This is a wiring diagram that [Soranne] put together when developing a method of programming PIC microcontrollers using an Arduino board. You can see that he takes care of the 12V issue by connecting ...

If you doesn't have TTL (Transistor-Transistor Logic) USB and want to do Rx-Tx transmission. Don't worry you can use us arduino. From simple hardware modification you can use your Arduino as USB TTL ...