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CC Technical Documentation System Module

RM-11

Figure 11: Digital interface of audio amplifier

Figure 12: Block diagram of audio amplifier

The LM4855 features a 32-step, digital volume control and eight distinct output modes.

The digital volume control and output modes are accessed through a 3-wire interface

controlled by the UPP. Digital volume control is needed when the FM radio is activated;

there is no amplifier block in the FM radio module. Output modes are needed when

routing audio to different locations (i.e., headset, IHF).

External Audio Connector

The RM-11 is designed to support a fully differential external audio accessory connection

by using a Tomahawk system connector. The Tomahawk connector has a serial data bus

called Accessory Control Interface (ACI) for accessory insertion and removal detection,

identification, and authentication. The ACI line is used for accessory control purposes

and includes the following:

• 4-wire fully differential stereo audio (used also FM-radio antenna connection)

• 2-wire differential mic input

UPP8M

LM4855

Enable

Clock

Data

DATA

CLK

GenIO(14)

GenIO(16)

GenIO(15)

Output

Mode

Select

Digital

Volu me

Control

SPI

Bias

By pass

Ri n

Li n

EN CL K DAT A

Lout -

Lout +

Rout -

Rout +

out -

out +

VB AT

GN D

Phone

audio

1uF

Radio audio

IH F Spea ker

Radio audio

Stereo

Headset

Amplifier

LM4855