I want to use Cobra Board to control SM5100B CELLULAR SHIELD. I connect TX/RX to Cobra’s COM1 and connect VIN to 3.3v on the Cobra board. Then connect ground to ground.
However, I test the Serial Port, then it shows the error is the Serial Frame Error.
Is any body could help me ? 
If you are getting a frame error then it sounds like you have a serial parameter mismatch.
You should insure that the baud rate, number of data bits, parity and number of stops bits match the device requirements.
Usually, it helps to post your code.
Thanks. I will try.