HIGH SPEED Modem and FAX FAMILY
CH2056
CH1799
CH1798
CH1794
INTRODUCTION
The CH2056, CH1799, CH1798 and CH1794 (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 56,000bps. By using built in compression
algorithms the operating speed can be expanded to the
maximum DTE rate of 57.6kps for the CH1794, 115.2Kbps
for the CH1798/CH1799 and 230.4kbps for the CH2056. 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 CH1799LL operates
exclusively on non-voltage bearing leased line.
The HS Modem family is pin compatible with Cermetek’s low
cost CH1786 V.22bis, 2400bps modem family. Each module
in the HS Modem family is a self-contained modem and is
FCC Part 68 approved and Canadian DOT approveable.
These ultra small modules are designed for PCB through-
hole mounting and are 1.35” x 1.38” x 0.58” in size. The HS
Modem family requires only two external interfaces: a CCITT
V.24 serial interface that can be routed directly to a UART,
and a Tip and Ring interface which goes directly to an 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.
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FEATURES
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V.90 / 56,000bps
V.34bis / 33,600bps
V.34 / 28,800bps
V.32bis / 14,400bps
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Supports V.90, V.34bis, V.34, V.32bis, V.32, V.22bis,
V.22A/B, V.23, V.21, Bell 212A and 103
CH2056 supports V.80 Synchronous operation
Error correcting: V.42 LAMP, MNP 2-4 and MNP 10
Data Compression: V.42bis and MNP 5
MNP10 Data throughput enhancement for cellular
operation
DTE serial interface with speeds up to 230.4kbps
(CH2056), 115.2kbps (CH1799/CH1798) or 57.6kbps
(CH1794)
Automatic baud rate adaptability utilizing speed sensing,
flow control and data buffers
Send & Receive Fax Class 1, Group 3 supported
Serial V.24, 5 volt interface
NVRAM directory and stored profiles
AT Command structure, with extensions
Built-in DAA with 1500 VAC RMS isolation 2122V peak
surge protection
UL 1950 and CSA C22.2 950 Recognized
Leased Line version available CH1799LL
FCC part 68 Approved/DOT CSA CS-03 Part I
Approveable
+5 Volt operation with zero power option
Small size: 1.35” x 1.38” x 0.61” (nominal)
Pin compatible with low speed/low cost CH1786
Figure 1. Function Block Diagram of HS Modem Family.
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 the DTE step
up or step down in speed based on the incoming or out-going
PSTN communication data rate. Hence, the DTE can train
the CH2056, to say 56kbps, and talk to a slower incoming
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.
Non-Volatile RAM (NVRAM).
NVRAM can store two 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
©2000
Cermetek Microelectronics, Inc.
upon reset or power up. The ATZn command immediately
recalls and activates a stored configuration. See Tables 7A
and 7B for storable S-Registers and Commands.
The NVRAM can save up to four telephone numbers, with up
to 36 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.
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Documt No. 607-0003 Revision G (05/00)
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.
The HS Modem family is designed to meet North American
telephone standards as set by 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
described in Figure 6A and 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. With the
exception of the U.S., most countries (including Canada)
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 the
industry modem standards listed below.
Bell 103
Bell 212A
CCITT V.22
CCITT V.22bis
CCITT V.32
CCITT V.32bis
CCITT V.34
CCITT V.34bis
CCITT V.90
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). The HS Modem supports a full RS-232C/V.24 serial
interface. 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.
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 Atm 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.
Zero Power Mode.
If an application calls for zero power during standby periods,
the power may be switched off using external circuitry and
then reapplied when the HS Modem’s RI pin becomes
active. The HS Modem can thus be powered down to zero.
Referring to Figure 2, 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 power down state.
The pins of the HS Modem will be in an undefined state
when power is switched off. This must be taken into
consideration to assure that no unwanted signals are
presented to the HS Modem during power down.
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 25 mV peak to peak. If
necessary, use dedicated power and ground planes. Failure
to provide such operating conditions could cause the HS
Modem to malfunction or to function erratically.
The HS Modem supports V.42 LAMP, MNP 2-4, MNP 10
error correcting protocols. The CH1794 uses MNP5 data
compression techniques and the CH1798/9/CH2056 uses
V.42bis 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.
The resident Modulator/Demodulator
equalization and forward error correction.
supports
line
©
2000 Cermetek Microelectronics, Inc.
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Document No. 607-0003 Revision G (05/00)
The HS Modem Family requires a single +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.
Figure 2. Zero Power Operation.
flow control causes an overall throughput data rate penalty.
Table 1. Data Formats Recognized by HS Modem
Family.
