AT48LC4M32B2 AT48U54B-01 AT-49 16.0000MHZ 10PPM AT-49 17.73MHZ AT-49 19.6609MHZ AT-49 28.6364MHZ AT-49 3.6864MHZ AT-49 4.500MHZ AT-49 4.608MHz AT-49 40.680MHz