CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 1 Document No. 607-0019 Revision A8 (03/06)
INTRODUCTION
The CH1786A represents the next generation of full
function, FCC Part 68 approved 2400bps modems in
the CH1786 Family. These modems provide a fast,
easy and flexible way to integrate a modem into any
OEM product while utilizing the minimum amount of
PCB space (1.01”x 1.27”x 0.52”). The CH1786A
family only requires two external interfaces: a ITU-T
V.24 serial interface that can be routed directly to a
UART, and a Tip and Ring interface which goes
directly to an RJ-11 jack for the PSTN line connection.
The CH1786A can be controlled with industry standard
AT commands and, hence, is compatible with
available industry communication software. DTE
speed conversion allows commands and data to be
sent at rates that differ from the modem connection
speed. In most cases, the CH1786A can be used
interchangeably with the CH1786. See Attachment I
for equivalency comparisons and differences by
product.
All CH1786A modems support asynchronous
operation at 2400bps, 1200bps, and 300bps to both
Bell and ITU-T standards. The CH1786A also
supports Fast Connect and LAPM/MNP Error
Correction.
The resident PSTN line interface, or Data Access
Arrangement (DAA), while being FCC approved, is
also Industry Canada CS-03 Part I Registered.
Further, the CH1786A can be approved in other
countries that require 1500VAC RMS isolation
requirements per UL 1950 Edition 3.
The CH1786A family of modems operate off a single
5-volt supply. The low power operation and automatic
standby mode make these modems ideally suited for
portable equipment. In addition, their small physical
size affords maximum flexibility in equipment design.
CH1786A comes with FCC Part 68 approval and is
shipped from the factory with an FCC Part 68 label
indicating the registration number and ringer
equivalent. This label should be prominently displayed
on the end product.
FEATURES
• Supports Standards ITU-T V.22bis, V.22, Bell 212,
and Bell 103.
• FCC Part 68 approved:
US:B46MM07BCHXXXXAYY
• Industry Canada CS-03 Part I Registered:
IC:176A-CHXXXXAY
• UL 1950 Edition 3 and CSA C22.2 950 Listed.
• UL File Number: E251266.
• AT Command structure with extensions.
• 1500 VAC RMS isolation barrier minimum, 2122V
peak surge protection minimum.
• Error Correction.
• Fast Connect (V.22).
• Single 5 volt operation.
• Caller ID (optional).
• Low power operation with automatic reduced power
standby mode.
• Zero Power (optional).
• Automatic adaptive and fixed compromise
equalization.
• Size: 1.01”x 1.27”x 0.52” (nominal).
• NVRAM allows storage of custom configurations
and telephone numbers.
Figure 1. Functional Block Diagram of CH1786A.
DESCRIPTION OF FUNCTIONAL BLOCKS
AND DISCUSSION OF BASIC OPERATIONS
Figure 1 contains a functional block drawing of the
CH1786A. The CH1786A is a highly integrated, full-
function modem, comprised of a modulator/
demodulator, controller, NVRAM and an FCC Part 68
approved and UL 1950 Edition 3/CSA C22.2 950 listed
PSTN line interface.
Modulation/Demodulation and Modem Controller.
These functions are provided by a monolithic modem
integrated circuit. This IC has built-in facilities to
accommodate integrated AT command control and
contains the necessary resident interfaces for general
communication and routing to the DAA.
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Telephone Line Interface or DAA. The CH1786A
Figure 2. Voice/ Data Port Control
family of modems is designed to meet 1500VAC RMS
isolation and provide 2122V peak surge protection.
Consequently, the CH1786A satisfies U.S. FCC Part
68 and Industry Canada CS-03 Part I requirements,
and will meet other international approval agency
requirements that specify these levels of isolation.
With the exception of the U.S., most countries
(including Canada) require submission of the final
product or system containing the CH1786A 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 or consultant
then forwards the test results and applicable
documents to the regulatory agency. Call Cermetek
for a list of suggested consultants.
Non-Volatile RAM (NVRAM). The NVRAM present
on the CH1786A is sufficient to store up to two user
customized modem profile configurations. The
AT&Wn command will store the active modem
configuration in the selected NVRAM profile by
specifying either an n of 0 or 1. The CH1786A is
delivered with Factory Default setup parameter values
pre-stored in NVRAM profile 0.
The AT&Yn command selects the modem
configurations to be automatically recalled and made
active upon a reset or power up. The ATZn command
immediately recalls and activates a stored profile
configuration. Refer to Tables 4, 5 and 6 for storable
S-Registers and available 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 individual NVRAM
telephone number storage locations are selected by
specifying an n of 0, 1, 2, or 3. The ATDTS=n
command will cause the modem to dial the stored
telephone number in location n.
SUPPORT FEATURES
AT Command Set. A 50-character command line is
supported. The command line starts with AT and may
contain standard or enhanced commands. The
commands are compatible with EIA Document
TR302.2/88-08006.
Serial Host Interface. The serial interface is a V.24
(EIA-232) compatible interface. Ten Bits total: 1 start
bit, 1 stop bit, and eight data bits which can be either
eight bits with no parity or seven odd or even with
parity. The start bit is LOW going. RXD and TXD data
is non-inverted. See pin description in Table 2.
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 Ω 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 5 indicates one method of
driving an external 8 Ω speaker.
Phone Control. Cermetek’s CH1786A contains a pin
called Voice or Data (V/D). The V/D pin toggles high
when the modem goes off hook. This pin can be used
to activate a relay which can switch a telephone on or
off the Tip and Ring incoming PSTN lines. This
feature allows any telephone associated with the
CH1786A to be disconnected when a data call is in
progress, thereby preventing the data from being
disturbed by an inadvertent telephone pick-up. See
Figure 2.
Speed and Parity Selection. Prior to call initiation,
the host controller trains the modem to the host speed
(2400, 1200 or 300bps) and parity (odd, even, mark,
space, or none) via a host-initiated training sequence.
This training also sets the speed of the data for
originate calls. The CH1786A will automatically adjust
to the originator’s speed when answering calls.
The CH1786A matches the host’s parity when it
returns status messages to the host. During a data
connection, however, the modem passes parity
through without interpretation or alteration.
Sleep Mode. To minimize power consumption, the
CH1786A includes a power down feature called Sleep
Mode. When activated, the CH1786A will
automatically enter Sleep Mode after 1 to 255 seconds
of inactivity. The inactivity delay is selected using the
ATS24 command and defaults to 0 which will disable
this feature. The CH1786A returns to normal
operation when a ring signal is received or upon an
input low signal on the TXD pin. A SLEEP output
signal is available to control power to external devices.
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In Figure 5, a FET controlled by the SLEEP signal
turns off the external speaker amplifier when the
CH1786A enters Sleep Mode. In Sleep Mode, power
is reduced to about 1/3 of normal operating power.
Zero Power Mode. The “P” versions of the CH1786A
Family supports Zero Power Mode operation. If an
application calls for zero power during standby
periods, this feature allows the power to the CH1786A
to be switched off using external circuitry and then
reapplied when the CH1786A’s RI pin becomes active.
The CH1786A can thus be powered down to zero.
Referring to Figure 3, the controller activates the relay
switch, supplying power (+5V) to the CH1786A. In this
configuration, the ring signal is used to “wake up” the
CH1786A when the CH1786A is in the zero power
state.
Figure 3. Zero Power Operation.
As indicated in Figure 2, the user connects an external
pull-up resistor (Cermetek recommends 30k ohms) to
an active 5V source thereby providing a small current
to the CH1786A through the RI pin when the CH1786A
is powered down (i.e., no power applied to the VCC
pin). An internal blocking diode provides supply
isolation.
The pins of the CH1786A 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 CH1786A during power down.
