SM-EW90-B 5-Port Cockpit Junction Box connects up to 2 pairs of Di2 shifters to the frame junction box via 5 SD50 E-tube wires. This allows for multiple shifting options including climbing, sprint or TT/Tri.
All Di2 components on the bicycle require the same firmware version. Using Di2 components with different firmware versions may cause malfunctions. Use Di2 system checker to update component firmware from http://e-tubeproject.shimano.com/