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