VXI VT1433B - Manual (Page 88)

Channel and Group IDs
Most functions in the VT1432A C-Language Host Interface Library take an ID
parameter which specifies what channel or group of channels the function should
apply to. The ID can either be a channel ID or a group ID. If a group ID is
used, then the function is applied to each channel contained in the group.
Channel IDs
Channel IDs are logical IDs which are created by a call to
e1432_assign_channel_numbers. The e1432_assign_channel_numbers function
must be called exactly once, following the call to e1432_init_io_driver, in order
to declare to the library the logical addresses of the VT1433B modules that will
be used.
This function checks the existence of a VT1433B module at each of the logical
addresses given in a list of logical addresses and allocates logical channel
identifiers for each channel in all of the VT1433Bs. Input channels, source
channels and tach/trigger channels are kept logically separated. Channel numbers
for each type of channel are numbered starting from one, so there will be input
channels 1 through M, source channels 1 through N and tach/trigger channels 1
through P, where M is the number of input channels, N is the number of source
channels and P is the number of tach/trigger channels.
As an example, suppose two logical addresses 100 and 101 are passed to the
function and the logical address 100 has two 4-channel input SCAs and a
2-channel tach/trigger board, while logical address 101 has three 4-channel input
SCAs and a 1-channel source board. In this case, input channel IDs 1 through 8
are assigned to the eight input channels at logical address 100, while input
channel IDs 9 through 20 are assigned to the twelve input channels at logical
address 101. Tach/trigger channel IDs number 1 and 2 are assigned to the two
tach/trigger channels at logical address 100 and Source channel ID number 1 is
assigned to the source channel at logical address 101.
To use the ID of an input channel, the input channel number is given as an
argument to the E1432_INPUT_CHAN() macro. (For backwards compatibility
with the Agilent/HP E1431A, the macro does nothing.) To use the ID of a
source channel, the source channel number is given as an argument to the
E1432_SOURCE_CHAN() macro. To use the ID of a tach/trigger channel, the
tach/trigger channel number is given as an argument to the
E1432_TACH_CHAN() macro. A channel ID is always positive.
For example, to set the range of the third input channel to 10 volts, the source
code would look something like:
status = e1432_set_range(hwid, E1432_INPUT_CHAN(3), 10.0);
VT1433B User's Guide
The Host Interface Library
4-10