Usart Tx pin goes bad ! Need help

Hi All,

I am having Stm32F030 controller where i am using half duplex communication in Usart using Tx pin. Half duplex communication works good. But sometimes Tx pin goes bad(getting short with ground). I am not aware of this problem , can anyone please suggest where i am wrong.

Tests conducted::
Cross checked the pcb track for any problem, it is okay.
For successful communication, Tx pin is pulled up by 4.7K resistor.

Based on experience with PICs and AVRs, floating input pins may cause disturbance in UART. If you bring your fingers near chip, they ca pic the electrical charge from the body. Or air.

Try as well 10K as a pull up.

How do you know there is a short? Or it is just simply in a 0 logic state?

1.I have checked the Tx pin of the controller using multimeter to Ground , it gives dead short.
2.In some other board TX pin does not have short to ground but Tx pin fails to perform half duplex communication.
For confirming point 2 , did a simple TX pin toggling application(TX pin has a alternate function of GPIO) but even that also fails to perform.
3. I am aware static energy so we are using controllers with care, I have a pull up resistor of 10K connected to TX pin of the micro controller to perform half duplex communication .

Is there any other cause for this problem, please help.