CH1788
Surface Mount PLCC 2400bps Modem
INTRODUCTION
The CH1788 modem has the smallest footprint and
lowest profile of any commercially available full
function, FCC Part 68 approved 2400bps modem.
Utilizing a 68 pin PLCC form factor and requiring a
minimum amount of PCB space (0.95”x0.95”x
0.255”), the CH1788 affords the design engineer
and 300bps.
maximum flexibility.
The CH1788 provides two
external interfaces: a ITU-T V.24 standard 5 volt
serial interface for routing directly to a UART; and a
TIP and RING interface for connection to the PSTN
telephone line.
The CH1788 is compatible with
support with external circuitry.
available industry communication software or may be
controlled with software commands via an embedded
microcontroller.
CH1788.
The
CH1788
modem
supports
asynchronous
operation at 2400bps, 1200bps, and 300bps to both
Bell and ITU-T standards.
Each device is FCC
power idle and zero power standby modes.
approved and Canadian DOT approvable. An FCC
label is supplied. The CH1788 also meets UL 1950
Edition 3 requirements.
standard 68 pin PLCC socket.
The CH1788 family of modems operate from a 5 volt
DC supply (3.3 volt devices are available by special
order). The combination of low power operation, zero
power standby mode and small form factor make the
CH1788 FAMILY
CH1788 an ideal choice for portable equipment
CH1788
Operating Temperature:
0 ° C to +70 ° C
CH1788ET
Operating Temperature:
-40 ° C to +85 ° C
CH1788-3
3.3 volt Operation
Operating Temperature:
0 ° C to +70 ° C
CH1788-3ET
3.3 volt Operation
Operating Temperature:
-40 ° C to +85 ° C
DESCRIPTION OF FUNCTIONAL BLOCKS
applications.
AND DISCUSSION OF BASIC OPERATIONS
Figure 1 contains a functional block drawing of the
CH1788. The CH1788 is a highly integrated, full-
Figure 1. Functional Block Diagram of CH1788.
function
modem,
comprised
of
a
modulator/
demodulator, controller, and an FCC Part 68
approved telephone line interface.
FEATURES
Modulation/Demodulation and Modem Controller.
Bell 212, and Bell 103, Bell 202, V.23.
This function is provided by a monolithic modem
integrated circuit. The function is performed to ITU-T
standards thereby making the CH1788 compatible
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CH1788 Surface Mount PLCC 2400bps Modem
with all modems.
The ability to execute AT
the data connection DCE speed will be equivalent to
commands is consistent with industry standards.
the originating modems serial connection DTE speed.
In other words, disabling Speed Buffering forces the
Telephone Line Interface or DAA. The CH1788 is
answering modem to connect with a DCE speed
designed to meet 1500VAC RMS isolation and
equivalent to the serial DTE speed of the originating
provide 2122V peak surge protection. Consequently,
modem.
the CH1788 satisfies North American and some
international requirements. Note that supplemental
Data Transmission Speed. The CH1788 allows the
protection is required for FCC Part 68 conveyed
DTE speed to be set to 300, 1200, 2400, or 9600bps.
approval (see Figure 3 of this document).
This
The DCE speed can be set to 2400, 1200, or 300bps.
supplemental protection also improves field reliability
A connect message will appear on RXD indicating the
and facilitates FCC part 15 approval.
connected data rate.
General Operation.
By definition, the originating
SUPPORTED FEATURES
modem initiates the PSTN connection and the
AT Command Set. Internal to the CH1788 is an AT
answering modem accepts the incoming call. The
command interpreter.
AT commands and their
connectivity speed (i.e., DCE speed) is determined by
associated S-registers provide macro functionality.
the originating modem.
These commands are summarized in this document
and are detailed in Cermetek publication CH1788 AT
The originating modem’s DTE speed is established,
Command and S-Register Reference Guide.
in turn, with an initializing AT command issued by the
application’s host controller. Speed Buffering allows
The CH1788 supports command concatenation. A
the CH1788 to communicate with the host controller
maximum of 63 characters (excluding AT ) may be
at a DTE speed that is greater than the connect DCE
included on each command line. S-registers provide
speed.
added programmability by allowing key parameters to
be configured for a specific application.
Assuming that the default configuration of the
CH1788 has not been modified with the ATB or ATY0
Serial Host Interface.
The serial interface is a
commands, the answering modem will attempt to
standard TTL V.24 5V DC interface. It is functionally
connect to the originating modem at the highest
similar to an RS232 interface.
possible data rate supported by the originating
modem. The connection rate can be less than the
IMPORTANT NOTE
maximum of 2400bps, for example, if the PSTN line is
Do not use RS232 interface voltage levels on the
impaired in some way.
serial pins. Damage may result. Adhere to the TTL
V.24 5V DC interface standard. See Schematic 7
By default upon power up, the CH1788 DTE speed is
for a suggested circuit to interface RS-232 logic to
set to 9600bps and Speed Buffering is enabled.
the CH1788 TTL V.24 logic.
Typical
Implementation.
In
a
typical
implementation, the CH1788 has a DTE speed of
Command Characters. Each data byte or command
9600bps and will connect to the remote modem at a
character consists of ten bits: 1 start bit, 1 stop bit,
DCE speed of 2400bps. Speed Buffering allows the
and eight data bits. The data bits can be either eight
CH1788 to negotiate the DCE speed independent of
bits with no parity or seven odd or even with 1 parity
the DTE speed. Data transfer to the host will be at
bit. The start bit is LOW going. RXD and TXD data is
the DTE Speed Buffered rate of 9600bps. In this
non-inverted. See the pin descriptions in Table 2.
case, flow control is not required.
Data Encoding.
The data encoding is user
It is possible for the DTE speed to be slower than the
configurable. The ATB command sets the decoding.
DCE speed.
For example, a serial interface DTE
The following ITU-T standards are supported:
speed of 1200 bps and a data rate DCE speed of
V.22bis, V.22, Bell 212A, 103, Bell 202 or V.23.
2400 bps.
In this case, flow control must be
employed by the host to prevent buffer overflow and
Speed Buffered Mode. Speed Buffering allows the
lost data.
serial data interface or DTE speed (i.e., the speed
between the host microcontroller and the CH1788) to
be fixed regardless of the connect or DCE speed (i.e.,
the speed between the CH1788 and the remote
POWER DOWN
modem).
