What this 2 x 4:1 mux/demux does on the board
The SN74CBT3253DR is a dual 4:1 multiplexer/demultiplexer from TI's 74CBT family — it routes one of four input signals to a common output, or splits a common input to one of four outputs, across two independent channels. Housed in a 16-SOIC (3.90 mm width) package, it mounts on the board with a standard 1.27 mm pitch footprint — rework-friendly under hot air, with pin 1 clearly marked at the chamfered end.