Serial line on J1, pin 1 is boxed, 6 GND, 5 is router's TX and 4 is RX, baud rate is 38400.
after error “sys checksum error at 00030000!”, the router won't boot. You can still use ipconfig 192.168.0.55 (or similar) to setup an IP address and flash the device (if you were holding reset on startup). Remember, that the router only listens on the socket closest to the power jack.