The CH1788 has two power down modes: idle power
standby and zero power standby.
The option exists to disable Speed Buffering by using
the ATY0 command. If Speed Buffering is disabled,
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CH1788 Surface Mount PLCC 2400bps Modem
Idle Power Standby. In idle power standby mode is
including ground, does not exceed 50 mV peak to
enabled by executing ATS73+2 in the set up string.
peak. Any frequency between 20 kHz and 150 kHz
Power is switched off automatically by the CH1788
must be less than 500 micro volts peak. If necessary,
after a period of no activity and is restored
use dedicated power and ground planes. Failure to
automatically by the CH1788 when activity is again
provide such operating conditions could cause the
detected. Activity is defined as a change of status on
CH1788 to malfunction or to function erratically.
DTR, TXD, RST or on any of the other input pins or
an Incoming Ringing signal on TIP/RING. Idle power
Recommendation. To reduce the effects of supply
mode transitions are transparent to the user.
noise, it is recommended that by-pass capacitors be
placed on the power supply as close to the CH1788’s
Zero Power Standby. In applications requiring near
supply input (i.e., Pin 20) as practical.
A 10 µ F
zero power during standby periods, the power may be
Tantalum capacitor in parallel with a 0.01 µF ceramic
switched completely off to the CH1788. This is done
is recommended.
by issuing the AT@Z command or by toggling DTR
after the ATR5 command has been executed.
Normal operation is resumed by performing a 50
DTMF TONE DETECTION
msec (minimum) hardware reset on the RST pin.
The CH1788 is capable of detecting DTMF tones
without external hardware.
RING INDICATION
Setup. Detection will only occur when the CH1788 is
The CH1788 produces a low going 80 msec pulse on
Off-Hook and in the command mode.
the RI Pin when a valid Incoming Ring signal is
detected.
By default, a valid ring signal must fall
DTMF Decoding.
The ATJ6 command enables
within the 10-75 Hz range and have a cadence of 2
DTMF decoding.
Register S65 will contain the
seconds on and 4 seconds off. Alternate frequency
decoded DTMF result.
The S65 register must be
ranges and ring cadence’s may be programmed.
continuously interrogated by the host controller
because the decoded DTMF decimal value is only
present in S65 when the DTMF tones are present on
CH1788 RESET
the PSTN line.
The CH1788 may be reset using any of the following
methods. Delay sending commands to the CH1788
The full range of decoded DTMF decimal values are
for a period of 500 msec after reset has been
listed in Table 1. If the S65 register contains zero, it
completed to allow the CH1788 time to properly
indicates that no DTMF tones are present. Note, the
reconfigure.
S65 register will contain zero between DTMF tones.
Hardware Reset. Upon power-up or when power
Recommendation. Sample the S65 register at a
cycling, the CH1788 will automatically generate an
rate at least twice (2X) the fastest DTMF tone
internal reset pulse. However, if the power supply
periodic rate. DTMF tones typically have a cadence
comes up too slowly, or has a rise time greater than
of 70 msec on and 70 msec off. In this case, the S65
50 msec, the internal reset detection circuitry may not
register should be sampled at least every 35 msec.
generate the hardware reset.
Table 1. DTMF Tone Conversion.
RST Pin. Initiate a reset externally anytime after the
DTMF TONE
DECIMAL VALUE
power supply has stabilized by applying a 50 msec
1
129
TTL high reset pulse to the RST pin.
2
130
Software Reset. Execute the ATZ command while in
3
131
command mode.
4
132
DTR Pin. Toggle the DTR pin after executing the
5
133
ATR3 command while in command mode.
6
134
7
135
POWER SUPPLY
8
136
Although any standard 5 volt DC supply is
9
137
acceptable, the user should be aware that during the
0
138
course of normal operation the CH1788 decodes
*
139
analog data signals from the PSTN line that are in the
millivolt range. Steps must be taken by the user to
#
140
insure that power supply noise on all supply lines,
No Tone
0
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CH1788 Surface Mount PLCC 2400bps Modem
DTMF TONE GENERATION
Setup. The LIU feature requires additional external
The CH1788 is capable of generating DTMF tones
circuitry.
See Schematic 5 and Schematic 6.
without external hardware. DTMF tone generation is
Additionally, register S110 must be set to 243.
useful for signaling and is supplemental to the DTMF
dialing capability.
PARALLEL PICK-UP
The Parallel Pick-Up (i.e., PIU) feature allows the
Setup. Generation will only occur when the CH1788
termination of a CH1788 modem call in progress, and
is Off-Hook, in the command mode and prior to
then allows a standard phone instrument sharing the
carrier generation.
same PSTN line to seize the line and obtain a dial
tone. When terminating the modem call, DCD will go
DTMF Encoding. By default, the CH1788 generates
high, if enabled. The PPU-V status message appears
DTMF tones at a 70 msec on/off cycle. The cycle can
on RXD.
be modified with register S11.
Setup. The Parallel Pick-Up feature requires external
Issuing an ATDT command string with the desired
circuitry. See Schematic 5.
DTMF digits and terminating the command string with
a semicolon ( ; ) will cause the CH1788 to immediately
Operation. The Parallel Pick-Up circuit detects the
enter command mode after dialing. Alternatively, the
incremental change in Off-Hook voltage on the PSTN
command mode may be entered from the data mode
line. If a parallel connected phone instrument is Off-
by issuing the escape sequence ( +++ ) to the
Hook, the CH1788 will not attempt to go Off-Hook. If
CH1788.
the CH1788 is already Off-Hook and a parallel
connected phone instrument goes Off-Hook, the
Enter:
ATDT1234567890*#;<CR>
CH1788 will terminate the calling progress and allow
Result:
Sends the DTMF tones and returns to
the sharing device to seize the line.
command mode.
DO not exceed 63
characters on the command line.
Failure To Detect.
The detection circuit in the
CH1788 may not detect the Off-Hook condition for
DTMF Tones may also be sent using external
select phone instruments because some phone
circuitry via the voice injection port. See Schematic
instruments may not change the Off-Hook voltage
2.
sufficiently to allow detection.