Character
Length
(No. of Bits)
10
10
10
10
11*
11*
Parity
None
Odd
Even
None
Odd
Even
Data Length
(No. of Bits)
7
7
7
8
8
8
No. of
Stop Bits
2
1
1
1
1
1
*11 bit characters are sensed, but the parity bits are
stripped off during data transmission in Normal and
Error Correction modes.
Table 2. HS Modem Auto Configuration Based on DTE
Configuration.
DTE Configuration
7 mark
7 space
8 mark
8 space
HS Modem Configuration
7 none
8 none
8 none
8 even.
Automatic Speed/Format Sensing.
The HS Modem supports both Command and Data modes of
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:
300, 600, 1200, 2400, 4800, 7200, 9600, 12000,
14400, 19200, 38400, and 57600bps
CH1798/9 300, 600, 1200, 2400, 4800, 7200, 9600, 12000,
14400, 16800, 19200, 21600, 24000, 26400,
28800, 38400, 57600 and 115200bps
CH2056 300, 600, 1200, 2400, 4800, 7200, 9600, 12000,
14400, 16800, 19200, 21600, 24000, 26400,
28800, 38400, 57600, 115200 and 230400bps
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.
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
CH1794
Figure 3. Speaker Control Circuit.
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 indicating one possible configuration for
voice/tone utilization.
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 application, use a relay or zero
impedance switch to disconnect T1 when in data mode.
Referring to Figure 5, use the variable resistor (POT) to set
required speaker volume.
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©
2000 Cermetek Microelectronics, Inc.
To maintain FCC compliance, frequencies transmitted while
in voice mode should be between 300Hz and 3000Hz.
When voice and data are both being used, and the RXA and
TXA pins are 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.
2.
3.
Enter:
ATS0=0 [CR]
Enter:
ATS7=255 [CR]
Enter:
ATS10=255 [CR]
serially on the TXD pin. After execution of a received
command, the modem returns a serial status message that
can be read on pin RXD.
This message indicates
command completion status. Refer to Tables 5A, 5B and
5C for a complete list of status messages.
MODEM STATES
The HS Modem can be in either command mode or data
mode. When the modem is idle, it is in command mode by
default and will recognize commands.
When data
transmission is in progress, the HS Modem is in the data
mode state and will not recognize commands. To force the
HS Modem to recognize commands, the host must send an
“escape sequence” to the HS Modem forcing it out of data
mode and into command mode.
The escape sequence consists of a “guard time” (a period
where no characters are sent to the modem), followed by 3
escape characters, followed by another guard time. At
power-up, the guard time is set to 1 second minimum, and
the escape character is set as “+.” These two parameters
can be modified via registers S2 and S12, respectively.
The HS Modem will stay off-hook with its carrier on after the
escape sequence is received and it returns an OK status
message when it is ready to accept commands. The HS
Modem can be put into data mode by issuing the command
ATO [CR].
The following command sequences illustrate implementation
of common voice/tone port applications.
1.
To answer a voice call:
(a) Enter:
ATH1 [CR]
(b) Switch local voice source into RXA and TXA
(c) Begin voice conversation.
To switch to data mode, switch local voice source from
RXA and TXA:
(a) At the Originate Modem, enter:
ATX1 [CR]
(b) At the Answer modem, enter:
ATA [CR]
To disconnect (hang-up) a voice call or data call:
(a) Return to control mode by Entering:
+++
(b) Enter:
ATH [CR]
To place a voice call using the HS Modem DTMF
facilities:
(a) Enter:
ATDT(Tele)#;[CR]
(b) Then switch to local voice source
2.
3.
THE COMMAND FORMAT
Typical commands consist of three elements:
1. The attention sequence,
2. The commands themselves and
3. A terminating carriage return.
WARNING: The HS Modem family of products has been
FCC Part 68 approved as data/FAX modems. Utilization
of the Voice/Tone Port requires further registration. The
FCC requires that the entire system, including the HS
Modem and the handset or DTMF transceiver, adhere to
Part 68 rules.
4.
MODEM CONTROL
The HS Modem may be controlled by sending serial ASCII
command sequences. The commands are sent to the modem
Figure 4. HS Modem Family Application Diagram.
©
2000 Cermetek Microelectronics, Inc.
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Document No. 607-0003 Revision G (05/00)
AT [commands] [CR].
Where:
[AT]
represents attention sequence.
[commands]
represents command strings.
[CR]
represents carriage return (ASCII 13 or HEX 0D).
