TTL Output Encoder Basic Testing 

This is an easy way to test the basic functionality of one of these encoders. There are many things that can go wrong that this test will not reveal, but if the encoder passes this test, it has not received major damage.
NOTE: The A and B channels are phase shifted by 90 degrees. This allows 4 rising or dropping edges to appear per each encoder count, therefore allowing 4 times the resolution of the basic encoder count if these edges are used for the counting. The complementary channels (/A and /B) are direct inversions of the A and B channels. The addition of these complement channels are what distinguish a differential quadrature encoder from a quadrature encoder. The use of these complementary channels in a differential quad encoder allows for more noise immunity but does not increase the resolution of the encoder.