ADS1271EVM-PDK: Can't detect the input signal


I am a customer of ADS1271EVM-PDK,I connect the MMB0 board with 1271EVM and power the system with DC 6V .

when I connected this system with PC(OS:windows XP) ,It was shown that "Firmware loaded and ready" on status item of ADS 1271 user interface .

But when inputed signals from J4 on 1271EVM, I couldn't get the signal from user interface .

For this input connector, I connected "A1+","A1-"and"GND" wires with the signal source and kept the "AR1+","AR1-" open.

What should I do next? Thanks.