The front panel uses I2C to communicate with the main board, the connector on main board is J702.

Pin out for J702:

Pin | Function
--- | ---
Pin1 |     Keypress @ Keypad U26 Pin 43 P5.7 (Goes active high on kepress)
Pin2 |     unknown  @ Keypad U26 Pin 51 P1.2 (seems always low)
Pin3 |     unknown  @ Keypad U26 Pin 45 P2.0 (seems always low)
Pin4 |     +3.3V
Pin5 |     +3.3V
Pin6 |     GND
Pin7 |     SDA to/from Keypad U26 Pin 50 P1.3 & U800 EEprom Pin 5
Pin8 |     unknown  @  Keypad U26 Pin 46 P1.7
Pin9 |     SCL to/from Keypad U26 Pin 49 P1.4 & U800 EEprom Pin 6
Pin10 |     GND  

Hantek HDG2002B AWG Front Panel KeyPad Protocol
-----------------------------------------------
I2C Protocol on J702 pins 7 (SDA) & 9 (SCL)

Read  - Key ScanCode = 0x55 + (Keycode Byte)
Write - LED State    = 0x55 + (LEDcode Byte)