73K222AL
V.22, V.21, Bell 212A, 103
Single-Chip
long (where N is the number of transmitted
bits/character).
DESCRIPTION (continued)
This device supports V.22 (except mode v) and V. 21
modes of operation, allowing both synchronous and
asynchronous communications. Test features such as
analog loop, digital loop, and remote digital loopback are
supported. Internal pattern generators are also included for
self-testing. The 73K222AL 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-
Serial data from the demodulator is passed first
through the data descrambler and then through
the SYNC/ASYNC converter. The SYNC/ASYNC
convertor will reinsert any deleted stop bits and
transmit 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.
bit multiplexed address/data bus or serial control bus. An
ALE control line simplifies address demultiplexing. Data
communications occurs through a separate serial port only.
The SYNC/ASYNC converter also has an
extended overspeed mode which allows selection
of an overspeed range of either +1% or +2.3%. In
The 73K222AL is ideal for use in either free standing or
integral system modem products where full-duplex 1200
bit/s data communications over the 2-wire switched
telephone network 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 control microprocessor, and RS-232 level
converter for a typical system. The 73K222AL is part of
TDK Semiconductor Corporation's 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.
the extended overspeed mode, stop bits are
output at 7/8 the normal width.
SYNCHRONOUS MODE
The CCITT V.22 standard defines synchronous
operation at 600 and 1200 bit/s. The Bell 212A
standard defines synchronous operation only 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
OPERATION
ASYNCHRONOUS MODE
Data transmission for the DPSK mode requires that data
ultimately be transmitted in a synchronous fashion. The
73K222AL includes ASYNC/SYNC and SYNC/ASYNC
converters which delete or insert stop bits in order to
transmit data within a ±0.01% 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 or 600 bit/s +1.0%, -2.5%. The converter will
then insert or delete stop bits in order to output a signal
which is 1200 or 600 bit/s ± 0.01% (± 0.01% is required
synchronous data rate accuracy).
selected and data is transmitted out at the same rate
as it is input.
DPSK MODULATOR/DEMODULATOR
The 73K222AL modulates a serial bit stream into
di-bit pairs that are represented by four possible
phase shifts as prescribed by the Bell 212A or
V.22 standards. The baseband 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 carrier (answer mode). Demodulation is
the reverse of the modulation process, with the
incoming analog 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
The serial data stream from the ASYNC/SYNC
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. The ASYNC/SYNC
converter and the data scrambler are bypassed in all
FSK modes. 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
2
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