Guard Tone. A guard tone of 550 Hz or 1800 Hz can
be generated at 6 dB or 9 dB below the transmit level,
respectively, by using the &Gn command. For a more
detailed discussion, refer to Cermetek Document 613-
0001, “AT Commands and S-Registers”, which can be
found on the Cermetek web site located at
http://www.cermetek.com.
Answer Tone. A ITU-T (2100 Hz) or Bell (2225Hz)
answer tone is generated depending on the selected
configuration. Refer to “AT Commands and S-
Registers” for a more detailed discussion.
Data Encoding. The data encoding conforms to ITU-
T recommendations V.22bis or V.22, or Bell212A, or
103, depending on the selected configuration. Refer
to “AT Commands and S-Register” for a more detailed
discussion.
Line Equalization. Transmitter and receiver digital
filters compensate for delay and amplitude distortion
during operation on nominal phone lines. In addition,
automatic adaptive equalization in the receiver
minimizes the effects of inter symbol interference.
Transmission Speed. In normal operation, the
originating modem initiates the call and attempts to
connect to the answering modem at a speed
established by the originating modem’s controller prior
to call initiation. This is referred to as the Initial
Trained Rate. Upon receiving the call, the answering
modem will attempt to connect to the originating
modem at its Initial Trained Rate. If these two rates
are identical, the connection is made. If the speeds
differ, the answering modem must adjust its rate or
terminate the call. Table 1 indicates the connection
rate when the calling modem’s Initial Trained Rate and
answering modem’s Trained Rate are different.
Error Correction. The CH1786A supports LAPM and
MNP 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.
Table 1. Connection Rates.
Connection Rate Resulting
When Calling Modem Initial
Rate Is:
Answering Modem
Initial Trained Rate
300 1200 2400
300 300 1200 1200
1200 300 1200 1200
2400 300 1200 2400
NOTE
A 2400-baud connection rate will only result if both
modems are initially set at 2400 baud.
Ring Indicator (RI). The RI pin follows the frequency
of the ring signal and toggles low when the CH1786A
detects an incoming call. The ring signal is typically 20
to 30 Hz and is on for 2 seconds and off for 4 seconds.
CH1786A
-
P
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2006 Cermetek Microelectronics, Inc. Page 4 Document No. 607-0019 Revision A8 (03/06)
Although not TTL compliant, the RI pin can,
nonetheless, be utilized to activate external circuitry
including the external RST pin.
+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 establish the V.22bis
modulation scheme:
Enter: AT+MS=V22B
Result: OK
This is identical to the following explicit +MS
command:
Enter: AT+MS=V22B,0,300,1200,300,1200
Result: OK
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.
Power Supply. The CH1786A modem module is a
complex set of sub-systems. During the course of
normal operation the CH1786A 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 50 mV peak to peak. Any
frequency between 20 kHz and 150 kHz must be less
than 500 micro volts peak. If necessary, use
dedicated power and ground planes. Failure to
provide such operating conditions could cause the
CH1786A to malfunction or to function erratically.
The CH1786A requires a single +5V ±5% supply. It is
recommended that by-pass capacitors be placed on
the power supply as close to the modem’s supply input
as practical. It’s recommended a 10 µF Tantalum
capacitor in parallel with a 0.01 µF ceramic capacitor
be used.
Voice/DTMF Tone Injection Port. The CH1786A
provides two pins to allow the user to share the
telephone line interface associated with the modem for
voice and DTMF applications. Figure 4 contains a
schematic indicating one possible configuration for
voice/ tone utilization.
Typically, voice communication would precede data
communications. For this case, the following
commands should be used to configure the CH1786A
(Refer to Figure 4):
Enter: ATS0=0<CR> Disables auto-answer
Result: OK
Enter: ATS7=255<CR> Disables data-carrier time
Result: OK out
Enter: ATS10=255<CR> Disables lost-carrier time
Result: OK out
WARNING
The CH1786A has been FCC Part 68 and Industry
Canada CS-03 Part I approved as a data modem
only. Utilization of the Voice/DTMF Tone Port
requires further registration. FCC and Industry
Canada will require that the system, including the
CH1786A and the handset or DTMF transceiver,
adhere to Part 68 and CS-03 Part I rules.
The following command sequences illustrate
implementation of common Voice/Tone Port
applications.
1. To answer a voice call.
(a) Enter: ATH1<CR>
Result: OK
(b) Drive V.INJ. HIGH to activate relay.
(c) Begin voice conversation.
2. To switch to data mode.
(a) Drive V.INJ. LOW
(b) At the originate modem:
Enter: ATX1<CR>
Result: OK
3. To disconnect (hang-up) a voice call or a data call.
(a) Enter: ATH<CR>
Result: OK
4. Place a call to 1234567 using the CH1786A’s
DTMF tone generator, then use VOICE mode for
voice communications. Note that the CO
command disables carrier generation.
(a) Enter: ATDT1234567;C0<CR>
Result: OK
(b) Drive V.INJ. HIGH
MODEM CONTROL
The CH1786A modem may be controlled by sending
serial ASCII command sequences. The commands
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are sent to the modem 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 Table 3 for a complete list of status
messages.
Figure 4. Voice/Tone Injection.
IMPORTANT NOTE
Although every effort has been made to design the
CH1786A products to be fully and completely
compatible with the existing CH1786 family, there are
some minor differences. Refer to Table 14 for
equivalency information and refer to Attachment I for
a summary of product differences.
INITIALIZING THE MODEM
Before commands may be sent to the CH1786A, the
CH1786A must be initialized. Initialization is a two
step activity consisting of:
1. Hard 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 CH1786A must be
trained to the host’s speed and parity (odd, even,
mark, space or none).
These activities are briefly described below.
Reset. Upon applying power to the CH1786A, the
CH1786A automatically generates an internal reset
pulse. The user may 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 CH1786A for
200ms after reset has been initiated to allow the
CH1786A time to properly reconfigure.
Training the Modem. Each modem must be trained
to match its host’s speed and parity so that it is able to
recognize serial asynchronous commands sent to it by
the host’s is UART. The host 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
CH1786A is trained by sending it the following
sequence:
Enter: AT<CR>
Result: OK
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 CH1786A will respond with one of the
following status messages, depending on whether it is
optioned for Terse (abbreviated) or Verbose (English)
status messages.
Result: 0<CR> (Terse)
or
Result: <CR><LF>OK<CR><LF> (Verbose)
Where: <CR> represents carriage return (ASCII 13
or HEX 0D).
<LF> represents line feed (ASCII 10 or HEX
0A).
After responding with an OK, the CH1786A is in idle
mode and is ready to accept additional 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, both the AT
and A/ must be in upper case ASCII. No carriage
return is needed for the A/ command.
THE COMMAND FORMAT
Typical commands consist of three elements: the
attention sequence, the commands themselves, and a
terminating carriage return.
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)
may be used to edit mistakes. AT and A/ may not be
edited. 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 CH1786A
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to configure itself to not echo characters when in
command mode E0 and then put itself in answer mode
A.
Enter: ATE0A<CR>
Result: OK
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 Table 5.
AT Command Data Rate. With the serial interface,
the rate is speed sensed for parity and format.
THE STATUS MESSAGES
The CH1786A responds with a status message after
each command is executed. This status message
may either be a numeric code (Terse Result Code)
followed by a carriage return; or a carriage return and
line feed with a message in English (Verbose Result
Code) followed by a carriage return and line feed.
Various status code subsets are enabled with the Xn
command. Where n=0, 1, 2, 3, 4 establishes the result
codes allowed to be sent from the CH1786A to the
DTE.
NOTE
The CH1786A is factory set to X4, which allows all
result codes.
MODEM STATES
The CH1786A 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 CH1786A is in
the data mode state and will not recognize commands.
To force the CH1786A to recognize commands, the
host must send an escape sequence to the CH1786A
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. The guard time is set by register S12.
The escape character code is set in register S2. At
power-up, the guard time is set to 1 second minimum,
and the escape character is set as “+.” There is no
minimum delay between characters but the maximum
delay is set by register S12.
