Both are related. The RS232 protocol says that the line stays inactive at -12volt and the TTL output is at 5V at the same time. This forces you to have the appropriate inverter driver chip like MAX232 for example.

If you do not want to use that chip then you have to make your TTL output stay at 0Volts to fool RS232 line and if you are lucky (as is the case most of the times) the other end of the RS232 line will understand that TTL output is idling.

Hope this makes sense now.

Ioannis