The standard 9 pins RS232 connector has 9 pins. Those are:
1 -- DCD -- Data Carrier Detected
2 -- RxD -- Receive Data
3 -- TxD -- Transmit Data
4 -- DTR -- Data Terminal Ready
5 -- GND -- Signal Ground
6 -- DSR -- Data Set Ready
7 -- RTS -- Request to Send Data
8 -- CTS -- Clear to Send Data
9 -- RI -- Ring Indicator
A) If I need bi-directional communication it is obvious that I should connect RxD and TxD. What should I do with other signals/pins - connect to ground, left open, need to drive them with appropriate signals according to protocol?
B) If I care only about uni-directional connection can I connect only RxD or TxD?
C) What are the consequences of not using/connecting certain signals. What software on PC side expect to have those signals? What functionality will be lost?
NOTE 1: I am using here word "connect" in sense of logical connection -> for electrical connection I would require level shifter circuitry such as MAX232)
NOTE 2: I am pin limited on uC - I do not mind connecting any signals on the board (like pulling them up/down).