MT9123
Enable Strobe Pin
ENA1
ENB1
ENA2
ENB2
Echo Canceller
A
B
A
B
Port
1
1
2
2
Preliminary Information
Bit Clock (BCLK/C4i)
The BCLK/C4i pin is used to clock the PCM data in
both SSI (BCLK) and ST-BUS (C4i) operations.
In SSI operation, the bit rate is determined by the
BCLK frequency. This input must contain either eight
or sixteen clock cycles within the valid enable strobe
window. BCLK may be any rate between 128 KHz to
4.096 MHz and can be discontinuous outside of the
enable strobe windows defined by ENA1, ENB1,
ENA2 and ENB2 pins. Incoming PCM data (Rin, Sin)
are sampled on the falling edge of BCLK while
outgoing PCM data (Sout, Rout) are clocked out on
the rising edge of BCLK. See Figure 17.
In ST-BUS operation, connect the system C4
(4.096MHz) clock to the C4i pin.
Master Clock (MCLK)
A nominal 20MHz master clock (MCLK) is required
for execution of the MT9123 algorithms. The MCLK
input may be asynchronous with the 8KHz frame. If
only one channel operation is required, (Echo
Canceller A only) the MCLK can be as low as
9.6MHz.
Table 5 - SSI Enable Strobe Pins
PCM Law and Format Control (LAW, FORMAT)
The PCM companding/coding law used by the
MT9123 is controlled through the LAW and FORMAT
pins. ITU-T G.711 companding curves for
µ-Law
and
A-Law are selected by the LAW pin. PCM coding
ITU-T G.711 and Sign-Magnitude are selected by the
FORMAT pin. See Table 6.
Sign-Magnitude
FORMAT=0
ITU-T (G.711)
FORMAT=1
µ-LAW
LAW = 0
1000 0000
1111 1111
0111 1111
0000 0000
A-LAW
LAW =1
1010 1010
1101 0101
0101 0101
0010 1010
PCM Code
µ/A-LAW
LAW = 0 or 1
+ Full Scale
+ Zero
- Zero
- Full Scale
1111 1111
1000 0000
0000 0000
0111 1111
Microport
The serial microport provides access to all MT9123
internal read and write registers and it is enabled
when CONFIG1 and CONFIG2 pins are both set to
logic 0. This microport is compatible with Intel MCS-
51 (mode 0), Motorola SPI (CPOL=0, CPHA=0), and
National Semiconductor Microwire specifications.
The microport consists of a transmit/receive data pin
(DATA1), a receive data pin (DATA2), a chip select
pin (CS) and a synchronous data clock pin (SCLK).
Table 6 - Companded PCM
Linear PCM
The 16-bit 2’s complement PCM linear coding
permits a dynamic range beyond that which is
specified in ITU-T G.711 for companded PCM. The
echo-cancellation algorithm will accept 16 bits 2’s
complement linear code which gives a dynamic
range of +15dBm0.
Linear PCM data must be formatted as 14-bit, 2’s
complement data with three bits of sign extension in
the most significant positions (i.e.: S,S,S,12,11,
...1,0) for a total of 16 bits where “S” is the extended
sign bit. When A-Law is converted to 2’s complement
linear format, it must be scaled up by 6dB (i.e. left
shifted one bit) with a zero inserted into the least
significant bit position. See Figure 8.
The MT9123 automatically adjusts its internal timing
and pin configuration to conform to Intel or Motorola/
National requirements. The microport dynamically
senses the state of the SCLK pin each time CS pin
becomes active (i.e. high to low transition). If SCLK
pin is high during CS activation, then Intel mode 0
timing is assumed. In this case DATA1 pin is defined
as a bi-directional (transmit/receive) serial port and
DATA2 is internally disconnected. If SCLK is low
during CS activation, then Motorola/National timing
is assumed and DATA1 is defined as the data
transmit pin while DATA2 becomes the data receive
pin. The MT9123 supports Motorola half-duplex
processor mode (CPOL=0 and CPHA=0). This
means that during a write to the MT9123, by the
Motorola processor, output data from the DATA1 pin
8-54
MITEL [ MITEL NETWORKS CORPORATION ]
