Why can't I successfully send messages over RS232?
You have missed a major detail of RS232. Logic levels are as follows:



Figure 1. RS232 signal levels. Source: Wikimedia Commons.


Logic 1 = -3 to -12 V.
Logic 0 = +3 to +12 V.
Between -3 and +3 the logic level is undefined.
The RS232 start bit is a logic 0.


To convert from TTL (5 V) logic to RS232 a driver is required. Chips such as the MAX232 do the logic level inversion and voltage boost for you.

It is possible to "cheat" sometimes and feed a TTL signal into an RS232 input provided the logic level is inverted. The reliability of this method depends on the chip used on the RS232 input.



Figure 2. The transmitted waveform. On top is the bit pattern of the'Q' that you transmitted. On the bottom is how the RS232 input read it.

Note that the RS232 input is looking for a positive edge to indicate the start bit. This doesn't happen until the second bit of your data so everything thereafter is one bit to the right and inverted as the receiver sees it. As luck has it your MSB is the correct logic level for the stop bit so the receiver interpreted it as a valid frame, decoded it and displayed a 'W'.

For test purposes you can invert your TTL output. This will probably work as it is "working" at the moment.



Figure 3. The MAX232 chip uses capacitors in charge pump circuits to boost the 5 V supply for RS232 levels.

For reliability add a MAX232 chip to transmit and receive a proper RS232 level signal.