Demonstrations for PGA operation.

1. Compare P port and N port input voltage, if P port is bigger than N port,
   the compare status will be set.
   Pin Usage : PGA0_INP0:XPA5
               PGA0_INN0:XPA4
               PGA0_OUT :XPA3

2. Amplify P port voltage with internal amplify circuit.
   Pin Usage : PGA0_INP0:XPA5
               PGA0_INN0:XPA4
               PGA0_OUT :XPA3

   Feedback gain : 8
