How to get Beaglebone Black serial debug information

I’m new in beaglebone black. I know in original version beaglebone, I can get serial debug information just plugging mini usb to pc. But Beaglebone black can’t. I search from http://circuitco.com/support/index.php?title=BeagleBone_Black_Accessories and try to use Adafruit 4 Pin Cable (PL2303) by plugging green line to P9-4, white line to P9-5, black line to GND. I use putty trying to get serial information but I can get only much of disorder and non-meaningful characters just like setting wrong baud-rate. But I don’t know why I set 115200 in putty and it work in original version beaglebone. How can I get right serial debug information in Beaglebone Black. Thanks.

http://circuitco.com/support/index.php?title=BeagleBone_Black_Serial

Gerald