The CH1786A will stay off-hook with its carrier on after
the escape sequence is received. It will return an OK
status message when it is ready to accept commands.
The CH1786A may be put into data mode by issuing
the command ATO<CR>.
AT COMMAND APPLICATIONS
Dialing A Phone Number. The Dial command takes
the form Dn, where n is a string of characters. In the
simplest form, n will be only the digits of the phone
number to be dialed.
Example: Dial number.
Enter: ATD1234567<CR>
Result: OK
In response to this command, the CH1786A dials the
telephone number “123-4567” and then waits for a
carrier from the distant modem. If no carrier is
detected within a given time (the default time is 30
seconds), the CH1786A automatically releases the line
and sends a NO CARRIER result code. If a carrier is
detected, the CH1786A gives a CONNECT result code
and goes on-line, permitting communication with the
distant modem.
The Dial Command may also be issued without a
telephone number. ATD causes the modem to pick up
the telephone line without dialing a number.
Pause During Dialing. When placing a call from an
office with a telephone connected to a PBX, it may be
necessary to dial an access code (usually the digit 9)
to get an outside line. Inserting a comma in the
telephone number instructs the modem to pause for a
specific length of time. The factory set default pause
time is 2 seconds.
Example: Dial 9,pause, dial number.
Enter: ATDT9,1234567<CR>
Result: OK
Multiple commas may be used to generate integer
multiples of the specified delay time.
Originate a Call in Answer Mode. The D command
forces the modem into originate mode. To call an
originate-only modem, dial the number and set the
modem to answer mode via the R command (reverse
originate). This is done by including an R at the end of
the telephone number.
Example: Change modem from original-only to answer
mode.
Enter: ATDT1234567R<CR>
Result: OK
Multiple commas may be used to generate integer
multiples of the specified delay time.
Redial Last Number. The repeat command is a
convenient way to execute the previously entered
command line.
Example: Use A/, the repeat command, to redial the
last telephone number dialed.
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Enter: A/
Result: ATDT1234567R<CR> Previous command
OK line executed
Return to Command State. Use ; to return to
command mode offer dialing.
Example: Touch-tone dial 9, pause, dial number,
return to Command.
Enter: ATDT9,1234567;<CR>
Result: OK
V.22 Fast Connect. The CH1786A supports non-
standard V.22 fast connect protocols. This feature
reduces the connect time to 3-4 seconds. However, to
utilize the fast connect protocol, this protocol must be
supported by both modems. Further, the DCE speed
must be set to 1200 baud (i.e., V.22).
To setup the CH1786A to connect utilizing Fast
Connect, execute the following commands:
Enter: AT+MS=V22,0,300,1200,300,1200<CR>
Result: OK
Enter: $F2<CR>
Result: OK
This forces the CH1786A to communicate using the
V.22 protocol and to attempt to connect using Fast
Connect. If Fast Connect is not supported by the other
modem, the CH1786A will connect using the standard
V.22 protocol.
Caller ID (CID). The “C” versions of the CH1786A
Family supports Caller ID. The +VCID command
controls reporting and presentation of the data
provided by the PSTN Caller ID services. Data is
presented to the DTE between the first and the second
ring indication. This command affects the data format
for incoming calls as the call is being received.
Enter: AT+VCID=n&W0&W1<CR>
Result: OK<CR><LF>
IMPORTANT NOTE
The &W0 (or &W1) command, as appropriate per
the specification of &Y0 (or &Y1), must be executed
before the +VCID command will be implemented by
the CH1786A.
Where n is a decimal number corresponding to the
selected option as described below.
0 Disable Caller ID reporting. (Default.)
1 Enables Caller ID with formatted
presentation to the DTE. The data
presented is in a <Parameter Description>
<Value> pair format. The expected pairs
are: date, time, name, and caller code
(telephone number). ASCII data is
presented.
2 Enables Caller ID with unformatted
presentation to the DTE. The data is
presented in a continuous string.
HEXADECIMAL data is presented.
Refer to Application Note # 174, Caller ID Feature For
CH1786A, CH179XA and CH2056A Modems, for
additional information and examples.
The AT+VRID command affects the format of the data
provided by the PSTN Caller ID services for the last
received call. The DTE is presented this data once
every time the +VRID command is executed.
Enter: AT+VRID=n<CR>
Result: Data Stream from most recent call
Where n is a decimal number corresponding to the
selected option as described below.
0 Reports Caller ID with formatted
presentation to the DTE. The data is
presented the data items in a <Parameter
Description> <Value> pair format. The
expected pairs are: date, time, name, and
caller code (telephone number).
1 Reports Caller ID with unformatted
presentation to the DTE.
Refer to Application Note # 174, Caller ID Feature For
CH1786A, CH179XA and CH2056A Modems, for
additional information and examples.
IMPORTANT NOTE
Caller ID (CID) requires that the PSTN service
provider supply the required data. The Caller ID
feature will report the NULL string if the CID service
is not activated by the PSTN service provider.
Automatic Answering. The S0 register controls the
number of rings that must occur before the CH1786A
answers a incoming call. The register may range in
value from 0 to 255.
To set the CH1786A to not answer any incoming calls,
executed the following command:
Enter: ATS0=0<CR>
Response OK
When S0 is set to 0, the modem will not auto-answer.
To set the CH1786A to answer after 3 rings, execute
the following command:
Enter: ATS0=3<CR>
Response OK
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
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Figure 5. CH1786A block diagram illustrating typical feature implementations: V/D control, RJ-11
connection, speaker for call progress monitoring, serial port connection, external reset, +5V and GND.
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Table 2. CH1786A Pin Descriptions
PIN NAME TYPE FUNCTION
1 RING I/O
RING. Directly connects to the telephone line’s Ring lead through a user supplied
RJ-11C jack.
2 TIP I/O
TIP. Directly connects to the telephone line’s Tip lead through a user supplied RJ-
11C jack.
3 RXA O ANALOG VOICE INJECTED. Receive Signal. Let float if not used.
4 TXA I ANALOG VOICE INJECTED. Transmit Signal. Let float if not used
5 SPK O SPEAKER. Audio output for speaker. See speaker control schematic in Figure 5.
6 NC - No connection.
7 NC - No connection.
8 SLEEP O SLEEP. Active LOW. A LOW indicates CH1786A is in low power idle mode. Used
to control power to other devices. See Figure 5. Register S24 is the sleep timer
register. When the CH1786A is inactive for a period of time specified by S24, the
CH1786A will power down by about 1/3 of its normal operating power. During
power down, all I/O lines become undefined. Default is (ATS24=0) disabled.
9 NC - No connection.
10 TXD I TRANSMIT DATA. Active Low. Serial Transmit data input. Marking or a binary 1
condition is transmitted when a HIGH is asserted.
11 RXD O
RECEIVE DATA. Active Low. Serial Receive data output. Received marking or
binary 1 condition is indicated by HIGH.
12 V/D O
VOICE/DATA. Used to switch between telephone and modem line use. In a typical
application, V/D active HIGH opens the normally closed voice injection relay and
disconnects the handset from the telephone line. HIGH indicates the CH1786A is
off-hook and online. Therefore, this pin also reflects the state of the off-hook relay
of the CH1786A. See Figure 2. Let float if not used.
13 DTR I DATA TERMINAL READY. Active LOW. Switching off DTR can either return
modem to command state, disconnect phone call, or reset modem. DTR should be
set LOW when not used.
14 DSR O
DATA SET READY. Active LOW. LOW indicates handshaking with a remote
modem is in progress, and/ or the data carrier of a remote modem has been
detected.
15 RI O
RING INDICATION. This signal follows the frequency of the ringing signal and is
normally about 20 to 40 Hz for 2 seconds on with 4 seconds off. This pin is also
used for Zero Power option. See Figure 3.
