Datasheet CH1787ET, CH1787 Datasheet (CRMET)

CH1787

Small Footprint Hardware Controllable 2400bps Modem

INTRODUCTION FEATURES

The CH1787 is a small footprint, full function 2400bps,
V.22bis asynchronous modem designed to be used in
applications where there is little or no external controller
intelligence to command the modem. The CH1787
allows the user to operate the modem via hardware
resources only, not requiring AT command execution
for basic operation. For those applications where an
external controller is available, the CH1787 operates
like a standard AT Command driven modem.

• Supports Standards CCITT V.22bis, V.22, Bell 212,

and Bell 103

• FCC Part 68 approved and DOC approvable

• Does not require a microprocessor to operate

• Pin activated hang-up

• Pin activated answer

• Manual originate and answer pins

• AT Command structure available

• UL1459 Recognized

• 1000 VAC isolation barrier, 1500V peak isolation

• Single 5 volt operation The CH1787 is ideal for use as a remote modem in

applications such as alarm products and in industrial
controllers. The CH1787 will dial a pre-stored
telephone number under pin activation control to make
a connection with another modem. The CH1787 can
also answer incoming calls (either automatically or
manually) using the ANS pin. A call is terminated by
activating the HNG pin.

• Low power sleep mode

• Automatic adaptive and fixed compromise

equalization

• Test modes and diagnostics

• Size: 2.0” X 1.25” X 0.53”

• NVRAM allows storage of custom configurations

and telephone numbers

• Commercial operating temperature: 0° to 70°C

• Extended temperature: –40° to 85°C (CH1787ET)

GENERAL DESCRIPTION OF FUNCTIONAL
BLOCKS

Figure 1 contains a functional block diagram of the
CH1787. The CH1787 is comprised of a
modulator/demodulator, controller, an FCC Part 68
approved telephone interface Data Access
Arrangement (DAA) and NVRAM.

Modulation/Demodulation and Control. This
functional Block is comprised of a monolithic modem
integrated circuit, with built-in facilities to accommodate
integrated AT command control and resident interfaces
for general communication and routing to the DAA.

Controller. The controller is a programmed
microprocessor that provides commands to the modem
in response to external pin activation. The following
pins are controlled by the microprocessor and are
described in detail in Table 1. These pins are
operational when the modem is in use at 2400bps only.

ANS Manual Answer Pin Input – Answer mode –

Places modem in answer mode

Figure 1. CH1787 Functional Block Diagram.

ORG Manual Originate Pin Input – Originate

mode – Places modem in originate mode

DAA. The CH1787 is designed to meet North
American telephone standards as set by FCC Part 68
and DOC. The telephone line interface meets UL1459
with 1000VAC and 1500 volt peak surge isolation. As
such, it complies with U.S., Canadian, and other
international requirements that specify that level of
isolation. The CH1787 is FCC Part 68 pre-approval. A
label is provided with the registration number and ringer
equivalent (REN). This label should be prominently
displayed on the host equipment. As with most

ORA Automatic Dial Pin Input – Dials one of two

pre-stored numbers based on TST

HNG Forces CH1787 to disconnect
AAR Enables Auto Answer
TST Selects phone number to be dialed. Works

with ORA

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Cermetek Microelectronics, Inc. CH1787 Small Footprint Hardware Controllable 2400bps Modem

countries (except the U.S.), Canada requires
submission of the product containing the CH1787 for
DOC approval. This can be done by submitting the
design to a test house or consultant. Call Cermetek for
assistance.

NVRAM. NVRAM can save a maximum of four
telephone numbers with up to 36 digits or modifiers in
each. The AT&Zn=s command will store s, the
telephone number dial string. The ATDTS=n command
will cause the CH1787 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. Location 1 is used for the ORA stored numbers
and Cermetek number. The AT&Wn command will
store the active 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 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 2 and
3 for storable S-Registers and Commands.

SUPPORTED FEATURES

AT Command Set. A 40-character command line is

supported. The command line starts with AT and may
contain standard or enhanced commands. See the
Cermetek website at

http://www.cermetek.com for

publication AT Commands and S-Registers.

Serial Host Interface. The serial interface is V.24
(EIA-232-D) compatible. See pin description in Table

1.

Speaker Interface. The SPK output reflects the
receiver analog input and provides a signal that can be
used to monitor call progress. Although the SPK signal
can drive a 300 load directly, the SPK signal is usually
input to an audio power amplifier and the amplifier
drives a speaker coil. Figure 5 shows how to drive an
8 speaker.

