Below is the pinout of the 30-pin connector on the Photon Replicator board. The Replicator Board does only some filtering of the RS-232 signals, so the electrical interface is the same as that of the Tau2. You can use full voltage RS-232 levels or CMOS logic levels (0 to +3.3V) directly from a UART. The Tau2 will only send CMOS logic level signals when it transmits.Unlike the legacy Photon, the Tau2 will automatically adapt to the polarity change when a UART is used directly.
Pinout of Photon Replicator Board