Telem port no output

Hi, I have connected pixhawk 2.4.8 through micro USB to PC to power up. When I power up using micro USB connector I get ttyACM0 installed on my PC and I can receive mavlink data through this port. However, no data is sent by pixhawk on telem1 and telem2 ports which I connect to my PC on serial ports ttyS0 and ttyS1.
Is there any configuration I am missing or when powered through micro USB cable telem1 & 2 ports are disabled.