 There are many different signal routing boards that could be used with a single target board, depending on what device is in the ZIF socket.The STK600 allows in-system programming from the PC via USB, leaving the RS-232 port available for the target microcontroller.A 4 pin header on the STK600 labeled 'RS-232 spare' can connect any TTL level USART port on the chip to an onboard MAX232 chip to translate the signals to RS-232 levels.