Motorola GP series Manuel - Page 8

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1-4

A MOSFET Q416 switches in the LiO supply when Vdd is removed. Q416 also provides isolation

from BOOT_CTRL function in the event of radio program flashing. The 3.3V regulator charges the

Lithium battery.

3.4

ModB/Vstby Supply

The supply to the ModB/Vstby pin varies depending on the conditions listed in Table 1-2.

Condition

Radio On

Radio Off

Primary battery removed

Flash Mode

3.5

Audio/Signalling Architecture

( Refer to Figure 1-2 and the ASFIC/ON_OFF and Audio Power Amplifier schematic diagrams )

The audio/signalling/filter/companding IC (ASFIC_CMP) and the audio power amplifier, shown in

Figure 1-2, form the main components of the audio/signalling architecture section of the controller

board. Inputs include a 16.8 MHz clock from the synthesizer, recovered audio and squelch, MCU

control signals, and external or internal microphones. Outputs include a microprocessor clock (uP),

modulator output to the synthesizer, and amplified audio signals to an internal or external speaker.

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Table 1-2 ModB/Vstby Supply Modes

Circuit Operation

Vdd supply voltage via CR411

• Vdd turned off

• Q416 gate pulled low by R462

• Q416 switched on

• U410 supplies 3.2V to ModB/Vstby

• Vdd turned off

• Q416 gate pulled low by R462

• Q416 switched on

• Lithium battery provides 3.2V to ModB/Vstby

• Boot_Ctrl line pulled low

• ModA & ModB go low

• Processor in boot-strap mode

THEORY OF OPERATION