16 CTS O CLEAR-TO SEND. Active LOW. Used for hardware Flow Control of data.
17 DCD O
DATA CARRIER DETECT. Active LOW. LOW indicates a data carrier from a
remote modem is detected. Must be enabled using the &C1 command.
18 NC -
No Connection.
19 VCC - POWER SUPPLY. 5 volts + 5%
20 GND - GROUND. Note: Noise should be less than 50mV peak to peak.
21 RST I RESET. Active HIGH. This input must be asserted HIGH for at least 10 ms to reset
the modem. RESET is then returned LOW for normal operation. If no system reset
is available, let this pin float. Input impedance of driving circuit should be <10K.
22 NC I
No Connection.
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2006 Cermetek Microelectronics, Inc. Page 10 Document No. 607-0019 Revision A8 (03/06)
Table 3. S-Register Summary.
Register
Function
Range
Units
Saved
Firmware
Defaults
Factory
Defaults
S0 Rings to Auto-Answer 0-255 rings * 000 001
S1 Ring Counter 0-255 rings 000 000
S2 Escape Character 0-255 ASCII * 043 043
S3 Carriage Return Character 0-127 ASCII 013 013
S4 Line Feed Character 0-127 ASCII 010 010
S5 Backspace Character 0-255 ASCII 008 008
S6 Wait Time before Dial Tone or Blind Dialing 2-255 s * 002 002
S7 Wait Time for Carrier, Silence or Dial Tone 1-255 s * 050 050
S8 Pause Time for Dial Delay Modifier 2-255 s * 002 002
S9 Carrier Detect Response Time 1-255 0.1s * 006 006
S10 Carrier Loss Disconnect Delay 1-255 0.1s * 014 014
S11 DTMF Tone Duration 50-255 0.001s * 085 085
S12 Escape Prompt Delay 0-255 0.02s * 050 050
S13 Reserved - - 000 000
S14 General Bit Mapped Options Status - - * 146 (92H) 146 (92H)
S15 Reserved - - 000 000
S16 Test Mode Bit Mapped Options Status (&T) - - 000 000
S17 POS Option - - 000 000
S19 Reserved - - 000 000
S20 Reserved - - 000 000
S21 V.24/General Bit Mapped Options Status - - 052 (34H) 100 (74H)
S22 Speaker/Results Bit Mapped Options Status - - 117 (75H) 117 (75H)
S23 General Bit Mapped Options Status - 000 000
S24 Sleep Inactivity Timer 0-255 s 000 000
S25 Delay to DTR off 0-255 0.01s 005 005
S26 RTS-to-CTS Delay 0-255 0.01s 001 001
S27 General Bit Mapped Options Status - - 073 (49H) 074 (4AH)
S28 General Bit Mapped Options Status - - 000 000
S29 Flash Dial Modifier 0-255 0.01s 070 070
S30 Disconnect Inactivity Timer 0-255 10ms 000 000
S31 General Bit Mapped Options Status - - 192 (C0H) 192 (C0H)
S36 LAPM Failure Control - - * 007 007
S37 Line Connection Speed - - 000 000
S38 Delay Before Forced Hang-up 0-255 s 020 020
S39 Flow Control Bit Mapped Options Status - - 003 003
S40 General Bit Mapped Options Status - - * 104 (68H) 104 (68H)
S41 General Bit Mapped Options Status - - * 195 (C3H) 192 (C0H)
S43-S45 Reserved - - - -
S46 Data Compression Control - - * 138 136
S48 V.42 Negotiation Control - - 007 007
S82 LAPM Break Control - - 000 000
S86 Call Failure Reason Code 0-26 - 021 021
S91 PSTN Transmit Attenuation Level 0-15 dBm 011 011
S92 FAX Transmit Attenuation Level 0-15 dBm 011 011
S95 Result Code Messages Control - - * 000 000
S210 V.34 Symbol Rate 0-255 - 141 (8CH) 141 (8CH)
NOTES: 1. Parameters indicated with a (*) in the Saved column may be stored in User Profile n=0, 1 by executing
the appropriate &Wn command.
2. A stored Profile is a subset of allowed parameters and is comprised of those parameters displayed
with the &V command.
3. Factory Default values that are different from the Firmware Default values are highlighted in BOLD.
4. Restore Factory Default values using Zn command.
5. Restore Firmware Default values using &Fn command
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 11 Document No. 607-0019 Revision A8 (03/06)
Table 4. Extended Result Code Summary.
Result Code Form n is ATXn
Command
Terse
or
Short
Verbose or Long 0 1 2 3 4
+F4 +FCERROR X X X X X
0 OK X X X X X
1 CONNECT X X X X X
2 RING X X X X X
3 NO CARRIER X X X X X
4 ERROR X X X X X
5 CONNECT 1200 1 X X X X
6 NO DIAL TONE 3 3 X X X
7 BUSY 3 3 3 X X
8 NO ANSWER X X X X X
9 CONNECT 0600 1 X X X X
10 CONNECT 2400 1 X X X X
11 CONNECT 4800 1 X X X X
12 CONNECT 9600 1 X X X X
13 CONNECT 7200 1 X X X X
14 CONNECT 12000 1 X X X X
15 CONNECT 14400 1 X X X X
16 CONNECT 19200 1 X X X X
17 CONNECT 38400 1 X X X X
18 CONNECT 57600 1 X X X X
19 CONNECT 115200 1 X X X X
20 CONNECT 230400 X X X X X
22 CONNECT
75TX/1200RX
1 X XXX
23 CONNECT
1200TX/75RX
1 X XXX
24 DELAYED 4 4 4 4 X
25 MESSAGE-WAITING X X X X X
32 BLACKLISTED 4 4 4 4 X
33 FAX X X X X X
35 DATA X X X X X
39 +MRR: 75 X X X X X
40 +MRR: 300 X X X X X
42 +MRR: 600 X X X X X
44 +MRR: 1200/75 X X X X X
45 +MRR: 75/1200 X X X X X
46 +MRR: 1200 X X X X X
47 +MRR: 2400 X X X X X
48 +MRR: 4800 X X X X X
49 +MRR: 7200 X X X X X
50 +MRR: 9600 X X X X X
51 +MRR: 12000 X X X X X
52 +MRR: 14400 X X X X X
66 +DR: ALT X X X X X
67 +DR: V42B X X X X X
68 +DR: V44 X X X X X
69 +DR: None X X X X X
70 +ER: NONE X X X X X
77 +ER: LAPM X X X X X
Table 4. Extended Result Code Summary
(Continuation).
Result Code Form n is ATXn
Command
Terse
or
Short
Verbose or Long 0 1 2 3 4
80 +ER: ALT X X X X X
81 +ER: ALT-CELLULAR X X X X X
83 LINE IN USE X X X X X
85 OFF-HOOK
INTRUSION
X X X X X
86 LINE REVERSAL
DETECTED
X X X X X
87 NO LINE X X X X X
91 CONNECT 31200
130 +ILRR X X X X X
134 +MCR: B103 X X X X X
135 +MCR: B212 X X X X X
136 +MCR: V21 X X X X X
137 +MCR: V22 X X X X X
138 +MCR: V22B X X X X X
139 +MCR: V23 X X X X X
139 +MCR: V23C X X X X X
140 +MCR: V32 X X X X X
141 +MCR: V32B X X X X X
210 +MRR: 25333 X X X X X
211 +MRR: 26667 X X X X X
212 +MRR: 25333 X X X X X
213 +MRR: 22666 X X X X X
214 DIGITAL LINE
DETECTED
X X X X X
IMPORTANT NOTE
An “X” in a column indicates that the message
(either the long form if verbose, or the value only
for short form) will be generated when that
particular value of “n” (shown at the top of the
column) has been selected by the use of ATXn. A
numeral indicates which less explicit message
(verbose or short form) will be output for that X
option.
