I find it pays to condition the TxData line first. For true RS232, i.e. using a MAX232 for example, the following works a treat.

HIGH PortB.2 : Pause 5
Serout PortB.2,N2400,["This is a test ", #i,10,13]

This forces the RS232 interface into the correct MARK state where the external line to the terminal device idles low at negative 6~12 volts. The Start bit, a SPACE, is then seen as a positive going bit.

HTH
BrianT