The 853S54I-01 is a 2:1/1:2 Multiplexer. The 2:1 Multiplexer allows one of 2 inputs to be selected onto one output pin and the 1:2 MUX switches one input to one of two outputs. This device may be useful for multiplexing multi-rate Ethernet PHYs which have 100Mbit and 1000Mbit transmit/receive pairs onto an optical SFP module which has a single transmit/receive pair. A 3RD mode allows loop back testing and allows the output of a PHY transmit pair to be routed to the PHY input pair. For examples, please refer to the Application Block diagrams on pages 2-3 of the data sheet. The 853S54I-01 is optimized for applications requiring very high performance and has a maximum operating frequency in 2.5GHz. The device is packaged in a small, 3mm x 3mm VFQFN package, making it ideal for use on space-constrained boards.