial channel group are active.)
Initialization
The command used to initialize the system is hpe1432_init. This function
initializes the VXIplug&play library and registers all VT1433B modules. It also
checks the existence of a VT1432A module at each of the logical addresses given
in the resource list and allocates logical channel identifiers for each channel in all
of the VT1432As. Input channels, source channels and tach/trigger channels are
kept logically separated.
Most other functions cannot be used until after hpe1432_init, but there are two
functions which can be used before initialization to get information needed by
hpe1432_init. These are hpe1432_find and hpe1432_getHWConfig. hpe1432_find
searches the VXI mainframe and returns the VXI Logical Address for every
VT1433B found. hpe1432_getHWConfig returns additional information about the
hardware.
After hpe1432_init is run, use hpe1432_getNumChans to get the total count of
inputs, sources and tachometers for all VT1433B modules named in the
hpe1432_init call.
VT1433B User's Guide
Using the VT1433B
3-7