Next, we succesfully tested serial transmission and reception from mbed(through 9th & 10th serial port pins).
For testing data transmission, we made use of ebox (as we didn't had PC) that was already available with us. To convert the voltages( ttl to RS-232), we had to make use of MAX 232. The circuit looked as follows:
It must be noted that the PCB shown in the diagram on the right is used only for the usage of MAX232 IC in that circuit(since we didn't have spare IC).