MT8972B datasheet(4/20 Pages) MITEL

Part #	MT8972B

Description	ISO2-CMOS ST-BUS??FAMILY Digital Subscriber Interface Circuit Digital Network Interface Circuit

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Manufacturer	MITEL [Mitel Networks Corporation]

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MT8971B/72B

9-110

Functional Description

The MT8971B/72B is a device which has been

designed primarily as an interface for the Integrated

Services Digital Network (ISDN). However, it may be

used in practically any application that requires high

speed data transmission over two wires, including

smart telephone sets, workstations, data terminals

and computers.

In the ISDN, the DNIC is ideal for providing the

interface at the U reference point. The device

supports the 2B+D channel format (two 64 kbit/s B-

channels and one 16 kbit/s D-channel) over two

wires as recommended by the CCITT. The line data

is converted to and from the ST-BUS format on the

system side of the network to allow for easy

interfacing with other components such as the S-

interface device in an NT1 arrangement, or to digital

PABX components.

Smart telephone sets with data and voice capability

can be easily implemented using the MT8971B/72B

as a line interface. The device’s high bandwidth and

long loop length capability allows its use in a wide

variety of sets.

This can be extended to provide full

data and voice capability to the private subscriber by

the installation of equipment in both the home and

central office or remote concentration equipment.

Within the subscriber equipment the MT8971B/72B

would terminate the line and encode/ decode the

data and voice for transmission while additional

electronics could provide interfaces for a standard

telephone

set and any

number of data ports

supporting standard data rates for such things as

computer communications and telemetry for remote

meter reading. Digital workstations with a high

degree of networking capability can be designed

using the DNIC for the line interface, offering up to

160 kbit/s data transmission over existing telephone

lines. The MT8971B/72B could also be valuable

within existing computer networks for connecting a

large number of terminals to a computer or for

intercomputer links. The highest data rates existing

for terminal to computer links is 19.2 kbit/s over

conventional analog modems. With the DNIC, this

can be increased up to 160 kbit/s at a very low cost

per line for terminal to computer links and in many

cases

this

bandwidth

would

be

sufficient

for

computer to computer links.

Figure 1 shows the block diagram of the MT8971B/

72B. The DNIC provides a bidirectional interface

between the DV (data/voice) port and a full duplex

line operating at 80 or 160 kbit/s over a single pair of

twisted wires. The DNIC has three serial ports. The

DV port (DSTi/Di, DSTo/Do), the CD (control/data)

port (CDSTi/CDi, CDSTo/CDo) and a line port (LIN,

LOUT). The data on the line is made up of information

from the DV and CD ports. The DNIC must combine

information received from both the DV and CD ports

and put it onto the line. At the same time, the data

received from the line must be split into the various

channels and directed to the proper ports. The

usable data rates are 72 and 144 kbit/s as required

for the basic rate interface in ISDN. Full duplex

transmission is made possible through on board

adaptive echo cancellation.

The DNIC has various modes of operation which are

selected through the mode select pins MS0-2. The

two major modes of operation are the MODEM

(MOD) and DIGITAL NETWORK (DN) modes. MOD

mode is a transparent 80 or 160 kbit/s modem.

In

DN mode the line carries the B and D channels

formatted for the ISDN at either 80 or 160 kbit/s. In

the DN mode the DV and CD ports are standard ST-

BUS and in MOD mode they are transparent serial

data streams at 80 or 160 kbit/s. Other modes

include: MASTER (MAS) or SLAVE (SLV) mode,

where the timebase and frame synchronization are

provided externally or are extracted from the line and

DUAL or SINGLE (SINGL) port modes, where both

the DV and CD ports are active or where the CD port

is inactive and all information is passed through the

DV port. For a detailed description of the modes see

“Operating Modes” section.

In DIGITAL NETWORK (DN) mode there are three

channels transferred by the DV and CD ports. They

are the B, C and D channels. The B1 and B2

channels each have a bandwidth of 64 kbit/s and are

used for carrying PCM encoded voice or data. These

channels

are

always

transmitted

and

received

through the DV port (Figures 3, 4, 5, 6). The C-

channel, having a bandwidth of 64 kbit/s, provides a

means for the system to control the DNIC and for the

DNIC to pass status information back to the system.

The C-channel has a Housekeeping (HK) bit which is

the only bit of the C-channel transmitted and

received on the line. The 2B+D channel bits and the

HK bit are double-buffered. The D-channel can be

transmitted or received on the line with either an 8,

16 or 64 kbit/s bandwidth depending on the DNIC’s

mode of operation. Both the HK bit and the D-

channel can be used for end-to-end signalling or low

speed data transfer. In DUAL port mode the C and D

channels are accessed via the CD port (Figure 7)

while in SINGL port mode they are transferred

through the DV port (Figures 5, 6) along with the B1

and B2 channels.

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