There is also the possibility that two devices going
CALLER ID
Off-Hook simultaneously may defeat the PPU
The CH1788 will detect Caller ID (i.e., CID)
detection circuitry.
information. CID data, when supplied by the local
telephone service provider, is present between the
Recommendation.
To avoid a Failure To Detect
first and second ring signals.
Valid CID data is
condition, use of a prioritized scheme such as that
preceded by the “CID” designation. This feature is
employed in the 911 Priority Pick-Up application
enabled via register S95.
circuit described below is strongly suggested.
Setup. CID requires additional external circuitry. An
IMPORTANT NOTE
RC network must be added to the CH1788 V+ and V-
The Parallel Pick-Up feature should only be used in
pins.
See Schematic 4 for details.
Register S95
non-critical applications and never used as a
must be set to 8 (the default value) to receive the CID
substitute for the 911 Priority Pick-Up feature.
information.
Other caller ID options are available.
See the details of register S95.
911 PRIORITY PICK-UP
Operation. Using the circuit in Schematic 4, monitor
The 911 Priority Pick-Up (i.e., 911 PPU) feature
the RI pin for the period between the first and second
allows the CH1788 to give Off-Hook priority to any
ring signal. The decoded CID data will appear on
telephone sharing the PSTN line with the CH1788.
RXD.
Setup.
The 911 Priority Pick-Up feature requires
external circuitry. See Schematic 6.
LINE IN USE
The Line In Use (i.e., LIU) feature allows the CH1788
Operation. If a parallel connected phone instrument
to signal the host when a shared PSTN line is in use.
goes Off-Hook while the CH1788 is Off-Hook, the
When in use, the LINE IN USE status message will
CH1788 will immediately disconnect to give priority to
appear on RXD and the CH1788 will NOT go Off-
the phone instrument.
Hook. This feature is enabled via register S110.
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CH1788 Surface Mount PLCC 2400bps Modem
CH1788
Top View
1
Used for LIU/911/General IO
22
2
A1
RXD
DTE Signal
Used for LIU/911/Audio Control
21
OH
GND
Power Input +5V
DTE Signal
3
RTS
V CC
20
DTE Signal
4
RI
S2
19
Optional S1/S2 Audio
DTE Signal
5
CTS
S1
18
Monitor/Tone/Voice
DTE Signal
6
DSR
DTE Signal
7
DCD
15
DTE Signal
8
DTR
V-
14
V+/V- Optional
Used for LIU/Detection
9
A2
V+
CID Input
DTE Signal
10
TXD
TIP
13
Telephone Line
Optional High Reset Input
11
RST
RING
12
Input
High Voltage Section
Figure 2. CH1788 Pin Configuration. See Table 2 for detailed Pin Descriptions.
Table 2.
CH1788 Pin Descriptions.
PIN
NAME
TYPE
FUNCTION
1
A1
O
Optional Input. Active high. Used when implementing the 911 Priority Pick-Up
circuit or the Line In Use circuit.
2
OH
O
Off-Hook. Active low. OH Indicates when the CH1788 is Off-Hook. Used in Line
In Use, 911 Priority Pick-Up applications and for Audio Control.
3
RTS
I
Request To Send . Active low. Used for optional flow control. Used in conjunction
with the Clear to Send (CTS) pin as a handshaking signal. See the details of
register S90.
4
RI
O
Ring Indication. Active low. For each occurrence of a valid ring signal, this pin will
pulse low for 70 ms. This output signal follows the frequency of the ringing signal
and is typically in the 20 to 40 Hz range with a cadence of 2 seconds on with 4
seconds off.
5
CTS
O
Clear to send. Active low. Used for optional flow control. Used in conjunction with
the Request To Send (RTS) pin as a handshaking signal.
6
DSR
O
Data Set Ready.
Active low. A low indicates that handshaking with the remote
modem is in progress and/or the carrier of the remote modem has been detected
and a valid connection is imminent as measured by DCD being active. This feature
is enabled with the N command.
7
DCD
O
Data Carrier Detect. Active low. This output must be enabled with the ATC1
command. When enabled, it will become active when both the originated and
answering modems are connected and a data carrier has been detected.
NOTE:
1. All unused pins should be left unconnected when not required in a specific application,
unless specifically directed otherwise.
2. See DC characteristics before attempting to drive an LED directly from the output of any pin.
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CH1788 Surface Mount PLCC 2400bps Modem
Table 2.
CH1788 Pin Descriptions (Continued).
PIN
NAME
TYPE
FUNCTION
8
DTR
I
Data Terminal Ready. Active low. The response to this input is controlled by the
Rn command where n specifies the desired options and includes: returning the
modem to the command state, hanging up the modem, resetting the modem, and
placing the modem in zero power mode.
9
A2
I
Optional Input. Active low. Used when implementing the Line In Use circuit.
10
TXD
I
Transmit Data. Serial transmit data input. Data starts with a high to low transition.
Mark or binary 1 condition is indicated by HIGH.
11
RST
I
Reset. Active HIGH. This input must be asserted HIGH for at least 50 ms to reset
the modem.
The RST pin must be returned LOW for normal operation to
commence. If a system reset is not available, let this pin float to enable the internal
reset circuitry.
12
RING
I/O
Ring. Telephone connection requires an active public switched telephone line
(PSTN) for normal operation. This line should be routed to the RJ-11C jack through
the recommended protection circuitry.
13
TIP
I/O
TIP.
Telephone connection requires an active public switched telephone line
(PSTN) for normal operation. This line should be routed to the RJ-11C jack through
the recommended protection circuitry.
14
V+
I
Caller ID. Used to connect an external RC network to enable caller ID operation.
See the application circuit in the Schematic 4.
15
V-
I
Caller ID. Used to connect an external RC network to enable caller ID operation.
See the application circuit in the Schematic 4.
18
S1
I/O
Audio Port. Optional audio port input. Allows the internal DAA to be shared with
external voice, tone injection or call progress monitoring applications. See the
application circuits in the Schematic 2 and 3.
Note that the CH1788 is FCC
approved for data applications only. Inclusion of voice or other audio functions may
require additional certification by the FCC.
