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MT8980D

ISO-CMOS ST-BUS FAMILY Digital Switch

Zarlink Semiconductor Inc 

MT8980D

Data Sheet

Applications

Use in a Simple Digital Switching System

Figs. 7 and 8 show how MT8980s can be used with MT8964s to form a simple digital switching system. Fig. 7

shows the interface between the MT8980s and the filter/codecs. Fig. 8 shows the position of these components in

an example architecture.

The MT8964 filter/codec in Fig. 7 receives and transmits digitized voice signals on the ST-BUS input DR, and ST-

BUS output DX, respectively. These signals are routed to the ST-BUS inputs and outputs on the top MT8980, which

is used as a digital speech switch.

The MT8964 is controlled by the ST-BUS input DC originating from the bottom MT8980, which generates the

appropriate signals from an output channel in Message Mode. This architecture optimizes the messaging capability

of the line circuit by building signalling logic, e.g., for on-off hook detection, which communicates on an ST-BUS

output. This signalling ST-BUS output is monitored by a microprocessor (not shown) through an ST-BUS input on

the bottom MT8980.

Fig. 8 shows how a simple digital switching system may be designed using the ST-BUS architecture. This is a

private telephone network with 256 extensions which uses a single MT8980 as a speech switch and a second

MT8980 for communication with the line interface circuits.

A larger digital switching system may be designed by cascading a number of MT8980s. Fig. 9 shows how four

MT8980s may be arranged in a non-blocking configuration which can switch any channel on any of the ST-BUS

inputs to any channel on the ST-BUS outputs.

8980 used

as

speech

switch

STo0

STi0

MT8980

8980 used

in message

mode for

control and

signalling

STo0

STi0

MT8980

DX

DR

MT8964

Filter/Codec

DC

Signalling

Logic

Line Driver

and

2- to 4-

Wire

Converter

Line Interface Circuit with 8964 Filter/Codec

Figure 7 - Example of Typical Interface between 8980s and 8964s for Simple Digital Switching

System

8

Zarlink Semiconductor Inc.

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