XBee Coordinator API not receiving data from Router AT pin 20
Did you configure the AD0 pin as analog properly? 


If you configured it properly, then it will send the IO sample frame. 
If you did not connect anything to AD0 then it will send garbage value in the IO sample frame. 


A router must have to be configured in API mode to use its analog pin. 

See IO sampling using XBee for more information.