The Serial Interface Lines. The CH1786A supports a
full EIA-232E/V.24 serial interface. Signal levels are
TTL rather than EIA-232E level compatible, which
allows direct connection of the CH1786A to the host
UART without the need for level translation circuitry.
See Table 2 for a complete pin description. The
CH1786A is controlled by sending it serial commands
over TXD and it’s status determined by monitoring the
serial status messages returned on
RXD. DTR is optionally used to reset, terminate calls
or return CH1786A to command mode.
All other serial interface lines may be utilized for the
convenience of a particular application but are not
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 12 Document No. 607-0019 Revision A8 (03/06)
Table 5. AT Command Summary.
Command Function
A/ Re-execute command
A Go off-hook and attempt to answer call
B0 Select CCITT connection at 300 or
1200bps
B1 Sect Bell connection at 300 or 1200bps
Dn Dial modifier where n is one or more of
the following:
P Pulse Dial
T Touch Tone Dial
W Wait for Dial Tone
; Return to Command State
@ Wait for Quiet Answer Command
! Flash Hook
, Pause
0-9/ABCD Dial Digits/Characters & wait
for credit card dial tone
^ Toggles calling tone
L Redial last number
*,# Star digit – tone dialing
S=n Dial the number and store in
Directory, n= 0 to 3
E0 Disable command echo
E1 Enable command echo
H, H0 Initiate a hang-up sequence
H1 If on-hook, go off-hook and enter
command mode
L0 Set low speaker volume
L1 Set low speaker volume
L2 Set medium speaker volume
L3 Set high speaker volume
M0 Speaker off
M1 Speaker on during hand shaking and
speaker off while receiving carrier
M2 Speaker on during hand shaking and
while receiving carrier
M3 Speaker off during dialing and receiving
carrier and speaker on during
answering
O0 Go on-line
O1 Go on-line and initiate a retrain
sequence
Sn Select S Register n
Sn=m Write value m to S Register n
Sn? Read the value of S Register n
? Returns Last addressed S Register
value
V0 Short Form Result Code Option
V1 Long Form Result Code Option
X1, X2,
X3, X4
Result Code Reporting Options
+++ Escape Code Sequence
Z0, Z1 The modem performs soft reset.
Restore stored profile 0 or 1 after reset
&C0 Force DCD active regardless of the
carrier state
&C1 DCD to follow the carrier state
Table 5. AT Command Summary (Continuation).
Command Function
&D0 Modem ignores DTR
&D1 Modem assumes command state
&D2 Modem hangs up, assumes
command state and disables auto-
answer
&D3 Modem assumes initialization state
&F0 Restore Factory configuration 0
&F1 Restore Factory configuration 1
&G0, 1, 2 Guard Tone Options
&K0 Disable DTE/DCE flow control
&K1,2 Not Supported
&K3 Enable RTS/CTS DTE/DCE flow
control
&K4 Enable XON/XOFF DTE/DCE flow
control
&K5 Enable transparent XON/XOFF flow
control
&P0, 1, 2, 3 Make to Break Ratio Options
&Q0 Select direct asynchronous mode
&Q1,2,3,4 Not Supported
&Q5 Modem negotiates an error corrected
link
&R0 CTS tracks RTS
&R1 CTS always on
&S0 DSR always on
&S1 DSR active after answer tone
detected and inactive after loss of
carrier
&T0 Terminate Loopback Test
&T1 Initiate Loopback Test
\Bn Send break of n x 100 msec (n=0 to
9)
\N0 Select normal speed buffered mode
\N1 Select direct mode
\N2 Select reliable mode
\N3 Select auto reliable mode
\N4 Force LAPM mode
\N5 Force MNP mode
\V0 Connect messages are controlled by
the command settings X, W, and
S95
\V1 Connect messages are displayed in
the single line format
MODULATION COMMANDS
+MS Select modulation
+MCR=n Carrier protocol n reporting
+MR=n Select extended Modulation
Reporting of +MCR and +MRR to
DTE
+MRR=m, n Report Transmit m and Receive n
DCE rates to DTE
CALLER ID COMMANDS
+VCID Select data presentation format n (0-
2) for incoming calls.
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 13 Document No. 607-0019 Revision A8 (03/06)
Table 5. AT Command Summary (Continuation).
Command Function
+VRID Select data presentation format n (0-
1) for most recently received
incoming call.
ERROR CORRECTING COMMANDS
%C0 Disable data compression
%C1 Enable MNP 5 data compression
%C2 Enable V.42bis data compression
%C3 Enable both V.42bis and MNP 5
compression
STORED PROFILE COMMANDS
&V Display current configuration
&W0 Store the active profile in NVRAM
profile 0
&W1 Store the active profile in NVRAM
profile 1
&Y0 Recall stored profile 0 upon power
up
&Y1 Recall stored profile 1 upon power
up
&Zn=x Store dial string x (31 digits max) to
location n (0-3)
MNP10 COMMANDS
-K0 Disable MNP 10 extended services
-K1 Disable MNP 10 extended services
-K2 Disable MNP 10 extended services
FAX COMMANDS
+FCLASS=n Service Class
+F<cmd>? Report active configuration for
specified command cmd
+F<cmd>=? Report capabilitied for specified
command cmd
+FAA=n Data/Fax Auto Answer
+FLO Flow Control
+FMI? Report Manufacturer ID
+FMM? Report Model ID
+FMR? Report Revisions ID
+FRM=n Receive Data with n protocol
+FTM=n Transmit Data with n protocol
+FRH=n Receive Data with HDLC Framing
with n protocol
+FTH=n Transmit Data with HDLC Framing
with n protocol
+FTS=n Stop Transmission and Wait
FAST CONNECT COMMANDS
$F0 Normal connection (Default)
$F1,3,4 Not Supported
$F2 V.22 Fast Connect
IDENTIFICATION COMMANDS
I0 Reports product code
I3 Reports firmware Identification code
required by the CH1786A depending on user’s
initialization string. Unused outputs (from modem)
should be left unconnected. Unused inputs should be
set to the proper logic level. See Table 2.
Fax Modes. The CH1786A Product Family supports
Send and Receive FAX. The modes and rates are
determined by the AT+F commands. Refer to Table
6A.
FAX modem processing is explicitly defined in ITU-
TV.29, ITU-TV.27, ITU-TV.21 and ITU-T V.17
recommendations. All modulation, wave-form
spectrum, and data processing functions conform to
the appropriate specifications.
PHONE LINE CONNECTION GUIDELINES
1. The CH1786A must be mounted in the final
assembly such that it is isolated from exposure to
any hazardous voltages within the assembly.
Adequate separation and restraint of cables and
cords must be provided.
2. The circuitry from the CH1786A to the telephone
line interface must be provided in wiring that
carries no other circuitry other than that
specifically allowed in the FCC rules (such as A
and A1 leads).
3. Connection to phone line should be made through
an RJ-11C jack.
4. PCB traces from the modem’s RING and TIP pins
to the RJ-11C jack must be 0.1 inch spacing or
greater to one another and 0.2 inch spacing or
greater to all other traces. The traces should have
a nominal width of 0.020 inches or greater.
5. The RING and TIP PCB traces should be as short
as possible and oriented to prevent coupling other
high speed or high frequency signals present on
the host circuit PCB.
6. No additional circuitry other than that shown in
Figure 6 may be connected between the modem
module and the RJ-11C jack. Doing so will
invalidate the FCC approval.
7. Surge protection is provided internally. (See
Figure 6). This is mandatory to maintain FCC Part
68 conveyed approval.
8. The CH1786A, the RJ-11C jack, the interfacing
circuitry and all PCB traces in between, must be
contained on a PCB with a 94 V-0 flammability
rating.
9. The supplied FCC registration label must be
applied visibly on the outside of the product.
10. The product’s User Manual must provide the user
with instructions for connection and use as
recommended in the FCC Registration Section
below.