19
S2
I/O
Audio Port. Optional audio port input. Allows the internal DAA to be shared with
external voice, tone injection or call progress monitoring applications. See the
application circuits in the Schematic 2 and 3.
Note that the CH1788 is FCC
approved for data applications only. Inclusion of voice or other audio functions may
require additional certification by the FCC.
20
V CC
--
Power Supply. 5 Volt DC +/- 5%. Supply noise should be less than 50 mV pp . Also
available at for 3.3 volt DC operation, upon special request.
21
GND
-
Ground. Circuit ground. Use recommended bypass capacitors between GND and
VCC.
22
RXD
O
Receive Data. Serial receive data output. Data starts with a high to low transition.
Received mark or binary 1 condition is indicated by HIGH.
NOTE:
1. All unused pins should be left unconnected when not required in a specific application,
unless specifically directed otherwise.
2. See DC characteristics before attempting to drive an LED directly from the output of any pin.
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CH1788 Surface Mount PLCC 2400bps Modem
IMPORTANT NOTE
IMPORTANT NOTE
The 911 PPU feature requires the CH1788 must be
The Fast Connect feature is operational only for DTE
the first device on the installation’s PSTN line. All
speeds of 1200bps (Bell 212).
other phone or higher priority instruments to be
down the line from the CH1788.
LONG SPACE DISCONNECT
The long space disconnect signal is used to force the
CALL PROGRESS MONITORING
CH1788 to release the PSTN line and go back On-
Call Progress Monitoring allows a call to be monitored
Hook.
during the dialing sequence. This feature becomes
active when the CH1788 goes Off-Hook and
Setup. To enable this feature, bit 7 of register S110
automatically disables when DCD is detected. It is
most be set to 1. See the details of register S110.
also inactive if a connection attempt should fail and
the CH1788 goes back On-Hook.
To enable this
feature, the DCD line must be activated with the
VOICE INJECTION
ATC1 command.
It is possible to share the CH1788’s internal DAA with
external applications. This allows one PSTN line to
Setup.
This feature requires additional external
be shared between an external voice application and
circuitry. See Schematic 2. Although the circuit in
the CH1788 modem. This feature is controlled via
Schematic 2 uses a variable resistor to adjust the
register S101 when using the configuration in
speaker volume, a fixed value resistor may be
Schematic 3.
substituted.
Setup.
This feature requires additional external
Alternate Setup.
Control of the speaker can
circuitry.
See Schematic 3.
This application
alternately be performed under command control. To
implements Voice Injection via the S1 and S2 pins
implement this alternate control method, modify the
and requires a two to four wire converter and a relay
circuit in Schematic 2 by connecting resistor R5 to A1
circuit. Set S101 to 1 to activate Voice Inject and set
instead of DCD. This allows register S101 to be used
S101 to 0 to deactivate Voice Inject.
to turn the speaker on or off. Set S101 to 1 to turn
the circuit on, set S101 to 0 to turn the circuit off.
Operation. The two to four wire converter circuit
provides for simultaneous voice in and voice out (with
respect to ground). This circuit must be capacitor
FAST CONNECT HANDSHAKING
coupled (i.e., C7) to the CH1788 and isolated from
The CH1788 supports a fast handshaking (often
ground (i.e., C6). Voice/data switching is controlled
called “quick connect”) feature.
by setting register S101 appropriately.
Typically, the initial handshaking sequence for a V.90
During Voice Injection, the voice signal must not
modem (56Kbp) takes 20-30 seconds to complete. A
exceed 2.187 V pp (i.e., zero dB) per FCC maximum
standard 2400bps (V.22bis) modem connects in 4-8
permissible limits.
When sending data, the voice
seconds. With the Fast Connect feature enabled, the
circuit must be fully disconnected from the line (i.e.,
CH1788 will connect at 1200bps (Bell 212) in as little
Voice Inject deactivated) or data corruption will occur.
as 0.5 seconds.
This feature will work with any
compatible modem.
IMPORTANT NOTE
Setup: Originate Mode. The Fast Connect feature,
When utilizing the Voice Injection circuit, it is
when the CH1788 is in originate mode, is activated by
necessary to submit the end product containing the
using the following command setup string:
CH1788 Voice Injection feature to an FCC approved
testing facility for re-approval of the end product per
Enter: ATFY0X4K0S30=$10S89=$40<CR>
FCC Part 68 requirements.
Result: OK
Setup: Answer Mode. The Fast Connect feature,
MODEM CONTROL
when the CH1788 is in answer mode, is activated by
The CH1788 may be controlled with ASCII AT
using the following command setup string:
commands sequences. The commands are sent to
the CH1788 serially via the TXD pin. After execution
Enter: ATL3<CR>
of a received command string, the CH1788 returns a
Result: OK
serial status message on RXD.
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CH1788 Surface Mount PLCC 2400bps Modem
Where: A and T may be either upper or lower case
INITIALIZING THE MODEM
but must be the same case.
The CH1788 must be initialized before the CH1788
<CR> represents carriage return
will recognize commands. Initialization is a two step
The AT sequence is referred to as the attention
activity consisting of:
sequence. When received, the CH1788 will respond
with one of the following status messages, depending
Table 4.
Hard Reset. This is accomplished by
on whether the CH1788 is optioned for Terse
applying a hardware reset pulse to
(abbreviated) or Verbose (English) status messages.
pin RST for 50 ms.
The internal
reset may be used by cycling the
Result:
0<CR>
(Terse)
power. The modem should not be
or
accessed for 500 msec after a reset
Result:
<CR><LF>OK<CR><LF> (Verbose)
has occurred.
Where:
<CR> represents carriage return (ASCII 13
or HEX 0D).
<LF> represents line feed (ASCII 10 or
IMPORTANT NOTE
HEX 0A).
Delay the sending commands to the CH1788 for a
period of 500 msec after reset has been completed
After responding, the CH1788 will be in command
to allow the CH1788 time to properly reconfigure.
mode and ready to accept additional commands. An
alternate attention sequence A/ may be sent. This
command causes the previously entered command
string specified with the AT prefix to be executed.
