HIGH SPEED FAMILY OF ULTRA SMALL MODEMS
CH2056A /-B / ET-B
–
V.92 / 57,600bps / TBR21
CH1799A /-B / ET-B
–
V.34bis / 33,600bps / TBR21
CH1794A /-B / ET-B
–
V.32bis / 14,400bps / TBR21
FEATURES
INTRODUCTION
Supports V.92, V.90, V.34bis, V.34, V.32bis, V.23,
The CH2056A, CH1799A and CH1794A (HS Modem
V.32, V.22bis, V.22A/B, V.23, V.21, Bell 212A and
Family) are industrial grade high-speed modem
103.
modules. Each HS Modem product supports a range
CH2056A supports V.80 Synchronous operation.
of modem standards and speeds from 300bps to
14,400bps, 28,800bps, 33,600bps or 57,600bps. By
Error correcting: V.42 LAPM, MNP 2-4 and
using built in compression algorithms the operation
MNP10. MNP10 Data through put enhancement
speed can be expanded to the maximum DTE rate of
for cellular operation.
57.6kbps for the CH1794A, 115.2kbps for the
Data Compression: V.42bis, V.44, and MNP 5
CH1799A and 230.4kbps for the CH2056A. A choice
of error correcting schemes is available including MNP
DTE serial interface with speeds up to 230.4kbps
10 for cellular telephone applications. The HS Modem
(CH2056A),
115.2
(CH1799A)
or
57.6kbps
family supports Send and Receive FAX.
The
(CH1794A).
CH179XA-L/CH2056A-L
and
CH179XAR-
RoHS Compliant versions available.
L/CH2056AR-L operates exclusively on non-voltage
Low Power 3.3V operation: 170mW (nominal).
bearing leased line.
5V operation: 300mW (nominal).
The HS Modem family is pin compatible with
Automatic baud rate adaptability utilizing speed
Cermetek’s low cost CH1786A V.22bis, 2400bps
sensing, flow control and data buffers.
modem family. Each module in the HS Modem family
is a self-contained modem and is FCC Part 68
DTMF Encoding and Decoding.
approved (pending) and Industry Canada approved
Send & Receive FAX class 1, Group 3 supported.
(pending).
Additionally, the CH179XA/CH2056A-
Serial V.24 interface: 5V tolerant.
B/ET-B
and
the
CH1799AR/CH2056AR-B/ET-B
products meet the European TBR21 requirements.
NVRAM directory and stored profiles.
AT Command structure, with extensions.
These ultra small modules are designed for PCB
Built-in DAA with 1500 VAC RMS isolation 2122V
through-hole mounting and are 1.01” x 1.27” x 0.52”
peak surge protection.
(nominal) in size. The HS Modem family requires only
two external interfaces: a ITU-T V.24 serial interface
UL 60950 and CSA C22.2 950 Recognized
for direct access to a UART, and a Tip and Ring RJ-
(E251266) (pending).
11C Jack for the PSTN line connection.
The HS
FCC Part 68 approved (pending):
Modem can be controlled with industry standard AT
commands and is compatible with available industry
US:B46MM07BCHXXXXAYY.
communication software.
Industry
Canada
CS-03
Part
I
Registered
(pending):
IC:176A-CHXXXXAY.
DESCRIPTION OF FUNCTIONAL BLOCKS
AND DISCUSSION OF BASIC OPERATIONS
PCM upstream (V.92 only).
Figure 1 contains a functional block drawing of the HS
Modem-on-Hold (V.92 only).
Modem family of products. Each HS Modem product
Quick Connect (V.92 only).
consists
of
a
serial
interface
buffer,
modulator/demodulator, modem controller with error
Size: 1.01” x 1.27” x 0.52” (nominal).
correction and data compression, non-volatile RAM
Pin compatible with low speed CH1786A.
and a DAA.
Fast Connect (V.22).
Serial Host Interface Buffer. The HS Modem utilizes
Caller ID (optional).
a serial V.24 EIA 232-E 5V interface to control the
Zero Power (optional).
modem. The HS Modem products can communicate
over the serial interface with the Data Terminal
Off-Hook Indication (optional).