The speaker can be turned on and off with the ATMn
command. The speaker volume can be adjusted by the

ATLn command, where n is 0, 1, 2 or 3.

Phone Control. The Voice/Data (V/D) pin toggles high

when the modem goes off hook and can be used to
activate a relay which can switch a telephone on or off
the TIP and RING Telco lines. This feature allows the
telephone to be disconnected when a data call is in
progress, preventing the data from being disturbed by
an inadvertent telephone pick-up. See Figure 2.

SLEEP MODE

Sleep Mode is a power down feature designed to
minimize power consumption. When activated, the

CH1787 will automatically enter Sleep Mode after a
user specified period of inactivity. The inactivity
counter increments in whole seconds and is selected
by the ATS24 command. The default is 0 seconds.
The modem returns to normal operation when a ring
signal is received or upon an input low signal on TXD.

ATS24 = 255 disables Sleep Mode.

Figure 2. Voice/Data Port Control.

A SLEEP output signal is available to control power to
external devices. In Figure 5, a FET controlled by the
SLEEP signal turns off the external speaker amplifier
when the modem enters the Sleep Mode. Sleep Mode
reduces power consumption by approximately 50%.

Transmission Speed. The CH1787 can be either
originating (calling modem) or answering (remote
modem).The transmission rate of the host computer
must be 300, 1200, or 2400bps. The CH1787 will
connect at the selected speed or will fall back to the
speed set by the remote or answering modem (the DTE
transmission speed). The following table indicates the
speeds:

Originate

Speed

Connect Speed Based on Answer

Speed of:

300 1200 2400*

300 300 300 300
1200 300 1200 1200
2400 300 1200 2400

*Pin activated operation at 2400bps only. Other
speeds may be used with AT Command operation.

Speed and Parity Selection. Before a call, the
modem adjusts to the host speed (2400, 1200, or
300bps) and parity (odd, even, mark, space, or none)
via a host-initiated training sequence. This also selects
the speed of the data for originate calls. The CH1787
automatically adapts to the caller’s speed on answer
calls.

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The CH1787 matches the host’s parity when it returns
status messages to the host. During a data connection,
however, the CH1787 passes parity through without
interpretation or alteration.

POWER SUPPLY

The CH1787 module is a complex sub-system that may
be treated as any other component. Special attention
should be paid to the power supply connections. The
CH1787 decodes analog signals from the telephone
line that are in the millivolt range. All though the
CH1787 is designed to withstand significantly induced
power supply noise, there is a limit. Steps must be
taken to guarantee that power supply noise on all
supply lines, including ground, does not exceed 50 mV
peak to peak. Any frequency between 20kHz and 150
kHz must be less than 50 mV peak. If necessary, use
dedicated power and ground planes. Failure to provide
such operating conditions could cause the CH1787 to
malfunction.

Figure 3. Voice/Tone Injection.

Training the Modem. The modem must be trained to

match the host’s speed and parity so that it is able to
recognize serial asynchronous commands sent to it by
the host UART. The host must retrain the modem each
time a reset signal is applied on RST or after a RESET
serial command. The modem is trained by sending it
the following three-character sequence.

The CH1787 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 is recommended that a 10µF Electrolytic
capacitor in parallel with a 0.01µF ceramic capacitor be
used.

Enter: AT<CR>

IMPORTANT NOTE
The CH1787 has been FCC Part 68 approved as a
data modem. Utilization of the Voice/Tone Port
requires further registration. FCC will require that
the system, including the CH1787 and the handset
or DTMF transceiver, adhere to Part 68 rules.

Where: A and T must be upper case or lower
case <CR> represents carriage return

The modem will respond with one of the following
status messages, depending on whether it is optioned
for abbreviated (terse) or English (verbose) status
messages.

Response: 0<CR> terse

<CR><LF>OK<CR><LF> verbose

MODEM CONTROL

The CH1787 may be controlled by sending serial
ASCII command sequences on TXD (Pin 16). After
execution of the command, the CH1787 returns a
serial status message on RXD (Pin 31).

Where: <CR> represents carriage return (ASCII 13)
<LF> represents line feed (ASCII 13)

The CH1787 may be retrained at any time when in idle.

