MSAN-128 Zarlink Semiconductor, Inc., MSAN-128 Datasheet - Page 10

• Manufacturer Part Number: MSAN-128
• Description: Implementing an ISDN Architecture Using the ST-BUS
• Manufacturer: Zarlink Semiconductor, Inc.

MSAN-128
The
incorporated into it at present because the current
definition of the ISDN Subscriber Access Model
promotes the use of the S reference point in TE’s,
with the U reference point connected to Modem-like
NT equipment and the network.
4.7 Switching
In
equipment, there is a requirement for having circuit
switching capability. The MT8980 and the MT8981
are digital crosspoint switches, based on the ST-BUS
architecture. The MT8980 is a 256 channel by 256
channel non-blocking switch (eight ST-BUS inputs to
eight ST-BUS outputs). This is equivalent to 65536
crosspoints. The MT8981 is a 128 channel by 128
channel non-blocking switch (four ST-BUS inputs to
four ST-BUS outputs, 16384 crosspoints).
The outputs have per channel high impedance
capability, enabling large switching matrices to be
constructed using multiple MT8980/81's.
BUS ports are visible to the microprocessor
interface, to allow control/status information to be
placed
components. The ST-BUS clock signals required are
a frame pulse and a 4096 kHz clock.
4.8 Time Base Generation
Every system needs a common time base as a
timing reference.
must have synchronization between the time bases
of communicating equipment to ensure information is
sampled at the correct time. This synchronization is
performed using phase locked loop techniques: a
locally generated time base, close to the frequency
of a received signal or some derivative of that
frequency, is phase adjusted when the phase
difference between the two signals becomes too
great.
The MT8972 in master mode (Loop termination at
network side) uses an external 10240 kHz clock
source (frequency locked to the ST-BUS clock
signals) to generate timing on the transmit side.
Timing is extracted from the received line signal to
clock in the received data, and the information is
retimed to the ST-BUS timing. Frame pulse and the
4096 kHz clock are input to control the ST-BUS
timing of the component.
In slave mode (Network termination at user side), the
10240 kHz time base is provided by an external
crystal.
received signal, and the phase locked timing is used
A-144
larger
MT8972
on
The time base is phase locked to the
ISDN
ST-BUS
does
systems,
Digital communication systems
not
streams
have
particularly
through
PA/D
The ST-
circuitry
network
these
to generated transmit timing, as well as ST-BUS
timing (frame pulse and 4096 kHz clock) for the rest
of the slave system that the MT8972 resides in.
The MT8930 operates in a very similar manner to the
MT8972 in comparable applications (NT applications
and TE applications), however, the 10240 kHz
external time base of the MT8972 is replaced by an
on-chip voltage controlled oscillator. The ST-BUS
signals are provided externally in NT mode and
sourced by the MT8930 in TE mode.
The thick film hybrid versions of the digital trunk
interfaces
incorporate tunable clock extractors that extract the
data rate from the received data signal.
provides a clock for the line receiver circuit (2048
kHz or 1544 kHz). An 8 kHz signal (nominally the
frequency is dependent on the extracted clock
frequency) is also generated by the digital trunks.
The MT8940 T1/CEPT Digital Phase Locked Loop is
specifically designed to generate an ST-BUS time
base (frame pulse, 4096 kHz and 2048 kHz clock)
and a 1544 kHz clock, using a 12355 kHz Oscillator
input and a 16388 kHz oscillator input.
synchronize a system to the received signal, the
MT8940 can be used to phase lock these timing
signals to the 8 kHz signal extracted from the digital
trunk interface.
5.0 Conclusion
The ST-BUS is a simple inter-component interface
that allows complete connectivity between ISDN
devices. An important aspect of the connectivity is
that it is common to a complete set of ISDN
functions. The flexibility of the ST-BUS architecture,
coupled with the full complement of supporting
components, permits the easy, economical design of
any type of ISDN equipment.
ST-BUS components address the physical layer and
the data link layer needs of ISDN. ST-BUS support
of ISDN shall be extended beyond the current
component family to encompass any new ISDN
recommendations.
makes
interface for ISDN.
ST-BUS
(MH89760,
the
This commitment to support,
preferred
MH89780,
Application Note
inter-component
MH89790)
This
To