Some people might wonder: what is the pinout of my router’s serial connection. If you’re a happy owner of TP-Link TD-W8901G and asking that yourself, here is the answer:
In the link below there is also this router’s pinout and moreover author states that to make that port working there is a need to modify some resistors. I have V3.5 of that router and didn’t notice any mod to be necessary.
It is possible to solder goldpins in here and router so far haven’t fried. Of course you can try communicating without stable connection and it even works but after training your fingers while waiting for the firmware download/upload to complete you’ll change your mind, I guarantee:).
PS2: if you have another router and want to find out what is the serial port pinout I recommend going here.