DToA:

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   Converts a digital word to a voltage.
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   Form:
   v = DToA( c, b, vMax, vMin )
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   ------
   Inputs
   ------
   c   	        (:)     Commands
   b             (:)     Maximum counts (8 bit = 256)
   vMax          (:)     Maximum voltage                      
   vMin          (:)     Minimum voltage                      

   -------
   Outputs
   -------
   v   	      (:)     Voltage

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