2. Initial CH1788 Training.
This will establish the
word bit length and type for communication with
the host. The word size should not be more than
AT Command Set. The available commands are
10 bits including start and stop bits and is typically:
summarized in Table 5. Note that each command
1 start bit, 1 stop bit, 8 data bits and with no parity.
may have several options and the options may be
The CH1788 is trained by the host with the
influenced by various S-Register values.
It is
AT<CR> .
The serial data rate (i.e., the DTE
recommended that the designer review Cermetek
speed) at which the host sends the AT<CR>
publication CH1788 AT Commands and S-Registers
command initializes the modem DTE Speed.
Reference Guide.
3. The CH1788 S registers must be re-configured to
AT Command Structure. When issuing commands
their required settings after a soft reset, hardware
to the CH1788, the backspace character-control-H
reset, or power loss.
(ASCII 8 or HEX 08) may be used to perform
character editing.
Multiple commands may be placed on the command
THE COMMAND FORMAT
line as long as the command line does not exceed 63
Typical commands consist of three elements: the
characters, excluding the letters AT .
By way of
attention sequence, the commands themselves, and
example, the command string below instructs the
a terminating carriage return.
CH1788 to configure itself to suppress character
echoing when in command mode E0 and then put
AT[commands]<CR>.
itself in the answer state A .
Where: AT represents attention sequence.
[Commands] represents command strings.
Enter: ATE0A<CR>
<CR> represents carriage return (ASCII 13
Result: OK
or HEX 0D).
Training the Modem. The CH1788 must be trained
IMPORTANT NOTE
to set the DTE speed (i.e., to match its host’s speed
Allow a minimum of 125msec delay between
and parity) so that the CH1788 is able to recognize
subsequent AT commands.
serial asynchronous commands sent to it by the
host’s UART. The host must retrain the CH1788
each time a reset is performed.
MODEM STATES
The CH1788 is in either of two states: command
Modem Training Command Sequence.
The
mode or data mode. The CH1788 will only respond
CH1788 is trained by sending it the AT sequence:
to AT commands when it is in command mode.
When the modem is idle, by default it is in command
Enter: AT<CR>
mode.
Result: OK
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
When data transmission is in progress, the CH1788 is
in this state, the CH1788 will not receive data from
in data mode and will not recognize/respond to AT
the remote modem.
commands.
To cause the CH1788 to recognize
Result Codes. After execution of an AT command
commands when in data mode, the host must send
and at the completion of each dial attempt, the
an escape sequence to the CH1788 forcing the
CH1788 will deliver a status message on RXD.
CH1788 out of data mode and into command mode.
Referring to Table 3, the message can be a Terse
Only then will the CH1788 respond to AT commands.
(numeric) or Verbose (English) message.
The
message type is controlled via the V command.
If the CH1788 is Off-Hook, connected to a remote
Various combinations of the listed result codes can
modem and placed in command mode by its host, the
be selected with the W and X commands.
CH1788 will not transmit any commands received
from its host to the remote modem. However, when
Table 3.
Summary of Common Result Codes and Meanings.
Standard Result Codes
Terse
Verbose
Meaning/Description
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
8
NO ANSWER
Remote modem did not answer
9
CONNECT 600
Connected, DTE to modem rate- 600bps
10
CONNECT 2400
Connected, DTE to modem rate- 2400bps
11
CONNECT 4800
Connected, DTE to modem rate-4800bps
12
CONNECT 9600
Connected, DTE to modem rate-9600bps
13
CONNECT 7200
Connected, DTE to modem rate-7200bps
14
LINE-IN-USE
When attempting to go off hook on a busy line
22
CONNECT 75/1200
V.23 or Bell 202 – forward/reverse channel
Extended Result Codes
23
CONNECT 1200/75
V.23 or Bell 202 – forward /reverse channel
40
CARRIER 300
Modem (DCE) connect speed-300bps
41
CARRIER 600
Modem (DCE) connect speed-600bps
44
CARRIER 1200/75
Modem (DCE) connect speed-1200/75bps
45
CARRIER 75/1200
Modem (DCE) connect speed -75/1200bps
46
CARRIER 1200
Modem (DCE) connect speed-1200bps
47
CARRIER 2400
Modem (DCE) connect speed-2400bps
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
Escape Sequence. The escape sequence consists
Register Reference Guide. Do not attempt to modify
of a “guard time” of one second (a period where no
S-Registers that are not listed in the table.
characters are sent to the modem), followed by 3
escape characters (typically +++ ), followed by
Table 4.
CH1788 S-Register Summary.
another guard time of one second.
The escape
Register
Function
character code is set in register S2. By default, the
S0*
Ring to Answer On
escape character is set as “+.” There is no required
S1
Ring Count
delay between characters.
When the escape
S2
Escape Code Character
sequence has successfully been sent, the escape
S3
Carriage Return Character
characters will not be transmitted to the remote
S4
Line Feed Character
modem.
S5
Back Space Character
S6
Wait for Dial tone
The CH1788 will stay Off-Hook with its carrier on after
S7
Wait for Data Carrier
the escape sequence is received. It will return an OK
S8
Pause Time for Comma
status message on RXD when it is ready to accept
commands. The CH1788 may be put into data mode
S9
Carrier Detect Response Time
again by issuing the command ATO .
S10
Lost Carrier to Hang-up Delay
S11
DTMF Tone On/Off
S13
DTMF Data/ Transmit Attenuation
AT COMMAND APPLICATIONS
S17
Ring Minimum Frequency
Dialing a phone number. The Dial command takes
S18
Ring Maximum Frequency
the form Dn , where n is a string of characters. In the
S23
Call Progress Functions
simplest form, n will be the digits of the phone
S30
Data Modulation Selection
number to be dialed.
S31
Data Modulation Status
S51
Ring/ Cadence A minimum On-Time
Example: Dial number.
S52
Ring/ Cadence A maximum On-Time
Enter:
ATD1234567<CR>
S53
Ring/ Cadence A minimum Off-Time
Result:
OK
S54
Ring/ Cadence A maximum Off-Time
S55
Ring/ Cadence B minimum On-Time
In the above example, the CH1788 dials the
S56
Ring/ Cadence B maximum On-Time
telephone number 1234567 , conducts handshaking
S57
Ring/ Cadence B minimum Off-Time
negotiations then waits for a carrier from the distant
S58
Ring/ Cadence B maximum Off-Time
modem. If a carrier is not detected within the time
S65
DTMF Detection
period specified by register S7, the CH1788 will
S66
Wait For Dial Tone Timer
automatically release the PSTN line and send the
S67
Minimum Duration Of Dial Tone
appropriate result code to the host. If a carrier is
S68
Test Timer
detected, the CH1788 will send the CONNECT result
S69
Test Error Count
code and will permit communication with the distant
S86
Hook Flash On Time
modem.