Equipment (DTE) at a fixed speed regardless of the
Leased Line version available.
carrier line modulation speed (DCE) of the PSTN
modem connection. This eliminates the need to have
TBR21 Compliant version available.
2007 Cermetek Microelectronics, Inc.
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Document No. 607-0020 Revision B (01/07)
Cermetek Microelectronics, Inc.
CH179XA/2056A High Speed Family of Ultra Small Modems
the DTE step up or step down in speed based on the
The HS Modem family is designed to meet North
in-coming or out-going PSTN communication data
American telephone standards as set by the FCC Part
rate. Hence, the DTE can train the CH2056A, to say
68 (USA) and CSA CS-03 Part I (Canada). Among the
56kbps, and talk to a slower in-coming data
more critical parameters, the PSTN line interface is
connection at say, 2400bps without changing host
designed to meet 1500 VAC RMS isolation and
speed. Conversely, the host DTE trained at 14.4kbps
provide 2122V peak surge protection. Consequently,
can also communicate with the modems at higher
the HS Modem family of products satisfies U.S. and
speeds, say 28.8kbps.
This is accomplished by
Canadian
requirements,
and
will
meet
other
invoking internal automatic data flow control. The HS
international
approval
agency
requirements
that
Modem family has a resident buffer to allow for this
specify these levels of isolation.
auto baud operation.
Pins 1 and 2 function as both input and output
connections to the PSTN. To maximize field reliability
in hostile environments, for Canadian approval, for UL
compliance, and also optionally for FCC Part 15
compliance, these two pins must be routed through an
external network such as that briefly described in
Figure 6A and described in more detail in Cermetek
Application Note # 126.
Each HS Modem product comes with FCC Part 68
approval and is shipped from the factory with an FCC
Label indicating registration number and ringer
equivalent. This label should be prominently displayed
on the end product. Canadian approval for CH1799A
is listed on page 1.
Canadian approvals for other
products in Cermetek’s High Speed Modem Family are
available upon request. With the exception of the U.S.
Figure 1. Functional Block Diagram of HS Modem
and Canada, most countries require submission of the
Family.
final product or system containing the HS Modem to
the appropriate governing regulatory agency for
Non-Volatile RAM (NVRAM).
NVRAM can store
approval. Typically this is accomplished by submitting
user-customized
configurations.
The
AT&Wn
the final end product to an independent test house or
command will store the active modem configuration in
consultant for evaluation. The test house/consultant
one of two NVRAM locations as selected by an n of 0
then
forwards
the
test
results
and
applicable
or 1. The AT&Yn command selects one of the stored
documents to the regulatory agency.
Contact
modem configurations to be automatically recalled and
Cermetek for a list of suggested consultants.
made active upon reset or power up.
The ATZn
command immediately recalls and activates a stored
Modulation/Demodulation/Error
Correcting
and
configuration. See Table 6 for storable S-Registers
Data Compression. These functions are provided by
and Commands.
an industry standard modem chip set which has been
adapted for use with the HS Modem family.
The
The NVRAM can save up to four telephone numbers,
Modulation/Demodulation
scheme
supports
line
with up to 31 digits or modifiers in each telephone
equalization, forward error correction and the industry
number.
The AT&Zn=s command will store s, the
modem standards listed below.
telephone number dial string. The ATDS=n command
will cause the modem to dial one of the four stored
telephone numbers. The NVRAM storage location for
SUPPORTED MODULATION STANDARDS
the four telephone numbers is selected by an n of 0, 1,
Bell 103
ITU-T V.22
2, or 3.
Bell212A
ITU-T V.22bis
ITU-T V.32
Telephone Line Interface or DAA. High performance
ITU-T V.32bis
modems are extremely sensitive to DAA (Data Access
ITU-T V.34
Arrangement) performance. The difference between a
ITU-T V.34bis
good modem and a fair one is in the DAA
ITU-T V.90
performance.
The HS Modem family includes a
ITU-T V.92
unique low distortion DAA designed for optimal
performance over all PSTN line conditions thereby
achieving the most reliable and best performance
PSTN connections.
