The T2_IN input is CMOS/TTL logic input and should not be left unconnected. Connect T2IN to ground, and leave T2OUT unconnected. In general TTL/CMOS logic inputs should never be left unconnected because the voltage at the pin can drift due to leakage current which will increase quiescent current as the voltage approaches the logic threshold. Driving a CMOS input rail-to-rail minimizes quiescent current.
Similarly R2IN is a RS232 input and should be grounded while R2OUT should be left unconnected.