96 Circuit Descriptions TM8100/TM8200 Service Manual© Tait Electronics Limited November 20073.9 Control-Head Board with Graphical DisplayIntroduction This section describes the control-head board for the control head withgraphical display.For a block diagram of the digital circuitry, refer to Figure 3.15.Most signals (except power on/off, speaker and microphone) to and fromthe radio body are processed by a RISC processor, which is implemented onan FPGA on the control-head board. For more information on the RISCprocessor and the FPGA, refer to “Software Architecture” on page 49.User Interface The control-head board includes the circuitry for the following controlelements:■ ON/ OFF key■ volume potentiometer■ main keypad (with four functions keys, two scroll keys andtwo selection keys)■ LCD module (with backlighting and optional heating element)■ three status LEDs■ two function key LEDs (for function keys F1 and F4)■ keypad backlighting LEDs■ speaker.Connectors The control-head board includes the circuitry for the following connectors:■ microphone connector (RJ45 socket)■ control-head connector (18-way MicroMaTch socket)■ LCD connector (for internal connection of LCD module)■ speaker connector (2 leads)■ soldering pads (2 leads) for an optional concealed microphone■ control-head options connector (for optional circuit board).Protection circuitry is provided for the microphone connector. For pinoutsof the control-head connector and the microphone connector, refer to“Connectors” on page 38. For more information on the control-headoptions connector, please contact Tait Electronics Limited.ON/ OFF Key When battery power (13.8V) is applied to the radio, a press of the ON /OFF keywill create an active low signal (CH ON OFF) back to the radio body to initiatethe power-on or power-off sequence. This key-press will also be detectedby the FPGA of the control head through Q611 as an active high signal.For more information on the start-up process, refer to “SoftwareArchitecture” on page 49.
