Advance Information
1.0
Functional Description
MT90812
The functional block diagram of Fig. 1 depicts the main operations performed by the MT90812. The integrated
digital switch has three TDM streams. The two local TDM serial streams, STi/o0 and STi/o1, operate at
2048kbit/s and are arranged in 125us wide frames each containing 32 8-bit channels. The third TDM stream,
comprised of EST0 and EST1 can be used as an additional serial stream at 2.048, 4.096 or 8.192 Mb/s,
supporting 32, 64 or 128 channels, respectively.
The expansion bus, EST0/1 operates in two modes, TDM Link and IDX Link modes. IDX Link mode allows
multiple MT90812 devices to be linked together very efficiently. In IDX Link mode, the incoming data on the
local TDM streams of each MT90812 is transferred onto the expansion bus to enable switching channels
between a maximum of four MT90812 devices. For TDM Link mode, the expansion bus is configured as a TDM
serial stream which can run at 2.048, 4.096 or 8.192 Mb/s. In TDM Link mode, the MT90812 can be connected
to more peripheral devices or to other digital switches (i.e. MT8980/1/2 or MT8985/6) to support larger matrices
of MT90812 devices.
The MT90812 can switch data from channels on the local and expansion input streams to channels on the local
and expansion output streams. The controlling microprocessor can simultaneously read channels on TDM
inputs or write to channels on TDM outputs (Message Mode). To the microprocessor, the MT90812 looks like a
memory peripheral. The microprocessor can write to the MT90812 to establish switched connections between
input TDM channels and output TDM channels, or to transmit messages on output TDM channels. By reading
from the MT90812, the microprocessor can receive messages from TDM input channels or check which
switched connections have already been established.
The MT90812 provides conference call capability and supports a total of 15 parties, distributed over a
maximum of 5 conferences. (i.e. 1x15 parties, 3x5 parties, 5x3 parties etc.). Conference parties can be from
any of the incoming channels on the local or expansion TDM streams.
Gain Control is provided on the outgoing channels, with a range of +3 to -27 dB in steps of 1dB, as well as -
∞
dB. If a channel is in a conference, incoming and/or outgoing gain control is provided. Conference incoming
gain also ranges from +3 to -27 dB in steps of 1dB, as well as -
∞
dB. Conference outgoing gain can range from
0 to -9 dB in steps of 3 dB.
A tone source of 32 dual tones is generated from the tone generator block and stored in Data Memory.
Outgoing gain control of +3 to -27 dB in steps of 1dB, as well as -
∞
dB, is provided for each tone. Seven of the
thirty-two tones are programmable in frequency. The 32 locations can be switched to outgoing channels or
accessed by the microprocessor.
A phase coherent FSK transmitter generates two output frequencies, representing the ‘marks’ and ‘spaces’,
selectable to Bell 202 or CCITT V.23 standards at 1200 baud. The FSK transmitter output is a PCM coded
signal that can be directed to any outgoing local TDM channel.
Two energy detect blocks provide monitoring capability of supervisory signalling for any of the TDM channels.
D-Channel access is provided to link the microprocessor to the transceivers. There are two modes of message
formats that can be selected. The D-Channel Basic Receive Transmit (DBRT) mode provides basic formatting
of the data, which includes start and stop signalling and parity checking. In DBRT mode there are RX and TX
buffers, 32 bytes in length, which can be allocated to any of the incoming/outgoing channels of the TDM
streams. The HDLC mode provides a control interface to facilitate the multiplexing of an external HDLC
controller (MT8952) over any of the local TDM streams’ D-Channels.
C-Channel access for control of ST-BUS family of devices (e.g. MT9160B, MT9171/72, MT8930, MT8910) is
provided through Message Mode.
Each of the programmable parameters within the functional blocks are accessed through a parallel
microprocessor port compatible with CPU non-multiplexed bus and Intel®, Motorola® and National®
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MITEL [ MITEL NETWORKS CORPORATION ]
