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MT9123AP

Dual Voice Echo Canceller

Mitel Networks 

Preliminary Information

MT9123

CONFIG1

CONFIG2

CONFIGURATION

0

0

(selects Controller Mode)

0

1

Extended Delay Mode

1

0

Back-to-Back Mode

1

1

Normal Mode

Table 3 - Configuration in Controllerless Mode

Controller Mode

In Control Register 1, the Normal configuration can

be programmed by setting both BBM and Extended-

Delay bits to 0. Back-to-Back configuration can be

programmed by setting the BBM bit to 1 and

Extended-Delay bit to 0. Extended-Delay

configuration can be programmed by setting the

Extended-Delay bit to 1 and BBM bit to 0. Both BBM

and Extended-Delay bits in Control Register 1 can

not be set to 1 at the same time.

PCM Data I/O

The PCM data transfer for the MT9123 is provided

through two PCM ports. PORT1 consists of Rin and

Sout pins while PORT2 consists of Sin and Rout Pins.

The Data is transferred through these ports

according to either ST-BUS or SSI conventions. The

device determines the mode of operation by

monitoring the signal applied to the F0i pin. When a

valid ST-BUS frame pulse is applied to the F0i pin,

the MT9123 will assume ST-BUS operation. If F0i is

tied continuously to Vss the MT9123 will assume SSI

operation.

ST-BUS Operation

The ST-BUS PCM interface conforms to Mitel’s ST-

BUS standard and it is used to transport 8 bit

companded PCM data (using one timeslot) or 16 bit

2’s complement linear PCM data (using two

timeslots). Pins ENA1 and ENB1 select timeslots on

PORT1 while pins ENA2 and ENB2 select timeslots

on PORT2. See Table 4 and Figures 5 to 8.

PORT1

Rin/Sout

Enable Pins

ST-BUS Mode

Selection

PORT2

Sin/Rout

Enable Pins

ENB1 ENA1

ENB2 ENA2

0 0 Mode 1. 8 bit companded PCM I/O on 0

0

timeslots 0 & 1.

0 1 Mode 2. 8 bit companded PCM I/O on 0

1

timeslots 2 & 3.

1 0 Mode 3. 8 bit companded PCM I/O on 1

0

timeslots 2 & 3. Includes D & C chan-

nel bypass in timeslots 0 & 1.

1 1 Mode 4. 16 bit 2’s complement linear 1

1

PCM I/O on timeslots 0 - 3.

Table 4 - ST-BUS Mode Select

Note that if the device is in back-to-back or extended

delay configurations, the second timeslot in any ST-

BUS Mode contains undefined data. This means that

the following timeslots contain undefined data:

timeslot 1 in ST-BUS Mode 1; timeslot 3 in ST-BUS

Modes 2 & 3 and timeslots 2 and 3 in ST-BUS Mode

4.

SSI Operation

The SSI PCM interface consists of data input pins

(Rin, Sin), data output pins (Sout, Rout), a variable

rate bit clock (BCLK), and four enable pins

(ENA1,ENB1, ENA2 and ENB2) to provide strobes

for data transfers. The active high enable may be

either 8 or 16 BCLK cycles in duration. Automatic

detection of the data type (8 bit companded or 16 bit

2’s complement linear) is accomplished internally.

The data type cannot change dynamically from one

frame to the next.

In SSI operation, the frame boundary is determined

by the rising edge of the ENA1 enable strobe (see

Figure 9). The other enable strobes (ENB1, ENA2

and ENB2) are used for parsing input/output data

and they must pulse within 125 microseconds of the

rising edge of ENA1. If they are unused, they must

be tied to Vss.

In SSI operation, the enable strobes may be a mixed

combination of 8 or 16 BCLK cycles allowing the

flexibility to mix 2’s complement linear data on one

port (e.g., Rin/Sout) with companded data on the

other port (e.g., Sin/Rout).

8-53

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