you may find a post HERE but it does not work, so follow the steps below:
1. connect the TTL serials without GND pin;
2. keep holding Ctrl+C on the keyboard, may need a guy to do this;
3. make sure the router is power-off;
4. power on the router;
5. wait for 0.5 second and QUICKLY connect the GND pin;
6. then you'll see the CFE console.
7. if not, do step 3~6 again :-)