MT9171/72

Data Sheet

5

Zarlink Semiconductor Inc.

Functional Description

The MT9171/72 is a device which 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. 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 MT9171/72 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

MT9171/72 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 MT9171/72 could also be valuable

within existing computer networks for connecting a large number of terminals to a computer or for intercomputer

links. With the DNIC, this can be accomplished at 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 MT9171/72. 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

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.