Motorola pro7100 Manuel de service Page 54

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2-40 Theory of Operation
The two A/D converter inputs (J0811-9/10) are used as a microphone with keypad. A pressed key
changes the dc voltage on both lines. The voltages depend on which key is pressed. The µP
determines, from the voltage on these lines, which key is pressed and sends this information to the
host radio.
Line PTT IRDEC (J0811-6) is used to key up the radios transmitter. While the PTT button on a
connected microphone is released, line PTT IRDEC line is pulled to a +5 volts level by R0843.
Transistor Q0843 is then switched on causing 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 informs the host radio about any
status change on the PTT IRDEC line via the SBEP bus.
When line PTT IRDEC is connected to FLT A+ level, transistor Q0821 is switched on through diode
VR0821 pulling the level on the 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.
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 causing 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 informs the host radio about any status change on
the HOOK line via SBEP bus.
2.11.9 Speaker
The control head 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, pins 1 and 2. The speaker is connected to the
speaker connector P0801. The control head speaker can only be disconnected if an external
speaker, connected on the accessory connector, is used.
2.11.10Electrostatic Transient Protection
Electrostatic transient protection is provided for the sensitive components in the control head by
diodes VR0811 VR00812 and VR0816 - VR0817. The diodes limit any transient voltages. The
associated capacitors provide radio frequency interference (RFI) protection.
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