When entering commands to the modem, the backspace
character-control-H (ASCII 8 or HEX 08) can be used to edit
mistakes. “AT” and “A/” may not be edited however. Multiple
commands may be placed in the command line. A command
line may be as long as 40 characters, excluding the letters
AT. By way of example, the command below instructs the
HS Modem to configure itself to not echo characters when in
command mode (E0) and then put itself in answer mode (A).
Enter:
ATE0A[CR]
AT Command Set.
The available command set is divided into four types of
commands : dial modifiers, basic commands, ampersand and
percent commands. Refer to the complete list in Tables 6A
and 6B.
Enter:
AT[CR]
Where:
A
and
T
may be either upper or lower case but
must be the same case.
[CR]
represents carriage return
The “AT” sequence is referred to as an attention sequence.
The HS Modem will respond with one of the following status
messages, depending on whether it is optioned for
abbreviated or English status messages.
Result:
0[CR]
(Abbreviated form)
Result:
[CR][LF][OK][CR][LF]
(English form)
Where:
[CR]
represents carriage return (ASCII 13 or
HEX 0D).
[LF]
represents line feed (ASCII 10 or HEX 0A).
The modem is now in idle mode and is ready to accept
commands.
An alternate attention sequence “A/” may be sent which
behaves much like the AT sequence except that it causes
the previously entered command specified with an AT prefix
to be executed. When given, it must be in upper case
ASCII. No carriage return is needed.
INITIALIZING THE MODEM
Before commands may be sent to the HS Modem, the
modem must be initialized. This consists of two events:
1. Modem Reset. This is accomplished by applying a
hardware reset pulse to pin RST or by switching the
power off and then back on.
2. Initial Modem Training. The modem must be trained to
the host DTE speed and parity (odd, even, mark, space
or none). These activities are briefly described below.
Reset.
Upon applying power to the HS Modem, the HS Modem
automatically generates an internal reset pulse. The user
can also reset the modem externally by applying a high-going
reset pulse to the RST pin for at least 10ms after the +5V
power supply has stabilized. Delay sending commands to
HS Modem for 900ms after reset has been initiated to allow
the HS Modem time to properly reconfigure.
On power up, or when reset is initiated either by command
(ATZ) or by the RST pin, the modem will reconfigure to its
default state with the line carrier modulation speed set to:
1.
2.
3.
4.
14.4kbps for the CH1794
28.8kbps for the CH1798
33.6kbps for the CH1799
56.0kbps for the CH2056
STATUS MESSAGES AND RESULT CODES
A result code is issued by the HS Modem to the DTE for all
commands executed by the HS Modem, except dialing
commands. Further, various activities on the PSTN are also
signaled to the DTE by the HS Modem.
All result codes have either a terse, short form version
(which is identified by a number followed by a [CR]) or a
verbose long form English-like message version (which is
preceded and terminated with a [CR] and line feed).
The user may suppress certain subsets of the non-extended
result codes. This is accomplished by selecting subsets of
the result code set using the ATXn command, where n=0, 1,
2, 3. Optionally, the user may specify an extended set of
result codes (codes above 35) by setting Register S95. See
the detailed description of result codes in Table 5A, Table
5B and Table 5C.
All AT commands, other than dialing commands, will be
responded to with either an OK (short form result code 0) if
the command is valid or accepted, or with an ERROR (result
code 4) if the command is not recognized. The detail
contained in the error result codes signaled to the DTE
depends on the level of message suppression employed by
the user. As can be seen from Tables 5A, 5B and 5C,
specifying X4 allows the HS Modem to utilize the entire
range of non-extended messages, whereas X0 suppresses
all but the very basic result codes. Most of the result codes
allowed under X1, X2 and X3 are considered call progress
status codes and, in practice, are suppressed except for the
case of debugging activities. It is recommended that the
non-extended result codes be used in all cases.
It should be noted that the default connect result codes 9-20
indicate DTE connection speed, not Carrier Line DCE
speed. Hence, a CH1794 will connect at a maximum speed
of 19.2kbps (result code 16). The CH1798 and CH1799 will
connect at a maximum DTE speed of 38.4kbps (result code
17) and the CH2056 will connect at a maximum speed of
57.6kbps (result code 18) unless the DTE is forced to a
If desired, any speed, error correction, or data compression
method available on the HS Modem can be locked in, using
the AT\Nn and/ or AT+MS commands.
Training the Modem.
Each modem must be trained to match the host DTE speed
and parity so that it is able to recognize serial asynchronous
commands sent to it by the DTE.
The DTE must retrain the modem each time a reset pulse is
applied on RST or after a RESET serial command has been
issued.
Modem Training Command Sequence.
The HS Modem is trained by sending it the following
sequence:
©
2000 Cermetek Microelectronics, Inc.
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Document No. 607-0003 Revision G (05/00)
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