Initializing the Modem. Before commands may be
sent to the CH1787, the modem must be initialized.
This consists of two events: 1) after power-up, a
hardware reset pulse must be applied to the modem,
and 2) the modem must be trained to the host’s speed
(2400, 1200, 300bps) and parity (odd, even, mark,
space or none).

Another attention sequence A/ is much like the AT
sequence except it repeats the previously entered
command specified with an AT prefix. When given, it
must also be in upper case ASCII. No carriage return
is needed.

THE COMMAND FORMAT

Power-up Reset. After applying power to the modem,

an internally generated reset pulse is created. The
user can also reset the modem externally by applying a
high-going reset pulse to RST for at least 10ms after
the +5V power supply has stabilized. Delay sending
commands to CH1787 for 100-200ms after power up.

Typical commands consist of three elements: the
attention sequence, the commands themselves, and a
terminating carriage return.

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Figure 4. CH1787 Application Diagram of Test Circuit.

Table 1. CH1787 Pin Descriptions.

PIN NAME I/O FUNCTION

1 RING I/O RING. Directly connects to the telephone line’s RING lead through a user’s supplied RJ-11C

jack.
2 TIP I/O TIP. Directly connects to the telephone line’s TIP lead through a user’s supplied RJ-11C jack.
7 RXA O ANALOG VOICE INJECT. Transit and receive analog voice signal. Let float if not used.
8 DTR I DATA TERMINAL READY input. Active LOW. Switching off a DTR can either return modem

to command state, disconnect phone call, or reset modem. DTR should be set LOW when not

used.
9 ANS I ANS. Used to manually answer an incoming call. Input has two modes of operation

depending on its state during reset. When ANS is low during reset, the CH1787 will go off

hook in the answer mode and send an answer tone continuously waiting for an originating

tone. This mode of operation is used on a dedicated non dial-up telephone line (leased line).

When ANS is high during reset, the modem will initiate an answer tone whenever the ANS Pin

goes low during normal operation. The modem will send the answer tone for 30 seconds and

then stop. The CH1787 will then repeat the answer tone sequence as long as ANS is low.
10 V/D O VOICE/DATA. Used to switch between telephone and modem line use. When low, the

modem is in the control mode and a voice circuit can be switched out, RXA, TXA when high

the modem is in the data mode and the input should be TXD/TXD.
11 RST1 I RESET (active high). Must be asserted HIGH for at least 10ms to reset the modem. RESET is

then returned LOW for normal operation. If no system reset is available, let this pin float to

enable internal reset.
12 RI O RING INDICATION. This signal follows the frequency of the ringing signal which is typically 20

to 40 Hz for 2 seconds on and 4 seconds off.

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Table 1. CH1787 Pin Descriptions (Continuation).

13 CTS - CLEAR TO SEND. Active LOW. Output always low. Indicates CH1787 is ready to accept

data from DTE.
14 DSR O DATA SET READY. LOW indicates handshaking with a remote modem is in progress, and/or

the data carrier of a remote modem is detected.
15 ORA I ORA (active low). When LOW, CH1787 will dial one of two stored telephone numbers

depending on the status of the TST pin. The numbers are programmed using the AT&ZO

command. A pre-stored number is provided to allow testing. It is in permanent loop back

answering on the second ring. The CH1787 will make up 15 attempts to connect with the

stored number at 60 second intervals as long as ORA is low. DCD low indicates a successful

connection. If ORA goes high, no further attempts to connect will be made. If, after

disconnecting from a valid connection, ORA is low the CH1787 will be unresponsive until ORA

is first placed high then low. The FCC requires that automatic dialing attempts not exceed 15

to the same number.
16 TXD I TRANSMIT DATA. Serial receive data input. Marking or a binary 1 condition is transmitted

when a HIGH is asserted.
17 DIR O DIR indicates when the TXD and RXD lines are used for internal CH1787 connection. When

DIR is high, valid data is on RXD and TXD. When DIR is low, the user may ignore RXD data

and should not place any data on TXD since it will be ignored by the CH1787. The user should

monitor this pin or gate it as shown in Figure 4 to prevent data from begin erroneously

interpreted by the user’s host processor.
18 IRQ - 4.7KW resistor to 5V.
19 SLEEP O SLEEP. A LOW indicates modem is in low power idle mode. Used to control power to other

devices. See Figure 5. When the modem is inactive for a period of time specified by register

S24, the CH1787 will power down to about 50% of its normal operating power. I/O Lines will

become undefined. The factory set default for the CH1787 is sleep mode is inhibited

