73K302L

Bell 212A, 103, 202

Single-Chip Modem

April 2000

DESCRIPTION

The 73K302L is a highly integrated single-chip
modem IC which provides the functions needed to
construct a Bell 202, 212A and 103 compatible
modem. The 73K302L is an enhancement of the
73K212L single-chip modem with Bell 202 mode
features added. The 73K302L is capable of 1200 or
0-300 bit/s full-duplex operation over dial-up lines.
4-wire full-duplex capability and a low speed back
channel are also provided in Bell 202 mode. The
73K302L recognizes and generates a 900 Hz soft
carrier turn-off tone, and allows 103 for 300 bit/s
FSK operation. The 73K302L integrates analog,
digital, and switched-capacitor array functions on a
single substrate, offering excellent performance and
a high level of functional integration in a single
28-pin DIP or PLCC package. The 73K302L
operates from a single +5V supply with very low
power consumption.
The 73K302L includes the DPSK and FSK
modulator/demodulator functions, call progress and
handshake tone monitors, test modes, and a tone
generator capable of producing DTMF, answer, and
900 Hz soft carrier turn-off tone. This device
supports Bell 202, 212A and 103 modes of
operation, allowing both synchronous and

(continued)

FEATURES

One-chip Bell 212A, 103 and 202S/T standard
compatible modem data pump

Full-duplex operation at 0-300 bit/s (FSK), 1200 bit/s
(DPSK) or 0-1200 bit/s (FSK) forward channel with or
without 0-150 bit/s back channel

Full-duplex 4-wire operation in Bell 202 mode

Pin and software compatible with other TDK
Semiconductor Corporation K-Series 1-chip
modems

Interfaces directly with standard microprocessors
(8048, 80C51 typical)

Serial port for data transfer

Both synchronous and asynchronous modes of
operation

Call progress, carrier, precise answer tone
(2225 Hz), soft carrier turn-off (SCT), and FSK mark
detectors

DTMF, answer, and SCT tone generators

Test modes available: ALB, DL, RDL, Mark, Space,
Alternating bit patterns

CMOS technology for low power consumption using
60 mW @ 5V from a single power supply

BLOCK DIAGRAM

DIGITAL

PROCESSING

DTMF &

TONE

GENERATORS

FSK

MODULATOR/

DEMODULATOR

PSK

MODULATOR/

DEMODULATOR

SMART

DIALING

DETECT

FUNCTIONS

POWER

TESTS:

ALB, DLB

RDLB

PATTERNS

TRANSMIT

FILTER

DATA

BUS

BUFFER

READ

WRITE

CONTROL

LOGIC

STATUS

AND

CONTROL

LOGIC

8-BIT

BUS

FOR

CONTROL

AND

STATUS

SERIAL

PORT

FOR

DATA

TXA

RXA

I
SET

CLK

CLOCK

GENERATOR

CLK

EXC

ALE

RESET

INT

TXD

RXD

AD0-AD7

RECEIVE

FILTER

73K302L
Bell 212A, 103, 202
Single-Chip Modem

DESCRIPTION

(continued)

asynchronous communications. The 73K302L is
designed to appear to the systems designer as a
microprocessor peripheral, and will easily interface
with popular one-chip microprocessors (80C51
typical) for control of modem functions through its 8-
bit multiplexed address/data bus or via an optional
serial command bus. An ALE control line simplifies
address demultiplexing. Data communications
occurs through a separate serial port only.
The 73K302L is ideal for use in either free standing
or integral system modem products where multi-
standard data communications is desired. Its high
functionality, low power consumption and efficient
packaging simplify design requirements and
increase system reliability. A complete modem
requires only the addition of the phone line interface,
a modem controller, and RS232 level converter for a
typical system.
Tri-mode capability in one-chip allows full-duplex
Bell 212 and 103 operation or assymetrical Bell
202S operation over the 2-wire switched telephone
network. 202T mode full-duplex operation at 1200
bit/s is also possible when operating on 4-wire
leased lines.
A soft carrier turn-off feature facilitates fast line turn
around when using the 202S mode for half-duplex
applications.
The 73K302L is part of TDK Semiconduct K- Series
family of pin and function compatible single-chip
modem products. These devices allow systems to
be configured for higher speeds and Bell or CCITT
operation with only a single component change.

OPERATION

ASYNCHRONOUS MODE
Data transmission for the DPSK mode requires that
data ultimately be transmitted in a synchronous
fashion. The 73K302L includes ASYNC/SYNC and
SYNC/ASYNC converters which delete or insert stop
bits in order to transmit data at a regular rate. In
asynchronous mode the serial data comes from the
TXD pin into the ASYNC/SYNC converter. The
ASYNC/SYNC converter accepts the data provided
on the TXD pin which normally must be 1200 bit/s
+1.0%, 2.5%. The rate converter will then insert or
delete stop bits in order to output a signal which is
1200 bit/s ± .01% (±0.01% is the required
synchronous data rate accuracy).