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 14 Document No. 607-0019 Revision A8 (03/06)
CH1786A HANDLING AND ASSEMBLY
RECOMMENDATIONS
The CH1786A contains static-sensitive components
and should only be handled by personnel and in areas
that are properly protected against static discharge.
The two recommended mounting techniques for
physically connecting the CH1786A to a PCB are
discussed below.
Direct Soldering. The CH1786A may be wave
soldered. All CH1786A products are hermetically
sealed and will not be harmed by industry standard
wave soldering processes.
Socketing. The socketing approach to mounting
eliminates cleaning and desoldering concerns. When
the socket is used, it must make a solid connection to
all pins. Failure to do so will cause unreliable or
intermittent operation. Also, steps should be taken to
assure that the module remains tightly seated in the
socket during shipping. Cermetek recommends using
sockets from Samtec. See Application Note # 130,
Summary of Recommended Suppliers.
Figure 5. Speaker Control Circuit: Optional to
allow for call progress monitoring.
FCC REGISTRATION
All products in the CH1786A family are registered with
the FCC (Federal Communications Commission)
under Part 68. To maintain the validity of the
registration, you must serve notice to the end user of
the products of several restrictions the FCC places on
the modem and its use.
In addition to restriction notification, the FCC requires
that Cermetek make all repairs to all products in the
CH1786A family. If repairs are necessary after
installation of the CH1786A in the end product and the
end product has been delivered to the end user, the
end product must be returned to the end product
supplier where the CH1786A can be removed and
then forward to Cermetek for repair. The following
notice is recommended and should be included in the
end product’s user manual.
FOR YOUR USER’S MANUAL
The FCC Part 68 rules require the following (or
equivalent) be provided to the end user of equipment
containing a DAA.
Type of Service. The (insert end product name) is
designed to be used on standard device telephone
lines. It connects to the telephone line by means of a
standard jack called the USOC RJ-11C (or USOC
RJ45S). Connection to telephone-company-provided
coin service (central office implemented systems) is
prohibited. Connection to party lines service is subject
to state tariffs.
Changes in Attestation Procedure for Plugs and
Jacks. (Name of applicant) attests that the network
interface plugs or jacks used on this equipment comply
with and will continue to comply with the mechanical
requirements specified in Part 68, sub-part F,
specifically the dimensions, tolerances and metallic
plating requirements. The compliance of these
connectors will be assured by purchase specifications
and incoming inspection. Documentation of such
specifications and/ or inspections will be provided to
the FCC within 30 days of their request for the same.
Telephone Company Procedures. The goal of the
telephone company is to provide you with the best
service it can. In order to do this, it may occasionally
be necessary for them to make changes in their
equipment, operations or procedures. If theses
changes might affect your service or the operation of
your equipment, the telephone company will give you
notice, in writing, to allow you to make any changes
necessary to maintain uninterrupted service.
In certain circumstances, it may be necessary for the
telephone company to request information from you
concerning the equipment which you have connected
to your telephone line. Upon request of the telephone
company, provide the FCC registration number and
the ringer equivalence number (REN); both of these
items are listed on the equipment label. The sum of all
of the REN’s on your telephone lines should be less
than five in order to assure proper service from the
telephone company. In some cases, a sum of five
may not be useable on given line. Consult your
telephone provider.
If Problems Arise. If any of your telephone
equipment is not operating properly, you should
immediately remove it from your telephone line, as it
may cause harm to the telephone network. If the
telephone company notes a problem, they may
temporarily discontinue service. When practical, they
will notify you in advance of this disconnection. If
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 15 Document No. 607-0019 Revision A8 (03/06)
advance notice is not feasible, you will be notified as
soon as possible.
When you are notified, you will be given the
opportunity to correct the problem and informed of
your right to file a complaint with the FCC. Contact
your local telephone service provider if you have nay
questions about your phone line.
In the event repairs are ever needed on the (insert
your product name), they should be performed by
(insert your company name) or an authorized
representative of (insert your company name). For
information contact: (insert your company address).
DEFAULT STATUS, PERFORMANCE, AND
SPECIFICATIONS
Factory Defaults. The following is a summary of the
Default Configuration Profile installed by Cermetek
Microelectronics, Incorporated, prior to delivery of the
CH1786A.
Async mode selected
2400bps
Even parity
Auto answer enabled
Command echo ON
Error correction OFF
All result codes enabled –extended
Wait for dial tone before dialing =2 seconds
Detects busy signal
Full word result codes
Pulse dial make/break ratio =39/61
DSR enabled
Modem enabled DTR
DCD enabled
Speaker enabled but off when receiving carrier
Speaker volume set to low
Guard tones disabled
Minimum DTR pulse width =0.1 seconds
Ring count =01
Escape code character =43
Carriage return character =13
Line feed character =10
Back space character =08
Duration of wait for dial tone =02 seconds
Duration of wait for carrier after dialing =30 seconds
Duration of dial pulse (comma)=02 seconds
Carrier detect response time =0.1 seconds
Escape code guard time =1 second
Length of use after comma =2.0 seconds
Last carrier to hang up delay =0.1 seconds
DTMF interdigit delay =0.1 seconds
Sleep mode inactivity time = off
Long space disconnect disabled
V.22B selected
Factory Pre-Configuration. Cermetek pre-configures
the CH1786A modems with the following command
set:
Enter: AT+MS=V22B,1,300,2400,300,2400<CR>
Result: OK
Enter:
ATS0=1%C0&C1&D0&S1&Q6\N0&Y0&W0<CR>
Result: OK
IMPORTANT NOTE
If the AT&F, AT&F0 or AT&F1 commands are
executed by the user, the Factory Pre-configuration
commands specified above must be executed after
the AT&F, AT&F0 or AT&F1 commands to ensure
proper configuration setup of the CH1786A
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 16 Document No. 607-0019 Revision A8 (03/06)
Figure 6. PSTN Line Interface for all CH1786A Products. CH1786AL and CH1786AN models do NOT
contain internal Surge Protection (Dashed Box 2). The purchaser MUST be provide external
surge protection to maintain conveyed FCC Part 68 approval.
1. Current Limiting PSTN Protection Line Device.
Current limiting devices are mandatory to meet UL
safety standards. To maintain conveyed FCC Part
68 approval, the current limiting components
identified as F1 and F2 in dashed Box 1 must also
survive FCC Part 68 surge testing. Refer to
Cermetek Application Note #126, Supplemental
PSTN Line Protection, for more details. Refer to
Application Note # 130, Summary of Recommend
Suppliers, for a list of suppliers and associated part
numbers.
A resettable/repairable fuse (rated at 0.15 amps) is
preferred because it resets automatically upon
removal of the current flow. Non-resettable devices
are also acceptable. Although CS-03 Part 1
(Canada) follows the requirements of FCC Part 68
(USA), Cermetek recommends contacting a
certified independent lab to verify compliance in the
specific application.
2. Over Voltage and Lightning Protection.
Surge Protection is provided by internal circuitry
contained within all CH1786A models except
CH1786AL and CH1786AN. No additional external
components are required to maintain conveyed
FCC Part 68 approval for all models EXCEPT
CH1786AL and CH1786AN.
For CH1786AL and CH1786AN, the required surge
protection (identified as D1 in Dashed Box 2) must
be supplied externally. The purchaser must include
some form of surge protection as described herein
to maintain conveyed FCC Part 68 approval. Refer
to Application Note # 130 for a list of suppliers.
3. Optional External Over Voltage and Lightning
Protection.
In most environments, the internal two terminal
surge suppressor (see dashed Box 3) is adequate.
For severe environments, use an external three
terminal device with an earth ground as is shown in
dashed Box 3.
4. EMI/RFI Suppression.
Suppression of emitted EMI/RFI is recommended
and is typically required to obtain FCC part 15 A
and/or B approval. EMI/RFI suppression circuitry is
also used to suppress reception of externally
generated EMI/RFI signals, such as strong radio
signals, should the CH1786A be located near a
source of such signals. Although no external
EMI/RFI noise suppression circuitry is required to
maintain conveyed FCC Part 68 approval,
additional suppression may be added as described
below without adversely affecting FCC Part 68
approval.
