TRS3232E-Q1: How do we handle unused driver/receiver terminals and do we need external OPAMP?

Unused outputs can be left open. Unused inputs must not float; the RIN pins have internal pull-down resistors and can be left open, while the DIN pins must be connected to V_CC or GND.

You would not use opamps for digital signals. The RS-232 I/Os conform to the RS-232 specification; the logic I/Os are designed to be connected to a microcontroller. You would need separate buffers only if you had some additional load (larger than 1 mA) on the ROUT pin.

Hi Ochi,

I support Clemens answer. Unused outputs (DOUT, ROUT) can be left floating. RIN pins have internal 5kohm pull-down resistors and can be left open. DIN pins need to be tied to VCC or GND. 

TI's RS-232 portfolio follows the RS-232 standard. The reason for external capacitors on the device is to setup the charge pump circuitry to be able to output +V and -V voltage levels per RS-232 standard. You should not need external amplifier circuitry on driver/receiver IN/OUT, the device already does the voltage conversions for you. Clemens makes a good point about external buffering if you were driving a digital load larger than 1mA on the ROUT pin. You should follow the current specifications for the driver/receiver IN/OUT. 

Regards,

Tyler