2007 Cermetek Microelectronics, Inc.
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Document No. 607-0020 Revision B (01/07)
Cermetek Microelectronics, Inc.
CH179XA/2056A High Speed Family of Ultra Small Modems
Error Correction. Error correction is enabled via the
\Nn command.
Enabling error correction overrides
&Qn and sets S36 and S48 values.
Refer to
Cermetek, “AT Commands and S-Registers”, for a
more detailed discussion.
The HS Modem supports V.42 LAPM, MNP 2-4, MNP
10 error correcting protocols.
The CH1794A uses
MNP5
data
compression
techniques
and
the
CH1799A/CH2056A uses V.42bis and V.44 data
compression, allowing data transmission rates of up to
a
maximum
of
57.6kbps/115.2kbps/230.4kbps,
respectively.
These high DTE data rates are
supported by the HS Modem serial interface via its
auto baud capability. Note that the maximum speed
attained is limited by the maximum speed available
from the DTE.
IMPORTANT NOTE
Figure 2. Example of Off Hook Indication using
The V.92 standard prescribes 56kbps downlink and
“H” version HS Modem and external LED and
48.8kbps uplink. Consequently, two V.92 modems
resistor.
connected back-to-back will transmit at 48.8kbps
(maximum).
NOTE
The minimum transmission rate is not stored and will
Ring Indicator (RI). The RI pin follows the frequency
default to 300bps upon execution of reset or upon
of the ring signal and toggles low when the modem
power up.
detects an incoming call. The ring signal is typically 20
to 30 Hz and is on for 2 seconds and off for 4 seconds.
Refer to, “AT Commands and S-Registers”, for a more
Although not TTL compliant, the RI pin can,
detailed discussion of the +MS command.
nonetheless, be utilized to activate external circuitry
including the external RST pin.
CONNECTING TO THE HOST UART
Off-Hook Indicator (OHI). The “H” version of the HS
Since a modem communicates data serially and most
Modem provides an active high signal on the OHI pin
host products handle data in a parallel format, a UART
(Pin # 18) indicating when the HS Modem goes off-
is needed to make parallel-to-serial and serial-to-
hook. The circuit in Figure 2 can be used to drive an
parallel translations.
external LED.
Note that the OHI output active (or
high) is 2.75-3.25 volts.
SUPPORTED FEATURES
+MS Command.
The user may override the
AT Command Set. The HS Modem supports the AT
automatic data rate function of the HS modems. This
Command set with extensions and can operate with
is accomplished by executing the +MS command.
industry standard communication software. The AT
This command allows the user to specify the desired
Commands are compatible with TR302.2/88-08006.
data modulation protocol. Further, the +MS command
may be used to force a desired data rate and/or
Serial Host Interface.
The HS Modem family
restrict the allowed data rate.
The supported
operates in asynchronous mode and supports a 5V,
modulation schemes are listed above.
RS232- like interface called V.24 (EIA-232-E). Signal
levels are TTL rather than RS-232C level compatible,
which allows direct connection of the HS Modem to the
The
following
examples
establish
the
V.22bis
host’s UART without level translating circuitry. See
modulation scheme:
Table 3 for a complete set of pin descriptions.
Enter:
AT+MS=V22B
The modem is controlled by sending serial commands
Result:
OK
over TXD and by monitoring serial status messages
returned on RXD. All other serial interface lines may
This is identical to the following explicit +MS
be utilized for the convenience of a particular
command:
application but are not required by the modem.
Unused outputs from the HS Modem should be left
Enter:
AT+MS=V22B,0,300,1200,300,1200
unconnected.
Unused inputs should be tied to the
Result:
OK
proper logic level. See Table 3.
2007 Cermetek Microelectronics, Inc.
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Document No. 607-0020 Revision B (01/07)
Cermetek Microelectronics, Inc.
CH179XA/2056A High Speed Family of Ultra Small Modems
Speaker Interface.
