MT8982AC datasheet(3/14 Pages) MITEL

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ISO-CMOS

MT8982

2-33

Functional Description

The MT8982 (MiniDX) provides cost effective time

switching

capability

for

small

size

applications

utilizing up to two serial Time Division Multiplexed

(TDM) streams. Each TDM stream consists of 32 64

kb/s channels, giving the MiniDX a maximum

capacity of 64 channels.

The input framing signal

may be either a ST-BUS or a GCI frame pulse. The

MT8982 will output a delayed or advanced frame

pulse in the opposite format to permit conversion

between the two formats.

The MiniDX can switch data from any channel in one

of the two serial input TDM streams to any channel in

either of the two serial output TDM streams.

The

microcontroller controlling the MiniDX writes to the

MT8982

Connect

Memory

establish

the

connection between the required input TDM channel

and the selected output TDM channel(s). By reading

the Connect Memory the microcontroller can check

switched connections which have already been

established.

The MiniDX can also operate in message mode

where the microcontroller transmits the data on the

TDM serial stream. The microcontroller writes to the

MT8982 Connect Memory to transmit data on the

required output TDM channels.

Reading the Data

Memory of the MT8982 allows the microcontroller to

receive messages from TDM input channels. These

operations are useful for control of other ST-BUS

components or for interprocessor communication.

Hardware Description

TDM Interface

The MT8982 continuously receives TDM serial data

at 2048 kbit/s through two serial inputs. These serial

streams are then converted into a parallel format and

stored sequentially in a 64x8 bit Data Memory. The

sequential addressing is generated by an internal

counter that is reset by the input 8 kHz frame pulse

(F0i) which marks the frame boundaries of the

incoming serial data stream. This counter increments

with each timeslot so that it matches the binary count

of the timeslot of the incoming data.

The TDM

timeslot count always corresponds to the ST-BUS

channel positions. An extra address bit is used to

differentiate between the two input data streams.

The input 8 kHz frame pulse may be either ST-BUS

or GCI formatted. A ST-BUS formatted frame pulse

is an active low signal which straddles the frame

boundary. It idles high the rest of the time. A GCI

formatted frame pulse is active high at the beginning

of timeslot 5 (relative to the MT8982) and idles low.

The MT8982 automatically determines the type of

frame pulse from the level of the idle over ﬁve clock

periods. A ST-BUS formatted frame pulse resets the

internal address counters to zero. A GCI formatted

frame pulse resets the counters to ﬁve.

F0o outputs a frame pulse in the opposite format. If

F0i is a ST-BUS formatted frame pulse, F0o will be a

GCI formatted frame pulse delayed by ﬁve channels

after F0i. If F0i is a GCI formatted frame pulse, F0o

will be a ST-BUS formatted frame pulse delayed by

27 channels (32-5).

During normal operation every second falling edge of

the clock marks a timeslot boundary and the input

data is clocked in by the rising edge, three-quarters

of the way into the bit cell.

The master clock must

be 4.096 MHz for the F0o signal to be valid and to

receive a GCI formatted F0i.

Data which is output onto a TDM serial output

channel may come from two sources; the Data

Memory or the Connect Memory.

If a channel is

conﬁgured in connection mode, the source of output

data is the Data Memory. If a channel is conﬁgured

in message mode, the source of the output data is

the Connect Memory. Data destined for a particular

channel on the serial output links is read from the

data or connect memory in the previous channel

timeslot. This allows for delay in RAM access and

parallel-to-serial conversion.

Each output data

channel can also be placed in tristate mode.

When an output channel is in connection mode, the

TDM output data is read from a Data Memory

location pointed to by an address stored in the 64x8

bit

Connect

Memory.

The

Connect

Memory

locations are addressed sequentially, with each

location corresponding to an output TDM link/

channel. In the channel time before the data is to be

output, the contents of each Connect Memory

location are output to the address bus of the Data

Memory. The contents of the Data Memory at the

selected address are then transferred to the parallel-

to-serial converter.

The parallel-to-serial converter

outputs onto the TDM serial stream during the

correct channel time. By having the output channel

specify the input channel, the user can route the

same input channel to several output channels. This

function is useful for broadcasting or resource

channel uses.

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