Campbell Scientific SDM-CAN Datalogger to CANbus Interface - Manual (Page 33)

SDM-CAN Datalogger-to-CANbus Interface
For some data types this parameter will be overridden by a fixed
number of bits required by the data type; even so the interrupt
setting can still be set. For integer values, the longest integer you
can read or send from one datalogger input location is 16 bits as
a result of limitations within the datalogger (see Section 3.2,
System Limitations, above for an explanation and work-arounds. NOTE
3.3.8 Number of Values (Parameter 11:)
This is the number of values that will be transferred to or from the datalogger
in one operation. For each value transferred, the number of bits (parameter 10)
will be added to the start bit number (parameter 9) when the start point is
referenced to the right-hand side of the data frame. If referenced to the left-
hand side, then the number of bits is subtracted from the current bit position.
The consequence of this is that successive values are always from right to left
in the frame.
3.3.9 Location (Parameter 12:)
This is the start input location where data will be read from or stored to. For
any remaining values/repetition, each value will be read from, or stored into,
the next incremental location.
3.3.10 Multiplier (Parameter 13:)
The data written to, or read from, an input location is multiplied by this
parameter.
3.3.11 Offset (Parameter 14:)
The data written to, or read from, an input location has this offset parameter
added to it.
3.4 Advanced Programming Techniques
3.4.1 Interrupts Using the I/O Connection
The I/O port can be used to signal to a datalogger that specific data has been
captured, by the SDM-CAN, from the CAN network and is available for
collection by the datalogger.
The main application for this is where CAN data needs to be captured at a
much faster rate than the normal scan interval of the datalogger and the
requirement is to capture as many CAN packets as possible. In this case the
interrupt facility can be used to give capture of the CAN data as a higher
priority over the normal scheduled measurement tasks, allowing the data to be
captured at the highest rate possible.
The interrupt facility can also help solve the conceptual problem of capturing
data into the datalogger from another system (one of the other devices on the
CAN-Bus) which is running on a different asynchronous clock from the
datalogger itself. This problem needs some consideration in all applications
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