The SYNC/ASYNC converter also has an extended
overspeed mode which allows selection of an output
overspeed range of either +1% or +2.3%. In the
extended overspeed mode, stop bits are output at
7/8 the normal width.
The serial data stream from the transmit buffer or the
rate converter is passed through the data scrambler
and onto the analog modulator. The data scrambler
can be bypassed under processor control when
unscrambled data must be transmitted. If serial input
data contains a break signal through one character
(including start and stop bits) the break will be
extended to at least 2 times N + 3 bits long (where N
is the number of transmitted bits/character).
Serial data from the demodulator is passed first
through the data descrambler and then through the
SYNC/ASYNC converter. The ASYNC/ASYNC
converter will reinsert any deleted stop bits and
output data at an intra-character rate (bit-to-bit
timing) of no greater than 1219 bit/s. An incoming
break signal (low through two characters) will be
passed through without incorrectly inserting a stop
bit.

SYNCHRONOUS MODE
The Bell 212A standard defines synchronous
operation at 1200 bit/s. Operation is similar to that of
the asynchronous mode except that data must be
synchronized to a provided clock and no variation in
data transfer rate is allowable. Serial input data
appearing at TXD must be valid on the rising edge of
TXCLK.
TXCLK is an internally derived signal in internal
mode and is connected internally to the RXCLK pin
in slave mode. Receive data at the RXD pin is
clocked out on the falling edge of RXCLK. The
ASYNCH/SYNCH converter is bypassed when
synchronous mode is selected and data is
transmitted out at the same rate as it is input.

DPSK MODULATOR/DEMODULATOR
In DPSK mode the 73K302L modulates a serial bit
stream into di-bit pairs that are represented by four
possible phase shifts as prescribed by the Bell 212A
standards. The base-band signal is then filtered to
reduce intersymbol interference on the bandlimited
2-wire telephone line. Transmission occurs using
either a 1200 Hz (originate mode) or 2400 Hz
(answer mode) carrier. Demodulation is the reverse
of the modulation process, with the incoming analog

73K302L

Bell 212A, 103, 202

Single-Chip Modem

signal eventually decoded into di-bits and converted
back to a serial bit stream. The demodulator also
recovers the clock which was encoded into the
analog signal during modulation. Demodulation
occurs using either a 1200 Hz carrier (answer mode
or ALB originate mode) or a 2400 Hz carrier
(originate mode or ALB answer mode). The
73K302L uses a phase locked loop coherent
demodulation technique for optimum receiver
performance.

FSK MODULATOR/DEMODULATOR
The FSK modulator produces a frequency
modulated analog output signal using two discrete
frequencies to represent the binary data. Bell 103
mode uses 1270 and 1070 Hz (originate, mark and
space) or 2225 and 2025 Hz (answer, mark and
space). Bell 202 mode uses 1200 Hz (mark) and
2200 Hz (space for the main channel and 387 Hz
(mark) and 487 Hz (space) for the back channel.
The modulation rate of the back channel is up to 150
baud. Demodulation involves detecting the received
frequencies and decoding them into the appropriate
binary value. The rate converter and
scrambler/descrambler are automatically bypassed
in the 103 or 202 modes.

PASSBAND FILTERS AND EQUALIZERS
High and low band filters are included to shape the
amplitude and phase response of the transmit and
receive signals and provide compromise delay
equalization and rejection of out-of-band signals in
the receive channel. Amplitude and phase
equalization are necessary to compensate for
distortion of the transmission line and to reduce
intersymbol interference in the bandlimited receive
signal. The transmit signal filtering approximates a
75% square root of raised Cosine frequency
response characteristic.

AGC
The automatic gain control maintains a signal level
at the input to the demodulators which is constant to
within 1 dB. It corrects quickly for increases in signal
which would cause clipping and provides a total
receiver dynamic range of >45 dB.

PARALLEL BUS INTERFACE
Four 8-bit registers are provided for control, option
select and status monitoring. These registers are

addressed with the AD0, AD1, and AD2 multiplexed
address lines (latched by ALE) and appear to a
control microprocessor as four consecutive memory
locations. Two control registers and the tone register
are read/write memory. The detect register is read
only and cannot be modified except by modem
response to monitored parameters.

SERIAL COMMAND INTERFACE MODE
The serial command interface allows access to the
73K302L control and status registers via a serial
command port. In this mode the AD0, AD1 and AD2
lines provide register addresses for data passed
through the data pin under control of the

RD and

WR lines. A read operation is initiated when the RD
line is taken low. The first bit is available after

RD is

brought low and the next seven cycles of EXCLK will
then transfer out seven bits of the selected address
location LSB first. A write takes place by shifting in
eight bits of data LSB first for eight consecutive
cycles of EXCLK.