Note, the CH1788 is ready to send and
S89
Fast Connect/Pickup
receive data after the CONNECT result code is sent
S95
Caller ID configuration
or when an active signal is present on DCD. DCD
S110
Line-In-Use/ Parallel Pick-Up
line must be enabled with the ATC1 command.
Register
A variety of dial modifiers can be placed in the dialing
S111
Line-In-Use Setting Time
string to make it application specific. These include
pause, hook flash, pulse dialing, wait for dial tone,
Automatic Answering. Register S0 specifies the
etc. See the detailed D command.
number of rings that the CH1788 must detect before it
will answer. S0 may range in value from 0 to 255.
The Dial Command may also be issued without a
telephone number. ATD causes the modem to pick
S0 =0 DO NOT ANSWER TELEPHONE
up the telephone line without dialing a number.
S0 =1 ANSWER ON RING 1
S0 =2 ANSWER ON RING 2
Programmable S-Registers. The CH1788 contains
S0 =3 ANSWER ON RING 3
a variety of registers that store the configuration and
S0 =255 ANSWER ON RING 255
personality parameters for the CH1788. Both default
configuration
and
user
specified
configuration
When S0 is set to 0, the modem will not answer.
parameters are stored.
A summary of the S-
Registers is given in Table 4. A detailed description
of each is available in CH1788 Command and S-
2006 Cermetek Microelectronics, Inc.
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Cermetek Microelectronics, Inc.
CH1788 Surface Mount PLCC 2400bps Modem
IMPORTANT NOTE
greater to one another and 0.2 inch spacing or
The tables included in this data sheet are a
greater to all other traces.
The traces should
summary of the AT commands and S-Registers. A
have a nominal width of 0.020 inches or greater.
detailed description of all commands and registers is
available from Cermetek Microelectronics, Inc., and
5. The RING and TIP PCB traces should be as
should be consulted prior to design.
Refer to
short as possible and oriented to prevent
Cermetek publication CH1788 AT Commands and
coupling other high speed or high frequency
S-Registers Reference Guide or access our website
signals present on the host circuit PCB.
at http://www.cermetek.com .
6. No additional circuitry other than that shown may
Table 5. CH1788 AT Command Set Summary.
be connected between the modem module and
Basic
the RJ-11C jack.
Doing so will invalidate the
Commands
Function
FCC approval.
AT
Attention Code
7. The CH1788 requires external surge protection.
A
Answer command
This is mandatory to maintain FCC Part 68
A/
Repeat last Command
conveyed
approval.
Please
use
only
C
Carrier Detect DCD Signal Monitor
recommended components and values. Do not
D
Dial Command
use an MOV or a Transorb.
E
Off-Line Character Echo Option
F
Load Factory Default
8. The CH1788, the RJ-11C jack, the protection
H
Switch Hook Control Option
circuitry and all PCB traces in between, must be
I
Identification Option
contained on a PCB with a 94 V-0 flammability
K
DCE-DTE Flow Control
rating.
L
Fast Connect Option
N
Data
Set
Ready
DSR
Signal
9. The supplied FCC registration label must be
Monitor
applied visibly on the outside of the product.
O
On-Line Command
P
Pulse Dial
10. The product’s User Manual must provide the user
Q
Result Code Display Option
with instructions for connection and use as
R
Data Terminal Ready DTR Monitor
recommended in the FCC Registration Section
S
S Register Monitor
below.
T
Tone Dialing
V
Verbose / Numeric Result Codes
W
Extended Result Codes
CH1788
HANDLING
AND
ASSEMBLY
X
Result Code Set/Call Progress
RECOMMENDATIONS
Y
Async. Speed Buffered Option.
The CH1788 contains static-sensitive components
Z
Reset
and should only be handled by personnel and in
@T
Test Modes
areas that are properly protected against static
@Z
Power Down
discharge.
+++
Escape Sequence
Direct Soldering.
The CH1788 requires hand
soldered. All CH1788 products are moisture resistant
and will not be harmed by industry standard aqueous
PSTN LINE CONNECTION GUIDELINES
cleaning
processes.
Cermetek
does
NOT
1. The CH1788 must be mounted in the final
recommend SMD or wave soldering.
Cermetek
assembly such that it is isolated from exposure to
recommends against socketing the modem for
any hazardous voltages within the assembly.
production products.
However, for development
Adequate separation and restraint of cables and
purposes, a 68 pin PLCC socket may be used.
cords must be provided.
2. The circuitry from the CH1788 to the telephone
line interface must be provided in wiring that
FCC REGISTRATION
carries no other circuitry other than that
The CH1788 is registered with the FCC (Federal
specifically allowed in the FCC rules.
Communications Commission) under Part 68.
To
maintain the validity of the registration, the end
3. Connection to phone line should be made
product supplier must notify to the end user of the
through an approved RJ-11C jack.
product of several restrictions the FCC places on the
CH1788 and its use.
4. PCB traces from the modem’s RING and TIP pins
to the RJ-11C jack must be 0.1 inch spacing or
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
In addition to restriction notification, the FCC requires
If Problems Arise . If any telephone equipment is not
that Cermetek make all repairs to the CH1788. If
operating properly, it should immediately be removed
repairs are necessary after installation of the CH1788
from the PSTN line, as it may cause harm to the
in the end product and the end product has been
PSTN network. If the telephone company notes a
delivered to the end user, the end product must be
problem, they may temporarily discontinue service.
returned to the end product supplier where the
When practical, they will provide notification in
CH1788 can be removed and then forwarded to
advance of this disconnection. If advance notice is
Cermetek for repair.
The following notice is
not feasible, notification will be made as soon as
recommended and should be included in the end
possible.
product’s user manual.