The SPK output reflects the
Failure to provide such operating conditions could
receiver analog input and provides a signal that can be
cause the HS Modem to malfunction or to function
used to monitor call progress. The SPK signal can
erratically.
drive a 300-ohm load directly.
Typically, the SPK
signal is input into an audio power amplifier and the
The HS Modem family requires +5V ±5% supply. It is
amplifier, in turn, drives the speaker coil. The speaker
recommended that bypass capacitors be placed on the
is activated with the ATMn command. The speaker
power supply as close to the HS Modem’s supply input
volume is adjusted using the ATLn command; where n
pins as practical. It is recommended that a 10 µF or
is 0, 1, 2, or 3. Increasing numbers correspond to
greater tantalum capacitor in parallel with a 0.1 µF
higher volume.
Figure 3 indicates one method of
ceramic capacitor be used.
The user must also
driving an external 8-ohm speaker.
provide shielding from nearby sources of EMI, such as
relays, motors and other power supplies.
Sleep Mode. To minimize power consumption, the
HS Family of Modems includes a power reduction
Automatic Speed/Format Sensing. The HS Modem
feature called Sleep Mode. When activated, the HS
supports both Command and Data modes of
Family of Modems will automatically enter Sleep Mode
operation.
after 1 to 255 seconds of inactivity.
The inactivity
delay is selected using the S24 register. The S24 is
set to default to 0 by the factory which disables this
feature. The HS Family of Modems returns to normal
operation when a ring signal is received or upon an
input low signal on the TXD pin.
In Sleep Mode,
power is reduced to about 1/3 of normal operating
power.
30K
Zero Power Mode. The “P” versions of the HS Family
of Modems support Zero Power Mode operation. If an
application calls for zero power during standby
periods, this feature allows the power to the HS
Modem to be switched off using external circuitry and
then reapplied when the modem’s RI pin becomes
active. The HS Modem can thus be powered down to
zero current.
Referring to Figure 3, the controller activates the relay
switch, supplying power (+5V) to the HS Modem. In
this configuration, the ring signal is used to “wake up”
the HS Modem when the HS Modem is in the zero
Figure 3. Example of Zero Power Operation.
power state.
The HS Modem can automatically determine the
The user supplies an external pull-up resistor
speed and format of the data sent from the DTE over
(Cermetek recommends 30k ohms) to an active 5V
the serial interface; and can sense the following broad
source to limit the current drawn by the when the HS
range of speeds:
Modem is in zero power mode. An internal blocking
diode provides supply isolation.
CH1794A
300, 600, 1200, 2400, 4800, 7200,
9600, 12000, 14400, 19200, 38400, and
The pins of the HS Modem will be in an undefined
57600bps.
state when powered is switched off. This must be
CH1799A
300, 600, 1200, 2400, 4800, 7200,
taken into consideration to assure that no unwanted
9600, 12000, 14400, 16800, 19200,
signals are presented to the HS Modem during zero
21600, 24000, 26400, 28800, 38400,
power operation.
57600, and 115200bps.
CH2056A
300, 600, 1200, 2400, 4800, 7200,
Power Supply. The HS Modem module is a complex
9600, 12000, 14400, 16800, 19200,
set of sensitive subsystems.
During the course of
21600, 24000, 26400, 28800, 38400,
normal operation, the HS Modem decodes analog
57600, 115200, and 230400bps.
signals from the telephone line that are in the millivolt
range. Steps must be taken by the user to guarantee
The data formats in Table 1 are recognized by the HS
that power supply noise on all supply lines, including
Modem family of products. The HS Modem can sense
ground, does not exceed 25mV peak to peak.
If
data with mark or space parity and configures itself as
necessary, use dedicated power and ground planes.
described in Table 2.
2007 Cermetek Microelectronics, Inc.
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Document No. 607-0020 Revision B (01/07)
Cermetek Microelectronics, Inc.
CH179XA/2056A High Speed Family of Ultra Small Modems
The HS Modem is trained to a selected speed with an
application, use a relay or zero impedance switch to
AT<CR> training sequence. Thus, the DTE to modem
disconnect T1 when in data mode.
serial interface speed can be set independent of the
DCE or line carrier connecting speed (with minor
When voice and data are both being used, and the T1
restrictions, see the AT+ MS command). This allows
pin is active, it is typical for voice communication to
greater flexibility when selecting DCE line carrier
precede data communication.
