MT9196AS datasheet(4/38 Pages) MITEL

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MT9196

Preliminary Information

7-130

Overview

The functional block diagram of Figure 1 depicts the

main operations performed by the MT9196 IDPC.

Each of these functional blocks will be described

individually in the sections to follow. This overview

will describe some of the end-user features which

may be implemented as a direct result of the level of

integration found within the IDPC.

The main feature required of a digital telephone is to

convert the digital Pulse Code Modulated (PCM)

information, being received by the telephone set, into

an analog electrical signal. This signal is then

applied to an appropriate audio transducer such that

the information is finally converted into intelligible

acoustic energy. The same is true of the reverse

direction where acoustic energy is converted first

into an electrical analog and then digitized (into

PCM) before being transmitted from the set. Along

the way if the signals can be manipulated, either in

the analog or the digital domains, other features

such as gain control and signal generation may be

added. Finally, most electro-acoustic transducers

(loudspeakers) require a large amount of power if

they are to develop an acoustic signal. The inclusion

of audio amplifiers to provide this power is required.

The IDPC features complete Analog/Digital and

Digital/Analog conversion of audio signals (Filter/

CODEC) and an analog interface to electro-acoustic

devices (Transducer Interface). Full programmability

of the receive path and side-tone gains is available

to set comfortable listening levels for the user.

Transmit path gain control is available for setting

nominal transmit levels into the network. A digital,

anti-feedback

circuit

permits

both

the

handset

microphone and the speaker-phone speaker to be

enabled at the same time for group listening

applications.

This anti-feedback circuit limits the

total loop

gain there

by preventing a singing

condition from developing.

Signalling in digital telephone systems, behind the

PBX or standard ISDN applications, is handled on

the D-channel and generally does not require DTMF

tones. Locally generated tones, in the set, however,

can be used to provided “comfort tones” or “key

confirmation” to the user, similar to the familiar

DTMF tones generated by conventional phones

during initial call set-up. Also, as the network slowly

evolves from the dial pulse/DTMF methods to the D-

Channel protocols it is essential that the older

methods be available for backward compatibility. As

an example, once a call has been established (i.e.,

from your office to your home) using the D-Channel

signalling protocol it may be necessary to use in-

band DTMF signalling to manipulate your personal

answering machine in order to retrieve messages.

Thus the locally generated tones must be of network

quality. The IDPC can generate the required tone

pairs as well as single tones to accommodate any in-

band signalling requirement.

Each of the programmable parameters within the

functional blocks is accessed through a serial

microcontroller port compatible with Intel MCS-51®,

Motorola

SPI®

and

National

Semiconductor

Microwire® specifications.

Functional Description

In this section each of the functional blocks within

IDPC is described along with all of the associated

control/status bits. Each time a control/status bit(s) is

described it is followed by the address register

where it will be found. The reader is referred to the

section titled 'Register Summary' for a complete

listing of all address registers, the control/status bits

associated with each register and a definition of the

function of each control/status bit. The Register

Summary is useful for future reference of control/

status bits without the need to locate them in the text

of the functional descriptions.

Filter/CODEC

The Filter/CODEC block implements conversion of

the analog 3.3 kHz speech signals to/from the digital

domain compatible with 64 kb/s PCM B-Channels.

Selection of companding curves and digital code

assignment are register programmable. These are

CCITT

G.711

A-law

µ-Law, with true-sign/

Alternate

Digit

Inversion

true-sign/Inverted

Magnitude coding, respectively. Optionally, sign-

magnitude

coding

may

also

selected

for

proprietary applications.

The Filter/CODEC block also implements transmit

and receive audio path gains in the analog domain.

These gains are in addition to the digital gain pad

section and provide an overall path gain resolution of

1.0dB. A programmable gain, voice side-tone path is

also included to provide proportional transmit speech

feedback to the handset receiver. Figure 3 depicts

the nominal half-channel and side-tone gains for the

IDPC.

Intel® and MCS-51® are registered trademarks of Intel Corporation

Motorola® and SPI® are registered trademarks of Motorola Corporation

National® and Microwire® are trademarks of National Semiconductor Corporation

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