If notified, the telephone company will allow the
opportunity
to
correct
the
problem
and
will
FOR YOUR USER’S MANUAL
acknowledge your right to file a complaint with the
The FCC Part 68 rules require the following (or
FCC. Contact the local telephone service provider
equivalent) be provided to the end user of equipment
with any questions about the local PSTN line.
containing a registered element.
In the event repairs are ever needed on the (insert
Type of Service . The (insert end product name) is
your product name), they should be performed by
designed to be used on standard device telephone
(insert your company name) or an authorized
lines. It connects to the telephone line by means of a
representative of (insert your company name). For
standard jack called the USOC RJ-11C (or USOC
information contact: (insert your company address).
RJ45S). Connection to telephone company provided
coin service (central office implemented systems) is
prohibited.
Connection to party lines service is
DEFAULT STATUS, PERFORMANCE, AND
subject to state tariffs.
SPECIFICATIONS
Changes in Attestation Procedure for Plugs and
Table 6. Summary of the Default Configuration
Jacks. (Name of applicant) attests that the network
Profile of the CH1788.
interface plugs or jacks used on this equipment
comply with and will continue to comply with the
Async speed buffer mode
mechanical requirements specified in Part 68, sub-
2400bps
part F, specifically the dimensions, tolerances and
V22bis, V.22, V.21 operation
metallic plating requirements.
The compliance of
Eight bits, No parity
these connectors will be assured by purchase
Auto answer disabled
specifications
and
incoming
inspection.
Fast connect disabled
Documentation
of
such
specifications
and/or
Flow control disabled
inspections will be provided to the FCC within 30
Command echo ON
days of their request for same.
All result codes enabled – non extended
Verbose result codes
Telephone Company Procedures. The goal of the
DSR, DTR, DCD ignored by the modem
telephone company is to provide the best service it
Guard tones disabled
can.
In order to do this, it may occasionally be
Minimum DTR pulse width =0.1 seconds
necessary for them to make changes in their
Ring count =00
equipment, operations or procedures.
If these
Escape code character =43 (+)
changes might affect the service or the operation of
Carriage return character =13
equipment, the telephone company will provide
Line feed character =10
notice, in writing, to allow time to make any changes
Back space character =08
necessary to maintain uninterrupted service.
Duration of wait for dial tone =02 seconds
Duration of wait for carrier after dialing =50 seconds
In certain circumstances, it may be necessary for the
Duration of dial pulse (comma)=02 seconds
telephone company to request information from you
Carrier detect response time =600ms
concerning the equipment which you have connected
Escape code guard time =1 second
to your telephone line.
Upon request of the
Last carrier to hang up delay =1.4 seconds
telephone company, provide the FCC registration
Flash on/off 500ms.
number and the ringer equivalence number (REN);
Ring frequency 10-75 Hz.
both of these items are listed on the equipment label.
Power down idle mode inactivity on
The sum of all of the REN’s on your telephone lines
Long space disconnect disabled
should be less than five in order to assure proper
service from the telephone company.
2006 Cermetek Microelectronics, Inc.
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Document No. 607-0018 Revision A6 (01/06)
Cermetek Microelectronics, Inc.
CH1788 Surface Mount PLCC 2400bps Modem
Figure 3.
PSTN Line Interface for all CH1788 Products.
1. Current Limiting PSTN Protection Line
The Sidactor or equivalent should be nominally
Device.
rated at between 270-300 Volts.
In most
Current limiting devices are mandatory to meet UL
environments, 2 terminal surge suppressors are
safety standards. To maintain conveyed FCC Part
adequate.
For severe environments, use an
68 approval, the current limiting components
external 3 terminal device with an earth ground as
identified as F1 and F2 in dashed Box 1 must be
is shown.
included. Refer to Cermetek Application Note #
126, Supplemental PSTN Line Protection, for
more details. Refer to Cermetek Application Note
4. EMI/RFI Suppression.
# 130, Summary of Recommended Suppliers, for
EMI/RFI suppression is recommended. This is for
a list of suppliers and manufactures part numbers.
obtaining FCC part 15 A and/or B. It is also used
to suppress external EMI / RFI signals that can
affect modem operation, such as strong radio
A resettable/repairable fuse (rated at 0.15 amps)
signals, should the modem be near a source of
is preferred because it resets automatically upon
such signals.
No external EMI/RFI noise
removal of the current flow.
Non-resettable
suppression circuitry is required to maintain
devices are also acceptable. Although CSA CS-
conveyed FCC Part 68 approval.
Additional
03 Part 1 (Canada) follows the requirements of
suppression may be added as described below
FCC Part 68 (USA), Cermetek recommends
without adversely affecting FCC Part 68 approval.
contacting DOT (Canada) and/or a certified
independent lab to verify compliance.
A. To provide adequate EMI/RFI suppression,
2. PSTN Current Limiting Resistors.
the capacitor/inductor network contained in
dashed Box 4 should be located as close to
Low value (10 Ω ) 1/2 watt resistors may be
the RJ-11C Jack as possible.
Further, this
required (identified as R1 and R2 in dashed Box
network should be provided with an excellent
2),
depending
on
end
product
application
ground path to the chassis.
environment, to enhance performance by reducing
susceptibility to PSTN current surges that may
B. Capacitors C1 and C2 should not exceed
occur before the OVERVOLTAGE PROTECTION
0.005 µ f. They must have a rating of 1.5KV
device (identified as D1 in dashed Box 3)
and typically are 0.001 µ f ± 20%. Inductors L1
becomes fully activated.
and L2 may be either individual inductors or a
dual inductor. Refer to Application Note #130
Refer to Cermetek Application Note # 130,
for a complete list of recommended vendors
Summary of Recommended Supplies, for a list of
and associated part numbers.
For UL
suppliers.
applications, choose capacitors and inductors
that are UL 1950 listed. The actual values of
the components used may vary depending on
3. Over Voltage and Lightning Protection.
the end product design and the nature of the
To maintain conveyed FCC Part 68 approval for all
EMI/ RFI. Consult an FCC part 15 consultant
CH1788 Products, the required surge protection
if required.
must be supplied externally. It is required that a
Sidactor or equivalent fast acting device be used.
DO NOT USE AN MOV OR A TRANSORB.
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
Table 7. CH1788 System Data Mode Compatibility Specifications.