A. To provide adequate EMI/RFI suppression, the
capacitor/inductor network contained in dashed
Box 5 should be located as close to the RJ-11C
Jack as possible. Further, this network should
be provided with an excellent ground path to the
chassis.
B. Capacitors C1 and C2 should not exceed
0.005µf. They must have a rating of 1.5KV and
typically are 0.001µf ± 20%. Inductors L1 and
L2 may be either individual inductors or a dual
inductor. Refer to Application Note #130 for a
list of suppliers. For UL applications, choose
capacitors and inductors that are UL 1950
Edition 3 listed. The actual values of the
components used may vary depending on the
end product design and the nature of the EMI/
RFI. Consult an FCC Part 15 consultant, if
required.
All models except
CH1786AL and CH1786AN
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 17 Document No. 607-0019 Revision A8 (03/06)
Table 7. CH1786A System Data Mode Compatibility Specifications.
Parameter Specification Parameter Specification
Asynchronous 2400, 1200 600 bps character
asynchronous.
0-300 bps asynchronous
Receive Carrier
Frequencies
V.22 bis, V.22,
212A
Originate 2400Hz ± 7Hz
Answer 1200Hz ± 7Hz
Asynchronous Speed
Range
TXD may differ +1%, -2.5%
from modem output. Offsets
will be corrected by adding/
deleting stop bits.
Bell 103 Answer ‘space’ 2020Hz ±
7Hz
Answer ‘mark’ 2225Hz ±
7Hz
Originate ’space’ 1070Hz ±
7Hz
Originate ‘mark’ 1270Hz ±
7Hz
Asynchronous Format 8,9,10 bits, including start,
stop, parity.
Receiver
Sensitivity
OFF to ON threshold –43
dBm
ON to OFF threshold –48
dBm
Telephone Line Interface Two-wire full duplex over
public switched network. On-
chip hybrid and billing delay
timers.
Billing Delay 2.0 to 3.0 seconds (Ta=25°C)
Modulation V.22 bis, 16 point QAM at 600
baud. V.22 and 212A, 4 point
DPSK at 600 baud. 103
Binary phase coherent FSK.
Hysteresis 2 dB minimum
Self Test Pattern
Generator
Alternate ‘ones’ and ‘zeros’
and error detector, to be used
along with most loopbacks. A
number indicating the bit
errors detected is sent to DTE.
Line
Equalization
Fixed compromise
equalization, transmit.
Adaptive equalizer for
PSK/QAM, receive.
Transmit Carrier
Frequencies V.22 bis,
V.22, 212A
Originate 1200Hz ± .01%
Answer 2400Hz ± .01%
Diagnostic
Available
Local analog loopback. &T1
Local analog loopback.
Must be used with error
correction off (AT&Q6).
Bell 103 Originate ’space’ 1070Hz ±
.01%
Originate ‘mark’ 1270Hz ±
.01%
Answer ‘space’ 2025Hz ±
.01%
Answer ‘mark’ 2225Hz ±
.01%
Call Progress
Tones Detected
Computer
Interface
With speaker or quiet screen
messages (No dial tone,
busy, ring, modem answer
tone and voice).
IBX PC/XT/AT bus
compatible with an
8250/16450/16550A UART
as a serial controller.
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 18 Document No. 607-0019 Revision A8 (03/06)
Table 8. CH1786A Electrical Specifications.
Parameter Description Min. Typ. Max. Units
VCC Positive Supply Voltage- Noise less than 50mV 4.75 5.0 5.25 V
ICC Off Hook Nominal Operating Current when modem is OFF Hook 61 67 mA
ICC On Hook Nominal Operating Current when modem is ON Hook 58 64 mA
ICCPD Power Down Current @
VCC = 5.5V when modem is in Power Down Mode2
0.0 mA
IRIPD Current Supplied into RI pin when in Power Down
Mode @ VCC = 5.5V2
11.0 uA
VIH High Level Input Voltage1 2 Vcc+.
5
V
VIL Low Level Input Voltage1 0 0.8 V
IIN Input Leakage Current (TXD, DTR, RTS) -10 +10 uA
ILO Leakage Current DCD, HS, RXD, SLEEP, DSR -10 +10 uA
VT+ Positive Hysteresis Threshold for RESET pin 3.0 V
VT- Negative Hysteresis Threshold for RESET pin 1.33 V
VOH High Level Output Voltage (IOH = 2.0mA)1 2.4 V
VOL Low Level (IOL = - 2.0mA)1 0.4 V
Test conditions: VCC = 5V ± 10%, Temp = 0°C to 70°F (unless otherwise stated).
Notes:
1. Output Load = 50 pF ± one TTL.
2. With recommended 30k ohm external resistor. Maximum external resistor range: 10k to 100k ohm.
Table 9. CH1786A Electrical Specifications.
Parameter Minimum Typical Maximum Units Comments
DC Off Hook Impedance 125 312 Ohms @16 to 80 ma
Trans Hybrid Loss 25 dB 600 Ohm, RXA, TXA
Ring Voltage Detect 25VAC 35VAC VRMS Typically riding on 48VDC
Line Loop Current-
(Off-Hook)
16 80 mA
Return Loss @ 1000Hz 15 dB 600 Ohm
Ring Detect Frequencies 14 20 35 Hz
Receiver Insertion Gain -0.5 0.0 +0.5 dBm 600 Ohm- Data Mode
Transmit Power
(Adjustable with S91)
-17.2 -13.0 -9.5 dBm Into 600 Ohm Load
First Character After Reset 0.5 1.0 5 sec Delay
Inter Character Delay 20 50 msec Between all command
characters
Command Delay 100 200 msec Between all AT commands
Maximum Reset Drive 0 10K Ohms
Minimum Reset Pulse
Duration
10 msec If user supplied
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 19 Document No. 607-0019 Revision A8 (03/06)
Table 10. Other Performance Specifications.
Parameter Minimum Typical Maximum Units Comments
DTMF total power -5.3 -5.6 --5.8 dBm Into 600 ohm load
DTMF Twist (Balance) 2 3 dB
DTMF Tone Duration 50 85 255 ms 85ms default
Pulse Dialing Rate 8 10 20 pps 10pps default
Pulse Dialing Make/
Break
39/61 % US, Canada default
Pulse Interdigit Interval 700 3000 ms 789ms default
Guard Tone Frequency 1800 Hz Referenced to High Channel
Transmit
Guard Tone Amplitude -9 dB Referenced to High Channel
Transmit
High Channel Transmit
Amplitude
-1 dB Referenced to Low channel,
Guard tone enabled
Guard Tone 2nd
Harmonic Distortion
-40 dB
Call Progress
Passband Frequency
205 720 Hz @ -20 dBm received tone
Wait Time for Dial tone 2 255 sec Two second default
Return loss @ 1000Hz 15 dB Tr=600Ω
Table 11. Analog Characteristics.
Name Type Characteristic Value
SPK O(DF) Minimum Load
Maximum Capacitive Load
Output voltage
300Ω
0.01µ
1.65± .6V
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 20 Document No. 607-0019 Revision A8 (03/06)
Table 12. CH1786A Pin Functions.
PACKAGE CONNECTION TABLE
PIN NO. FUNCTION PIN NO. FUNCTION
1 RING 12 V/D
2 TIP 13 DTR
3 RXA 14 DSR
4 TXA 15 RI
5 SPK 16 CTS
6 NC 17 DCD
7 NC 18 NC
8 SLEEP 19 VCC
9 NC 20 GND
10 TXD 21 RST
11 RXD 22 NC
Figure 7. CH1786A Physical Dimensions.
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 21 Document No. 607-0019 Revision A8 (03/06)
Table 13A. Summary CH1786A Family of Non-RoHS Compliant Products.