(S24=255).
20 GND I GROUND.
21 DCD O DATA CARRIER DETECT. LOW indicates that a data carrier from a remote modem has been

detected. DCD follows carrier is the default.
22 HS O SPEED INDICATION. A LOW on this pin indicates the modem is operating at 2400bps.
23 ORG I ORIGINATE (active LOW) places CH1787 in off hook mode without dialing. Used to originate

a connection on dedicated leased lines (i.e.,”dry” lines). The remote modem must be in

answering mode.
24 N/C - No connection.
25 N/C - No connection.
26 N/C - No connection.
27 SPK O SPEAKER. Audio Output. See Figure 5.
28 TST I Test pin input used in conjunction with ORA to steer the dialing between a user stored number

(TST LOW) and a pre-stored Cermetek test number (TST HIGH). See ORA description.
29 CON O CON indicates a valid 2400bps connection. May be used in place of DCD and HS to start the

communications or to indicate the start of an exchange of data.
30 HNG I HNG (active LOW). Used to force the CH1787 to disconnect. The HNG pin is only functional

when DCD is active (LOW).
31 RXD O RECEIVE DATA. Serial receive data output. Received MARKING or a binary 1 condition is

indicated by a HIGH.
32 VCC I 5 volts ± 5%. Note: Noise should be less than 50mV
33 GND I GROUND.
34 AAR I AAR (active LOW). When asserted low then high, CH1787 will auto answer during a RING

cycle. AAR can be tied low primarily to enable Auto Answer on the first RING. AAR will not

override auto answer condition e.g., S0  1.

Spare pins are available for custom functions. Contact Cermetek with your requirements.

Note: (1) If VCC has a slow power up ramp time, the internal reset may be ineffective.

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AT [commands] <CR>. Where <CR> represents
carriage return (ASCII 13). When entering commands
to the CH1787, the backspace character CTL H (ASCII

8) can be used to edit mistakes. AT and A/ may not be
edited. Multiple commands may concatenated on a
single command line. Command lines may not exceed
40 characters, excluding AT. The command string
below instructs the CH1787 to train itself, to not echo
characters in the command mode E0 and then go to the
answer mode A.

Enter: ATE0A<CR>
Response: OK <CR><LF>

AT COMMAND DATA RATE

With the serial interface, the rate is speed sensed for
parity and format.

AT COMMAND SET

The command set is divided into three types as listed in
Table 2: basic commands, dial modifiers and
ampersand commands.

THE STATUS MESSAGES

The CH1787 responds with a status message after
each command is executed. This status message may
either be a single digit followed by a carriage return or a
carriage return and line feed with a message in English,
followed by a carriage return and line feed.

The basic status code subsets are enabled with the Xn
command. Where n=0,1,2,3,5 the status codes can be
in message form or result codes selected for the five
Xn commands.

X0 – Result Codes 0, 1, 2, 3, 4
X1 – Result Codes 0, 1, 2, 3, 4, 5, 10
X2 – Result Codes 0, 1, 2, 3, 4, 5, 6, 10
X3 – Result Codes 0, 1, 2, 3, 4, 5, 7, 10
X4 – Result Codes 0, 1, 2, 3, 4, 5, 6, 7, 10 (factory

default)

Modem States. The CH1787 may be in either the
Command mode or the Data Mode. When the CH1787
is idle, it is in Command Mode by default. When a data
transmission is in progress, the CH1787 is in Data
Mode and will not recognize commands. The host
system must send an “escape sequence” to the
CH1787 forcing it out of the Data Mode and into the
Command Mode before commands will be accepted.

Escape Sequence. The escape sequence consists of
a guard time (a period where no characters are sent to
the CH1787) followed by 3 escape characters, followed
by a guard time. At power-up, the guard time is set to 1
second (minimum), and the escape character is set as

“+.” These parameters can be modified via registers S2
and S12, respectively.

The CH1787 will stay off-hook with its carrier on after
the escape sequence is received. It returns an OK
status message when it is ready to accept commands.
The data mode is reentered by issuing the ATO
command.

Result Status

Messages

Meaning

0 OK Command executed.
1 Connect Carrier detected at

300bps.
2 Ring Ring detected.
3 No Carrier Did not detect carrier.
4 Error Entry error.
5 Connect 1200 Carrier detected at

1200bps.
6 No Dial Tone Off-hook, but no response

after 5 seconds.
7 Busy Busy signal detected.

