Motorola GM1280 Service-informatie - Pagina 18

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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 Q0851 is switched on through diode

VR0851 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 R0883. Transistor

Q0872 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 R0883 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.

4.10

Speaker (Remote Mount Conﬁguration only)

The remote mount 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 only an external

speaker, connected on the accessory connector, should be used. If the controlhead is mounted

directly on the radio, an external speaker is required.

4.11

Electrostatic Transient Protection

Electrostatic transient protection is provided for the sensitive components in the controlhead by

diodes VR0811 - VR0814. The diodes limit any transient voltages to tolerable levels. The associated

capacitors provide Radio Frequency Interference (RFI) protection.

THEORY OF OPERATION