Model Summary of Features Operating Temperature
CH1786A Full Function, 2400bps, FCC Part 68 Approved, UL 1950 Listed 0°C to + 70°C
CH1786A-C Full Function with Caller ID (CID), 2400bps, FCC Part 68
Approved, UL 1950 Listed
0°C to + 70°C
CH1786A-L Full Function, 2400bps, FCC Part 68 Approved, UL 1950 Listed,
No EEPROM, No Internal Surge Protection
0°C to + 70°C
CH1786A-N Full Function, 2400bps, FCC Part 68 Approved, UL 1950 Listed,
No EEPROM, No Internal Surge Protection, No 2-4 Wire
Converter Circuit (i.e., No Voice Inject Capability)
0°C to + 70°C
CH1786A-P Full Function with Zero Power Down, 2400bps, FCC Part 68
Approved, UL 1950 Listed
0°C to + 70°C
CH1786A-CP Full Function with Caller ID (CID) and Zero Power Down,
2400bps, FCC Part 68 Approved, UL 1950 Listed
0°C to + 70°C
CH1786A ET Full Function, 2400bps, FCC Part 68 Approved, UL 1950 Listed -40°C to +85°C
CH1786A ET-C Full Function with Caller ID (CID), 2400bps, FCC Part 68
Approved, UL 1950 Listed
-40°C to +85°C
CH1786A ET-P Full Function with Zero Power Down, 14.4kbps, FCC Part 68
Approved, UL 1950 Listed
-40°C to +85°C
CH1786A ET-CP Full Function with Caller ID (CID) and Zero Power Down,
2400bps, FCC Part 68 Approved, UL 1950 Listed
-40°C to +85°C
Table 13B. Summary CH1786A Family of RoHS Compliant Products.
Model Summary of Features Operating Temperature
CH1786AR Full Function, 2400bps, FCC Part 68 Approved, UL 1950 Listed 0°C to + 70°C
CH1786AR-C Full Function with Caller ID (CID), 2400bps, FCC Part 68
Approved, UL 1950 Listed
0°C to + 70°C
CH1786AR-L Full Function, 2400bps, FCC Part 68 Approved, UL 1950 Listed,
No EEPROM, No Internal Surge Protection
0°C to + 70°C
CH1786AR-N Full Function, 2400bps, FCC Part 68 Approved, UL 1950 Listed,
No EEPROM, No Internal Surge Protection, No 2-4 Wire
Converter Circuit (i.e., No Voice Inject Capability)
0°C to + 70°C
CH1786AR-P Full Function with Zero Power Down, 2400bps, FCC Part 68
Approved, UL 1950 Listed
0°C to + 70°C
CH1786AR-CP Full Function with Caller ID (CID) and Zero Power Down,
2400bps, FCC Part 68 Approved, UL 1950 Listed
0°C to + 70°C
CH1786AR ET Full Function, 2400bps, FCC Part 68 Approved, UL 1950 Listed -40°C to +85°C
CH1786AR ET-C Full Function with Caller ID (CID), 2400bps, FCC Part 68
Approved, UL 1950 Listed
-40°C to +85°C
CH1786AR ET-P Full Function with Zero Power Down, 2400bps, FCC Part 68
Approved, UL 1950 Listed
-40°C to +85°C
CH1786AR ET-CP Full Function with Caller ID (CID) and Zero Power Down,
2400bps, FCC Part 68 Approved, UL 1950 Listed
-40°C to +85°C
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 22 Document No. 607-0019 Revision A8 (03/06)
ATTACHMENT I
Page 1 of 2
Table 14. Cross Compatibility Comparison Chart.
Old (non “A”) Model Equivalent New Model Comments
CH1786 CH1786A Standard CH1786A. No Options needed.
CH1786LC CH1786A-L No EEPROM, No Internal Surge Protection.
CH1786ET/PD CH1786A-ET
or
CH1786A ET-P
Standard extended temp CH1786A. No
options needed if Power Down not required.
Standard extended temp CH1786A with
Power Down option.
CH1786NH CH1786A-N No EEPROM, No Internal Surge Protection,
No 2-4 wire circuitry (i.e., No voice inject
capability).
Table 15. Summary of differences between CH1786 and CH1786A products.
ITEM CH1786 CH1786A
PIN CONFIGURATION
PIN 18 HS. LOW indicates 2400bps operation. Not Supported. No Connect.
IDENTIFICATION COMMANDS
ATI0. Product Code. 242 14400
ATI1. ROM Checksum. 192 042
ATI2. Checksum
Verification.
OK OK
ATI3. Identify current
firmware code.
AFES-C2501-H0 CX81802-V32
MODEM OPERATION COMMANDS
Long Space Disconnect. ATYn command supports:
n=0 Disables long space disconnect
(default).
n=1 Enables long space disconnect.
Not Supported.
On-Line Echo Character. ATFn command supports:
n=0 Returns ERROR result code.
n=1 Returns OK result code (default).
Not Supported.
Test and Diagnostic. AT&Tn command supports:
n=0 Terminates test in progress.
n=1 Initiates Analog loopback.
n=2 Returns ERROR.
n=3 Initiates local Digital loopback.
n=4 Enables Digital loopback
acknowledgement from remote RDL.
n=5 Disables Digital loopback
acknowledgement from remote RDL.
n=6 Initiates remote Digital loopback.
n=7 Initiates remote Digital loopback
with self test.
n=8 Initiates local Analog loopback
with self test.
AT&Tn command supports:
n=0 Terminates test in progress.
n=1 Initiates Analog loopback.
n=2-8 Not Supported.
NOTE: The identification code returned when the I0, I1, I3 commands are executed may vary, depending on
manufacture date.
Cermetek Microelectronics, Inc. CH1786A Family of Ultra Small 2400bps Modems
2006 Cermetek Microelectronics, Inc. Page 23 Document No. 607-0019 Revision A8 (03/06)
ATTACHMENT I
Page 2 of 2
Table 14. Summary of differences between CH1786 and CH1786A products (Continued).
ITEM CH1786 CH1786A
FAX OPERATION COMMANDS
Flow Control. AT+FF command supports:
n=0 Disable enhanced flow
control (default). EIA-578 standard.
n=1 Enables enhanced flow
control.
AT+FLO command supports:
n=0 XON/XOFF and RTS/CTS flow control turned off
(default).
n=1 XON/XOFF flow control on in both directions.
n=2 Use RTS for flow control of modem by DTE; use CTS
flow control of DTE by modem.
Transmit Test Data. +FTTn=m command. Not Supported.
Receive Test Data. +FRTn command. Not Supported.
NVRAM
Stored Telephone
Number Length
36 digits (maximum) 31 digits (maximum)
STORED PARAMETERS
Retrieval of factory
default profiles.
Execute AT&F or AT&F1 to retrieve
Firmware Default setup parameters.
Execute AT&F, AT&F0 or AT&F1 to retrieve Firmware
Default setup parameters. To restore the CH1786A to the
CH1786 default configuration, the following commands
MUST be executed after executing the AT&F, AT&F0 or
AT&F1 commands:
Enter: AT+MS=V22B,1,300,2400,300,2400<CR>
Result: OK
Enter: ATS0=1%C0&C1&D0&S1&Q6\N0&Y0&W0<CR>
Result: OK
Cermetek reserves the right to make changes in specifications at any time and without notice. The information furnished by
Cermetek in this publication is believed to be accurate and reliable. However, Cermetek assumes no responsibility for its use, or for
any infringements of patents or other rights of third parties resulting from its use. No license is granted under any patents or patent
rights of Cermetek.
Cermetek provides the user with a FCC (USA) and IC (Canada) Approved or device. However, Cermetek does not have influence
over nor knowledge of the specific user application environment. Therefore, for FCC and IC Approved or Approvable devices, the
user assumes all risk for maintaining compliance to registration.
Printed in U.S.A
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