10 Connect 2400 Carrier detected at

2400bps.

Dial Modifiers Function

P Pulse Dial
R Originate Call in Answer

Mode

T Touch Tone Dial

W Wait for Dial Tone

; Return to Idle State

@ Wait for Quiet Answer

Command
! Flash Hook
, Pause

0-9/ A,B,C,D Dial Digits/Characters

AT COMMAND APPLICATIONS
Dial A Number. The Dial command takes the form

Dn, where n is a string of characters. In the simplest

form, n will only the digits of the phone number to be
dialed.

Example: Dial number

Enter: AT D 1234567<CR>

In response to this command, the CH1787 dials the
telephone number “123-4567” and then waits for the
carrier from the remote modem. If no carrier is
detected within a given time (the default time is 30
seconds), the CH1787 automatically releases the line
and sends a NO CARRIER result code. If a carrier is
detected, the CH1787 issues a CONNECT result code
and goes on-line, permitting communication with the
remote modem.

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The Dial Command may also be issued without a
telephone number. The ATD command causes the
modem to pick up the telephone line without dialing a
number.

Table 2. CH1787 Register Summary.

Register Function

S0* Ring to Answer On

S1 Ring Count
S2 Escape Code Character
S3 Carriage Return Character
S4 Line Feed Character
S5 Back Space Character
S6 Wait for Dial Tone
S7 Wait Time for Data Carrier
S8 Pause Time for Comma

S9 Carrier Detect Response Time
S10 Lost Carrier to Hang-up Delay
S11 DTMF Dialing Speed
S12 Escape Code Guard Time

S14* Bit Mapped options Register

S16 Modem test Options

S18* Test Timer
S21* Bit Mapped options Register
S22* Bit Mapped options Register
S23* Bit Mapped options Register

S24 Sleep Mode Inactivity Time

S25* Delay to DTR
S27* Bit Mapped options Register

S28* Bit Mapped options Register
*= S-Register stored in NVRAM upon receipt or & W
command.

Using the Pause Character. 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 directs the CH1787 to pause for a
specific length of time. The factory default pause time
is 2 seconds.

Example: Dial 9, pause, and dial number.

Enter: ATDT9,1234567<CR>
Response: Dial tone, DTMF tone generation

Multiple commas may be used to increase delay time.

TOUCH TONE AND PULSE DIALING

The CH1787 can use DTMF (touch-tones) or dial
pulses when dialing a telephone number. If the dial
command does not specify which type to use, the
CH1787 defaults to the type last specified. The power­on default value is P.

Example: Pulse dial 9, pause, and touch-tone dial
number.

Enter: ATDT9,1234567;
Response: Dial tone, DTMF tones, return to Command

State
Enter: ATDP9T1234567<CR>
Response: Dial tone, Pulse dialing

S0 DO NOT ANSWER TELEPHONE
S1 ANSWER ON RING 1

Originate a Call in Answer Mode. The D command

forces the CH1787 into originate mode. To call an
originate-only modem, dial the number and set the
modem to answer mode via the R (reverse originate).
Enter the R command at the end of the telephone
number.

S2 ANSWER ON RING 2
S3 ANSWER ON RING 3

When S0 is set to 0, the modem will not auto-answer.

Example: assign the value 6 to S0 to set the CH1787

to answer on the sixth ring.
Redial Last Number. Use A/, the repeat command, to
redial the last telephone number dialed when a busy
signal is received.

Enter: ATS0=6<CR>

Response: OK

Return to Command State. The CH1787 can be
forced to reenter the command state after dialing
(without hanging up) by ending the dial command with
a semicolon. This is useful when using the CH1787 as
an auto dialer.

CONNECTING TO THE HOST UART

Since the CH1787 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.

Automatic Answering. The S0 register controls the
number of rings that must occur before the modem
answers a call. The register may range in value from 0-

255.

The Serial Interface Lines. The CH1787 supports the

full RS-232C/V.24 serial interface. Signal levels are

TTL rather than RS-232C level compatible, which

allows the user to directly connect the CH1787 to the

host’s UART without needing level translating circuitry.
Example: Touch-tone dial 9, pause, dial number,

return for command.

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Table 3. CH1787 AT Command Set Summary.