In this case, the
modulation speed thereby affording the user with
following commands should be used to configure the
optimum data throughput performance. To maximize
HS Modem to allow for full utilization of the Voice/Tone
effective modem data throughput speed, the DTE to
injection feature.
These commands disable auto-
modem serial interface speed should be set to the
answer and eliminate hang-up due to lack of carrier
highest speed available without invoking the use of the
signal.
HS Modem’s built-in flow control.
Although flow
control facilitates communication with higher speed
1. Enter: ATS0=0<CR>
modes by the DTE, use of flow control causes an
2. Enter: ATS7=255<CR>
overall throughput data rate penalty.
3. Enter: ATS10=255<CR>
Table 1. Data Formats Recognized by HS Modem
Family.
No. of
Character
Data Length
Stop
Length
Parity
(No. of Bits)
Bits
(No. of Bits)
None
7
2
10
Odd
7
1
10
Even
7
1
10
None
8
1
10
Odd
8
1
11*
Even
8
1
11*
*11 bit characters are sensed, but the parity bits are
stripped off during data transmission in Normal and
Error Correction modes.
Figure 3. Speaker Control Circuit.
Voice/Tone Injection Port. The HS Modem Family
The
following
command
sequences
illustrate
provides pin T1 to allow the user to share the PSTN
implementation
of
common
voice/tone
port
line interface associated with the modem for voice and
applications.
DTMF applications.
Figure 5 contains a schematic
which uses a 5 Volt single supply operational amplifier
1. To answer a voice call:
and indicates one possible configuration for voice/tone
(a) Enter: ATH1<CR>
utilization.
(b) Switch local voice source into T1
(c) Begin Voice Conversation
Refer to Cermetek Application Note #170, 2-4 Wire
Converter for Use with CH179X and CH2056 Modems,
2. To switch to data mode, switch local voice source
for an alternative voice/tone implementation that
from T1:
utilizes dual supply operational amplifiers.
(a) At the Originate Modem, enter: ATX1<CR>
(b) At the Answer Modem, enter: ATA<CR>
Table 2. HS Modem Auto Configuration Based on
DTE Configuration .
3. To disconnect (hang-up) a voice call or data call:
DTE Configuration
HS Modem
(a) Return to control mode by entering: +++
Configuration
(b) Enter: ATH<CR>
7 mark
7 none
7 space
8 none
4. To place a voice call using the HS Modem DTMF
8 mark
8 none
facilities:
8 space
8 even
(a) Enter: ATDT1234567<CR>
Where 1234567 is the phone number
All HS Modem products are designed with pin T1
(b) Then switch to local voice source
coupled directly to the internal DAA. When using the
HS Modem in data mode, T1 should float and be
Modem-on-Hold (MOH). The Modem-on-Hold (MOH)
disconnected from any potential signal because any
feature enables the CH2056A modem to temporarily
signal on T1 during data operation will affect the HS
pause a data call to the Internet by placing the call on
Modem’s output. If T1 is being asserted from another
hold to allow usage of the same PSTN line to accept
an incoming call or to initiate an outgoing voice call.
2007 Cermetek Microelectronics, Inc.
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Document No. 607-0020 Revision B (01/07)
Cermetek Microelectronics, Inc.
CH179XA/2056A High Speed Family of Ultra Small Modems
This feature is available only with a connection to an
WARNING
ISP server supporting MOH. MOH can be executed
The HS Modem family of products has been FCC
using the +PMH and +PCW commands.
Refer to
Part 68 approved as data/FAX modems. Utilization
Cermetek document AT Commands and S-Registers,
of the Voice/Tone Port requires further registration.
for more details.
The FCC requires that the entire system, including
the HS Modem and the handset or DTMF
Quick Connect. The Quick Connect feature enables
transceiver, adhere to Part 68 rules.
the CH2056A modem to shorten the connect time of