WR is then pulsed low and data

transfer into the selected register occurs on the
rising edge of

WR.

SPECIAL DETECT CIRCUITRY
The special detect circuitry monitors the received
analog signal to determine status or presence of
carrier, answer tone and weak received signal (long
loop condition), special tones such as FSK marking
and the 900 Hz soft carrier turn-off tone are also
detected. A highly frequency selective call progress
detector provides adequate discrimination to
accurately detect lower quality call progress signals.

DTMF GENERATOR
The DTMF generator will output one of 16 standard
tone pairs determined by a 4-bit binary value and TX
DTMF mode bit previously loaded into the tone
register. Tone generation is initiated when the DTMF
mode is selected using the tone register and the
transmit enable (CR0 bit D1) is changed from 0 to 1.

SOFT CARRIER TURN-OFF TONE GENERATOR
The soft carrier turn-off tone generator will output a
900 Hz tone. When activated in Bell 202 main
channel transmit mode, the output signal will shift to
900 Hz, maintaining phase continuity during the
transition.

73K302L
Bell 212A, 103, 202
Single-Chip Modem

PIN DESCRIPTION

POWER

NAME

PLCC/PIN

DIP NUMBER

TYPE

DESCRIPTION

GND

System Ground.

VDD

Power supply input, 5V ±10%. Bypass with 0.1 and 22 µF capacitors
to GND.

VREF

An internally generated reference voltage. Bypass with 0.1 µF
capacitor to GND.

ISET

Chip current reference. Sets bias current for op-amps. The chip
current is set by connecting this pin to VDD through a 2 M

resistor.

ISET should be bypassed to GND with a 0.1 µF capacitor.

PARALLEL MICROPROCESSOR INTERFACE

ALE

Address latch enable. The falling edge of ALE latches the address on
AD0-AD2 and the chip select on

CS.

AD0-AD7

4-11

I/O

Address/data bus. These bidirectional tri-state multi-plexed lines carry
information to and from the internal registers.

Chip select. A low on this pin during the falling edge of ALE allows a
read cycle or a write cycle to occur. AD0-AD7 will not be driven and
no registers will be written if

CS (latched) is not active. The state of

CS is latched on the falling edge of ALE.

CLK

Output clock. This pin is selectable under processor control to be
either the crystal frequency (for use as a processor clock) or 16 times
the data rate for use as a baud rate clock in DPSK mode only. The
pin defaults to the crystal frequency on reset.

INT

Interrupt. This open drain output signal is used to inform the
processor that a detect flag has occurred. The processor must then
read the detect register to determine which detect triggered the
interrupt.

INT will stay low until the processor reads the detect register

or does a full reset.

Read. A low requests a read of the 73K302L internal registers. Data
cannot be output unless both

RD and the latched CS are active or low.

RESET

Reset. An active high signal on this pin will put the chip into an inactive
state. All control register bits (CR0, CR1, Tone) will be reset. The
output of the CLK pin will be set to the crystal frequency. An internal
pull down resistor permits power on reset using a capacitor to VDD.

73K302L

Bell 212A, 103, 202

Single-Chip Modem

PARALLEL MICROPROCESSOR INTERFACE

(continued)

NAME

PLCC/PIN

DIP NUMBER

TYPE

DESCRIPTION

Write. A low on this informs the 73K302L that data is available on
AD0-AD7 for writing into an internal register. Data is latched on the
rising edge of

WR. No data is written unless both WR and the latched

CS are active low.

SERIAL MICROPROCESSOR INTERFACE

A0-A2

DATA

I/O

Serial Control Data. Data for a read/write operation is clocked in or
out on the falling edge of the EXCLK pin. The direction of data flow is
controlled by the

RD pin. RD low outputs data. RD high inputs data.

Read. A low on this input informs the 73K302L that data or status
information is being read by the processor. The falling edge of the

signal will initiate a read from the addressed register. The

RD signal

must continue for eight falling edges of EXCLK in order to read all
eight bits of the referenced register. Read data is provided LSB first.
Data will not be output unless the

RD signal is active.

Write. A low on this input informs the 73K302L that data or status
information has been shifted in through the DATA pin and is available
for writing to an internal register. The normal procedure for a write is
to shift in data LSB first on the DATA pin for eight consecutive falling
edges of EXCLK and then to pulse

WR low. Data is written on the

rising edge of

WR.

Note:

The serial control mode is provided by tying ALE high and

CS low. In this configuration AD7 becomes the

data input and AD0, AD1 and AD2 become the address only. See the SERIAL CONTROL TIMING
diagram on page22

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