Basic

Commands Function

AT Attention Code

A Answer Command

A/ Repeat Last Command

*Bn Communications Standard Option

D Dial Command

*E Off-Line Character Echo Option

Hn Switch Hook Control Option

*Ln Speaker Volume Option

*Mn Speaker Control Option

On On-Lone Command

P Pulse Dial

*Qn Result Code Display Option

Sn Select an S Register
Sn= Write to an S Register
Sn? Read an S Register

*Vn Result Code From Option
*Xn Result Code Set/Call Progress Option

+++ Escape Code Sequence

, Pause

? Returns Last Addressed S Register

*Yn Long Space Disconnect Option

Fn On-Line Echo Character Option

Z Reset

Ampersand
Commands Function

*&Dn Data Terminal Ready Option

&F Load Factory Defaults

*&Gn Guard Tone Option
*&Pn Make to Break Ratio Selection
*&Sn Data Set Ready Option

&Tn Test Command Option

&V View Active Configuration

*&Wn Store Active Profile

*Yn Recall Active Profile
*&Zn Store Telephone Numbers
*&Cn Not Supported

Percent

Commands Function

%Dn DTMF Attenuation

%J Load Secondary Factory Defaults

*= Commands that can be stored in NVRAM.

NOTE: Refer to Cermetek Publication AT Commands

and S-Registers for a detailed discussion of
parameters in Table 2 and 3.

Two of these lines are all that are required for proper
CH1787 operation: TXD, RXD and DTR. The modem
is controlled by sending it serial commands over TXD
and can be monitored by serial status messages
returned on RXD.

All other serial interface lines may be utilized for the
convenience of your application but are not required by
the modem. Unused outputs (form modem) should be

left unconnected. Unused inputs should be tied to the
proper logic level. See pin description.

Figure 5. Speaker Control. Circuit allows call

progress monitoring.

PHONE LINE CONNECTION GUIDELINES

1. The mounting of CH1787 in the final assembly
must be made so 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 CH1787 to the telephone line
interface must be provided in wiring that carries no
other circuitry than that specifically allowed in the
rules (such as A and A1 leads).

3. Connection to phone line should be made through
an RJ-11 jack.

4. Traces from the modem’s RING and TIP pins to the
RJ-11 jack must exceed 0.1 inch spacing to one
another and 0.2 inch spacing to all other traces.
The traces should have a nominal width of 0.020
inches or greater.

5. The RING and TIP traces should be as short as
possible and oriented to prevent coupling other
high speed or high frequency signals onto the host
circuit card.

6. No additional circuitry other than that shown in the
following Figure may be connected between the
modem module and RJ-11 jack.

7. The CH1787, the RJ-11 jack, the interfacing
circuitry and traces in between, must be mounted
on a circuit board with a 94 V-0 flammability rating.

8. The supplied FCC registration label must be
applied visibly on the outside of the host product.

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Type of Service: The (insert your 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
FJ45S). Connection to telephone-company-provided
coin service (central office implemented systems) is
prohibited. Connection to party lines service (central
office implemented systems) is prohibited. Connection
to party lines service is subject to state tariffs.

9. The host product’s User Manual must provide the
user with instructions for connection and use as
recommended in Section FCC Registration.

MOUNTING THE MODEM

The modem contains static-sensitive devices and
should only be handled by personnel and in areas that
are properly protected against static discharge.

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, the telephone company will give you notice,
in writing, to allow you to make any changes necessary
to maintain uninterrupted service.

There are two mounting techniques that are
recommended for physically connecting the modem to
your circuit card; 1) sockets, and 2) direct soldering.

The socking approach to mounting eliminates cleaning
and desoldering concerns. When the socket is used, it
must make a solid connection to all modem pins.
Failure to do so will cause unreliable modem operation.
Also, steps should be taken to assure that the module
remains tightly seated in the socket after the host
product is shipped.

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 advance notice is
not feasible, you will 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
telephone company if you have any questions about
your phone line.

FCC REGISTRATION

The CH1787 is 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 product that contains the
modem of several restrictions the FCC places on the
end user of the product that contains the modem and
its use. The following notice is recommended and
should be included in the host product’s USER
MANUAL. Also, the FCC requires that Cermetek make
all repairs to the modem. If repair is necessary after
the modem is installed in your product and has been
delivered to your customer, the modem must be
returned to you where it can be removed from the host
product and the forwarded to Cermetek for repair.

In the event repairs are ever needed on the (insert your
product name), they should be preformed by (insert
your company name) or an authorized representative of
(insert your company name). For information contact:
(insert your company address).

