Rs232, Sb9600; Battery Id; Radio Audio System; Tx Path - Motorola MTH500 Service Manual

RS232, SB9600

Battery ID

Radio Audio System

68P02963C70-O
The REDCAP processor (RCE) uses the three serial protocols: UART and
SB9600 to communicate with external devices via the bottom connector of the
unit. There is no external hardware for switching from one protocol to another be-
cause the REDCAP2 handles the switching and line multiplexing functions inter-
nally.
The battery is equipped with a Dallas 2502 EPROM. A one-wire serial bus allows
the radio or the battery charger to communicate with the battery and identify
whether or not the battery is compatible. If the battery is determined to be incom-
patible, the unit automatically shuts off, and the charger does not enter charging
mode.
Besides compatibility data, the EPROM also stores the following information:
battery type, capacity, fuel-gauging parameters, and voltage threshold.
See Figure 11.
The audio system consists of the GCAP 3 IC (U600) and the DSP (U401), both
are located on the main board.
The GCAP 3 perform the analog task and part of the digital task of the audio sys-
tem.

Tx Path

Audio speech is fed either to the internal microphone, or to a Phone Hands Free
(PHF) microphone. The signals reach the GCAP 3 IC. In the GCAP 3 IC, a fix gain
amplifier (A3 or A5) provides the signal amplification, the multiplexer (MUX) se-
lects the active input, and the programmable Gain Amplifier (TxPGA) adjust the
path gain according to the radio mode of operation. Finally, the A/D converts the
analog signal into digital format and transfers it to the DSP. The DSP performs the
functions of audio filtering, ACELP speech compression, digital modulation, and
transfers the data to the RF section. When the radio is operating in the telephone
interconnect mode, the DSP performs the required tasks such as echo and noise
reduction.

Rx Path

The digital output signal from the receiver is fed to the DSP which performs the
functions of digital de-modulation, ACELP speech de-compression, and audio fil-
tering. It transfers the data to the GCAP3 IC. In this IC, the D/A converts the dig-
ital audio format to an analog signal, the Programmable Gain Amplifier (RxPGA)
Theory of Operation
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