MT8985

2-47

21

24

18

CS

Chip Select (Input). Active low input enabling a microprocessor read or write of

control register or internal memories.

22-29 25-27

29-33

19-21

23-27

D7-D0 Data Bus 7 to 0 (Bidirectional). These pins provide microprocessor access to data

in the internal control register, connect memory high, connect memory low and data

memory.

30

34

28

Ground Rail.

31-38 35-39

41-43

29-33

35-37

STo7-

STo0

ST-BUS Outputs 7 to 0 (Three-state Outputs). Serial data output streams. These

streams are composed of 32 channels at data rates of 2.048 Mbit/s.

39

44

38

ODE Output Drive Enable (Input). This is an output enable for the STo0 to STo7 serial

outputs. If this input is low STo0-7 are high impedance. If this input is high each

channel may still be put into high impedance by software control.

40

1

39

CSTo Control ST-BUS Output (Output). This output is a 2.048 Mb/s line which contains

256 bits per frame. The level of each bit is controlled by the contents of the CSTo bit

in the Connect Memory high locations.

6, 18,

28,

40

12,22

34,

44

NC

No Connection.

Pin Description

Pin #

Name

Description

40

DIP

44

PLCC

44

QFP

Functional Description

With the integration of voice, video and data services

into the same network, there has been an increasing

demand for systems which ensure that data at N x 64

Kbit/s rates maintain frame sequence integrity while

being transported through time slot interchange

circuits. Existing requirements demand time slot

interchange

devices

performing

switching

with

constant

throughput

delay

while

guaranteeing

minimum delay for voice channels.

The MT8985 device provides both functions and

allows existing systems based on the MT8980D to

be easily upgraded to maintain the data integrity

while multiple channel data are transported. The

device is designed to switch 64 kbit/s PCM or N x 64

kbit/s data. The MT8985 can provide both frame

integrity

for

data

applications

and

minimum

throughput switching delay for voice applications on

a per channel basis.

By

using

Mitel

Message

mode

capability,

the

microprocessor can access input and output time

slots on a per channel basis to control devices such

as the MITEL MT8972, ISDN Transceivers and T1/

CEPT trunk interfaces through the ST-BUS interface.

Different digital backplanes can be accepted by the

MT8985 device without user's intervention. The

MT8985 device provides an internal circuit that

automatically identifies the polarity and format of

frame synchronization input signals compatible to

ST-BUS and GCI interfaces.

Device Operation

A functional block diagram of the MT8985 device is

shown in Figure 1. The serial ST-BUS streams

operate continuously at 2.048 Mb/s and are arranged

in 125

µs wide frames each containing 32 8-bit

channels. Eight input (STi0-7) and eight output

(STo0-7) serial streams are provided in the MT8985

device allowing a complete 256 x 256 channel non-

blocking switch matrix to be constructed. The serial

interface clock for the device is 4.096 MHz, as

required in ST-BUS and GCI specifications.

Data Memory

The received serial data is converted to parallel

format by the on-chip serial to parallel converters

and stored sequentially in a 256-position Data

Memory. The sequential addressing of the Data

Memory is generated by an internal counter that is

reset by the input 8 kHz frame pulse (F0i) marking

the frame boundaries of the incoming serial data

streams.

Depending on the type of information to be switched,

the MT8985 device can be programmed to perform