FOR YOUR USER’S MANUAL

FCC Part 68 rules require the following (or equivalent)
information be provided to the end user of equipment
containing a DAA.

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, Subpart 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
suchspecifications and/or inspections will be provided
by the FCC within 30 days of their request for the
same.

2002 Cermetek Microelectronics, Inc. Page 9 Document No. 607-0002 Revision B (03/02)

Cermetek Microelectronics, Inc. CH1787 Small Footprint Hardware Controllable 2400bps Modem

PSTN PROTECTION REQUIREMENTS

B. In most environments, 2 terminal surge

suppressors are adequate. For severe
environments, use an external 3 terminal
device with an earth ground.

1. Currently Limiting PSTN Protection Line Device.

Currently 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.

3. EMI/RFI Suppression.

No external EMI/RFI noise suppression circuitry is
required to maintain conveyed FCC Part 68
approval. However, additional suppression, if
required for other reasons, may be added as
described below in Sections 3A-3B without
adversely affecting FCC Part 68 approval.

A. A PTC (rated at 0.15 amps) is preferred

because it resets automatically upon removal of
the current flow. Non-resettable devices are
also acceptable. Refer to Application Note
#130 for a complete list of recommended
vendors and associated part numbers.

A. To provide adequate EMI/RFI suppression, the

capacitor/inductor network contained in dashed
Box #3 should be located as close to the RJ11
Jack as possible. Further, this network should
be provided with an excellent ground path to
the chassis.

B. Resistors (10 carbon film or 1/8 watt

minimum) may be used in Canada, as Canada
has no requirements that PSTN equipment be
operational after a Type B surge test.

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
complete list of recommended vendors and
associated part numbers. For UL applications,
choose capacitors and inductors that are UL
1950 listed. The actual values of the
components used may vary depending on the
end product design.

C. Although CSA CS-03 Part 1 (Canada) follows

the requirements of FCC Part 68 (USA),
Cermetek recommends contacting DOT
(Canada) and/or a certified independent lab to
verify compliance. For Canada, use either 10
resistors (carbon film or SMD parts 1/8 watt
minimum) as described in paragraph B above.

2. Over Voltage and Lightning Protection.

A. Surge Protection is provided by internal

circuitry (see Figure 3). No additional external
components are required to maintain conveyed
FCC Part 68 approval.

Figure 6. Telephone Interfaces.

2002 Cermetek Microelectronics, Inc. Page 10 Document No. 607-0002 Revision B (03/02)

Cermetek Microelectronics, Inc. CH1787 Small Footprint Hardware Controllable 2400bps Modem

Default Status, Performance, and Specs Default
Configuration Profile

Async mode selected
2400bps
Bell 212A operation at 1200bps
Even parity
Auto answer disabled
Command echo ON
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 medium
Local modem will grant RDL request from remote
modem
Guard tones disabled
Minimum DTR pulse width = 0.1 seconds
Ring count – 01 (CH1786)
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 deal 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
DTMF Attenuation = -4dB
Sleep mode inactivity time = 5 seconds
Long space disconnect disabled

2002 Cermetek Microelectronics, Inc. Page 11 Document No. 607-0002 Revision B (03/02)

Cermetek Microelectronics, Inc. CH1787 Small Footprint Hardware Controllable 2400bps Modem

Table 4. CH1787 System Data Mode Compatibility Specifications.

Parameter Specification Parameter Specification

Asynchronous 2400, 1200, 600bps character

asynchronous. 0-300bps
asynchronous

Receive Carrier

Frequencies

V.22bis, V.22, 212A

Originate+HZ 2400Hz +7Hz
Answer 1200Hz +7Hz

Asynchronous

Speed Range

TxD may differ +1%, -25% from
modem output. Offsets will be
corrected by adding/deleting stop
bits.

Bell 103 Answer ‘space’ 2025Hz +7Hz

Answer ‘mark’ 2225Hz +7Hz
Originate ‘space’ 1070Hz +7Hz
Originate ‘mark’ 1370Hz +7Hz

Asynchronous

Format

8, 9, 10bits, including start, stop,
parity

Receiver Sensitivity OFF to ON threshold -43 dam

On to OFF threshold -48 dam

Telephone Line

Interface

Two-wire full duplex over public
switched network. On-chip hybrid
and billing delay timers.

Modulation V.22bis, 16 point QAM at

600baud. V.22 and 2212A, 4
point, DPSK at 600baud. 103
binary phase coherent FSK.

