MT89L80
Data Sheet
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 MT89L80.
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 MT89L80 as a speech switch and a second
MT89L80 for communication with the line interface circuits.
STo0
STi0
89L80 used
as
speech
switch
MT89L80
D
X
D
R
D
C
STo0
STi0
89L80 used
in message
mode for
control and
signalling
MT8964
Filter/Codec
Signalling
Logic
Line Driver
and
2- to 4-
Wire
Converter
Line Interface Circuit with 8964 Filter/Codec
MT89L80
Figure 7 - Example of Typical Interface between 89L80s and 8964s for Simple Digital Switching
System
Line Interface Circuit
with Codec (e.g. 8964)
8
Speech
Switch
-
89L80
STi0-7
Line 1
8
STo0-7
Controlling
Micro-
Processor
STo0-7
8
STi0-7
•
•
•
Repeated for Lines
2 to 255
•
•
•
Repeated for Lines
2 to 255
8
Control &
Signalling
-
89L80
Line Interface Circuit
with Codec (e.g.8964)
Line 256
Figure 8 - Example Architecture of a Simple Digital Switching System
8
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
