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Channel and Group IDs
Most functions in the HP E1432A 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 HP E1432A modules that will be used.
This function checks the existence of an HP E1432A 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 HP E1432As. 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 theHP 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.
HP E1432A User's Guide
The C-Language Host Interface Library
4-10