2-8 Controlhead Model for GM338
Line PTT IRDEC (J0811-6) is used to key up the radio’s transmitter. While the PTT button on a
connected microphone is released, line PTT IRDEC is pulled to +5 volts level by R0843. Transistor
Q0843 is switched on and causes a low at µP port PA2. When the PTT button is pressed, signal
PTT IRDEC is pulled to ground level. This switches off Q0843 and the resulting high level at µP port
PA2 informs the µP about the pressed PTT button. The µP will inform the host radio about any
status change on the PTT IRDEC line via SBEP bus.
When line PTT IRDEC is connected to FLT A+ level, transistor Q0821 is switched on through diode
VR0821 and thereby pulls the level on line ON OFF CONTROL to FLT A+ level. This switches on
the radio and puts the radio’s µP in bootstrap mode. Bootstrap mode is used to load the firmware
into the radio’s flash memory (See controller sub section for more details).
The HOOK input (J0811-3) is used to inform the µP when the microphone´s hang-up switch is
engaged. Dependent on the CPS programming the µP may take actions like turning the audio PA on
or off. While the hang up switch is open, line HOOK is pulled to +5 volts level by R0841. Transistor
Q0841 is switched on and causes a low at µP port PA1. When the HOOK switch is closed, signal
HOOK is pulled to ground level. This switches off R0841 and the resulting high level at µP port PA1
informs the µP about the closed hang up switch. The µP will inform the host radio about any status
change on the HOOK line via SBEP bus.
3.9 Speaker
The controlhead contains a speaker for the receiver audio. The receiver audio signal from the
differential audio output of the audio amplifier located on the radio’s controller is fed via connector
J0801-10, 11 to the speaker connector P0801 pin 1 and pin 2. The speaker is connected to the
speaker connector P0801. The controlhead speaker can be disconnected if an external speaker,
connected on the accessory connector, is used.
3.10 Electrostatic Transient Protection
Electrostatic transient protection is provided for the sensitive components in the controlhead by
diodes VR0811 VR00812 VR0816 - VR0817. The diodes limit any transient voltages to tolerable
levels. The associated capacitors provide Radio Frequency Interference (RFI) protection.
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