An IODDT allows all information (bits and registers) related to a channel to be handled through a user-defined variable. This variable is defined in the Control Expert data editor by selecting the appropriate IODDT for the module as a data type and specifying the topological address of the module using the following syntax:
%CH[\b.e\]r.m.c
where:
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b = bus
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e = equipment (drop)
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r = rack
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m = module slot
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c = channel
Here is an example of an IODDT for a thermocouple input module in slot 4 of a local rack:
Variables in the User Program
You can access all information related to channel 1 of the module using the following variables:
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My_Temp_Point1.VALUE for the measured value
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My_Temp_Point1.ERROR indicating an out-of-range condition
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My_Temp_Point1.WARNING indicating an over-range condition