Hysteresis 2dB minimum

Self Test Pattern

Generator

A

lternate ‘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.22bis, V.22,

212A

Originate 1200Hz +.01%
Answer 2400Hz +.01%

Diagnostics

Available

Local analog loopback.
Local digital loopback.
Request remote digital loopback.
Local interface loopback modem
with self-test.

Bell 103 mode 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-back, modem answer tone
and voice).

IBM PX/XT/AT bus compatible
with an 8250/16450/16550A
UART as a serial controller.

2002 Cermetek Microelectronics, Inc. Page 12 Document No. 607-0002 Revision B (03/02)

Cermetek Microelectronics, Inc. CH1787 Small Footprint Hardware Controllable 2400bps Modem

Table 5. CH1787 Electrical Specifications.

Ta=25°C

Symbol Characteristic Min. Typ. Max. Units

VCC Supply voltage 4.75 5.0 5.25 V

ICC Supply Current

Off hook operating current
On hook operating current
Power down operating current

50
40
16

75

mA
mA
mA

VOL Output Low voltage

(I

OL

=0.4mA) CON
(IOL=5.0mA) DIR
(IOL=1.6mA) SLEEP, DSR, DCD, HS, RXD
(I

OL

=4mA) V/D

0.3

0.3

0.4

0.26

V
V
V
V

VOH Output High Voltage

(IOH=0.2mA) CON, DIR
(IHL=-100uA) SLEEP, DSR, DCD, HS, RXD
(IOL=0.4mA) V/D

4.45

2.4

4.18

V
V
V

VIL Input Low Voltage

TST, ORG, ORA, HNG, AAR, ANS
DTR, TXD

0.95

0.8

V
V

VIH Input High Voltage

TST, ORG, ORA, HNG, AAR, ANS
DTR, TXD

3.3

2.4

V
V

VT+ Positive Hysteresis Thresold for Reset Pin 2.7 V

VT- Negative Hysteresis Thresold for Reset Pin 1.6 V

Table 6. CH1787 Electrical Specifications.

Parameter Minimum Typical Maximum Units Comments

Ring Voltage Loop 40 VRMS
Return Loss @ 1000 Hz 17 dB 600
Ring Frequencies 15.3 68 Hz
Transmit Level -11 dBm 600 – Data Mode
Command Mode After Reset 5 sec Delay
Inter Character Delay 20 msec Between all command characters
Command Delay 100 msec Between all AT commands
Minimum Reset Pulse 5 msec If user supplied

Table 7. Other Performance Specifications.

Parameter Minimum Typical Maximum Units Comments

DTMF Twist (Balance) 3 dB
DTMF Tone Duration 50 255 ms 95ms default
Pulse Dialing Rate 10 20 pps 10pps default
Pulse Dialing Make/Break 39/61 % US, Canada default
Pulse Dialing Make/Break 33/67 % UK, Hong Kong
Pulse Interdigit Interval 700 3000 ms 789ms default
Call Progress Passband Frequency 120 620 Hz
Wait Time for Dial Tone 2 255 sec Two second default

Table 8. Product Family Summary.

Model Feature Summary Operating Temperature

CH1787 FCC Part 68 Approved, UL1459 Registered 0°C to +70°C

CH1787ET FCC Part 68 Approved, UL1459 Registered -40°C to +85°C

2002 Cermetek Microelectronics, Inc. Page 13 Document No. 607-0002 Revision B (03/02)

Cermetek Microelectronics, Inc. CH1787 Small Footprint Hardware Controllable 2400bps Modem

2002 Cermetek Microelectronics, Inc. Page 14 Document No. 607-0002 Revision B (03/02)

Figure 7. CH1787 Physical Dimensions and Pin Functions.

Package Connection Table

Pin No. Function Pin No. Function

1 RING 18 IRQ
2 TIP 19 SLEEP
3 NOT POPULATED 20 GND
4 NOT POPULATED 21 DCD
5 NOT POPULATED 22 HS
6 NOT POPULATED 23 ORG
7 RXA 24 N/C
8 DTR 25 N/C

9 ANS 26 N/C
10 V/D 27 SPK
11 RST 28 TST
12 RI 29 CON
13 CTS 30 HNG
14 DSR 31 RXD
15 ORA 32 VCC
16 TXD 33 GND
17 DIR 34 AAR

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, no responsibility is assumed by Cermetek 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.

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