MT8930CE datasheet(6/42 Pages) MITEL

6 / 42 page

MT8930C

9-38

Figure 4 - ST-BUS Channel Assignment

Intel microprocessor bus signals and timing.

The

SNIC also has provisions for a controllerless mode

(Cmode=0),

where

the

microprocessor

port

redeﬁned to allow access to the control/status

registers via external hardware.

The three major blocks of the MT8930C, consisting

of the system serial interface (ST-BUS), HDLC

transceiver, and the digital subscriber loop interface

(S-interface) are interconnected by high speed data

busses.

Data sent to and received from the

S-interface port (B1, B2 and D channels) can be

accessed from either the parallel microprocessor

port or the serial ST-BUS port. This is also true for

SNIC control and status information (C-channel).

Depacketized D-channel information to and from the

HDLC section can only be accessed through the

parallel microprocessor port.

S-Bus Interface

The S-Bus is a four wire, full duplex, time division

multiplexed transmission facility which exchanges

information at 192 kbit/s rate including two 64 kbit/s

PCM voice or data channels, a 16 kbit/s signalling

channel and 48 kbit/s for synchronization and

overhead.

The relative position of these channels

with respect to the ST-BUS is shown in Figures 4

and 5.

The SNIC makes use of the ﬁrst four channels on the

ST-BUS to transmit and receive control/status and

data to and from the S-interface port. These are the

B, D and C-channels (see Figure 4).

The B1 and B2 channels each have a bandwidth of

64 kbit/s and are used to carry PCM voice or data

across the network.

The

D-channel

primarily

intended

carry

signalling information for circuit switching through the

ISDN network. The SNIC provides the capability of

having a 16 kbit/s or full 64 kbit/s D-channel by

allocating the B1-channel timeslot to the D-channel.

Access to the depacketized D-channel is only

granted through the parallel microprocessor port.

The C-channel provides a means for the system to

control and monitor the functionality of the SNIC.

This control/status channel is accessed by the

system through the ST-BUS or microprocessor

port.

The C-channel provides access to two

registers which provide complete control over the

state activation machine, the D-channel priority

mechanism as well as the various maintenance

functions. A detailed description of these registers is

discussed in the microprocessor port interface.

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