Parameter
Specification
Parameter
Specification
Asynchronous
2400,
1200
bps
character
Receive Carrier
Originate 2400Hz ± 7Hz
asynchronous.
Frequencies
Answer
1200Hz ± 7Hz
300 bps asynchronous
V.22 bis, V.22,
212A
Asynchronous
TXD may differ +/-2.5% from
Bell 103
Answer
‘space’ 2020Hz ± 7Hz
Speed Range
modem output.
Offsets will be
Answer
‘mark’
2225Hz ± 7Hz
corrected by adding/ deleting stop
Originate ’space’ 1070Hz ± 7Hz
bits.
Originate ‘mark’
1270Hz ± 7Hz
Asynchronous
10 bits, including start, stop,
Receiver
Carrier detect ON threshold
Format
parity.
Sensitivity
-43dBm
Carrier detect OFF threshold
-48dBm
Telephone
Line
Two-wire full duplex over public
Billing Delay
2.0 to 3.0 seconds
Interface
switched network. On-chip hybrid
and billing delay timers.
Transmit level
V.22 bis, 16 point QAM at 600
Power
-9.6dB max-QAM
baud.
V.22 and 212A, 4 point
-7.4dB max.-DPSK
DPSK at 600 baud. 103 Binary
-5.3dB max-FSK
phase coherent FSK.
Self Test Pattern
Alternate ‘ones’ and ‘zeros’ and
Line
Fixed compromise equalization,
Generator
error detector, to be used along
Equalization
transmit.
Adaptive equalizer for
with most loopbacks. A number
DPSK/QAM, receive.
indicating the bit errors detected
is sent to DTE.
Transmit Carrier
Originate 1200Hz ± .01%
Diagnostic
Local analog loopback.
Frequencies V.22
Answer
2400Hz ± .01%
Available
Local analog loopback.
bis, V.22, 212A
Remote digital loopback.
Request remote digital loopback.
Local interface loopback modem
with self-test.
Bell 103
Originate ’space’ 1070Hz ± .01%
Call Progress
With speaker or quiet screen
Originate ‘mark’
1270Hz ± .01%
Tones Detected
messages (No dial tone, busy,
Answer
‘space’ 2020Hz ± .01%
ring-back, modem answer tone
Answer
‘mark’
2225Hz ± .01%
and voice).
Computer
Interface
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
Table 8. CH1788 D.C. Electrical Specifications.
Parameter
Description
Min.
Typ.
Max.
Units
V CC
Positive Supply Voltage- Noise less than 50mV
5V
4.75
5.0
5.3
V
3.3V
2.70
3.30
3.60
Idd1
Nominal Operating Current
5V
51
62
mA
3.3V
16
Idd2
Power Down Idle mode Current
5V
3.0
mA
3.3V
2.5
Idd3
Power Down “Zero” Mode Current
5V
15
uA
3.3V
10
V IH
High Level Input Voltage*
5V
V CC /2
V
3.3V
0.2 V CC
+5.5
V IL
Low Level Input Voltage*
5V
.50
V
3.3V
0.2 V CC
I IN
Input Leakage Current – All Pins
1
uA
V OH
High Level @ -4mA 5V and 3.3V
V CC -.45
V
V OL
Low Level @ 4mA
5V
0.6
V
3.3V
0.45
Test conditions:
CH1788 VCC = 5V ± 10%, Temp = 0 ° C to 70 ° F.
CH1788-3 VCC = 3.3V ± 10%, Temp = 0 ° C to 70 ° F
*Output Load = 30 pF ± one TTL.
Table 9. CH1788 Operational Specifications.
Parameter
Minimum
Typical
Maximum
Units
Comments
Off Hook Impedance
600
Ohms
Trans Hybrid Loss
25
dB
600 Ohm, RXA, TXA
Ring Voltage Loop
110V
250V
V pp
On 48VDC line voltage offset
for sustained periods of
seconds.
Line Loop Current-(Off-
20
80
mA
Hook)
Return Loss @ 1000Hz
15
dB
600 Ohm
Ring Frequencies
10
20
75
Hz
Receiver Insertion Gain
-0.5
0.0
+0.5
dBm
600 Ohm- Data Mode
Transmit Power
-10.0
dBm
When recommended
initialization is used.
First Character After Reset
0.5
2.0
sec
Delay
Inter Character Delay
0
50
msec
Between all command
characters
Command Delay
125
150
msec
Between all AT commands
Minimum Reset Pulse
50
msec
If user supplied
Duration
2006 Cermetek Microelectronics, Inc.
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CH1788 Surface Mount PLCC 2400bps Modem
Table 10. Other Performance Specifications.
Parameter
Minimum
Typical
Maximum
Units
Comments
Tone 2 Harmonic
nd
-35
dB
HYB enabled into 600 Ω
Distortion
DTMF Twist (Balance)
2
dB
DTMF Tone Duration
50
255
ms
95ms default
Pulse Dialing Rate
8
10
20
pps
10pps default
Pulse Dialing Make/
39/61
%
US, Canada default
Break
Pulse Interdigit Interval
700
3000
ms
789ms default
Guard Tone Frequency
550
Hz
Referenced to High Channel
Transmit
Guard Tone Amplitude
-6
dB
Referenced to High Channel
Transmit
Guard Tone Frequency
1800
Hz
Referenced to High Channel
Transmit
Guard Tone Amplitude
-9
dB
Referenced to High Channel
Transmit
High Channel Transmit
-1
dB
Referenced to Low channel,
Amplitude
Guard tone enabled
nd
Guard Tone 2
-40
dB
Harmonic Distortion
Call Progress
120
620
Hz
Passband Frequency
Wait Time for Dial tone
2
255
sec
Two second default
Return loss @ 1000Hz
30
dB
T r =600 Ω + 2.16 µF
Table 11. Summary CH1788 Family of Products.
Model
Summary of Features
Operating
Temperature
CH1788
5V, Full function, FCC Part 68 approved, UL 1950 Listed, Hermetic
0°C to 70°C
CH1788ET
5V, Full function, FCC Part 68 approved, UL 1950 Listed, Hermetic
-40°C to 85°C
CH1788-3
3.3V, Full function, FCC Part 68 approved, UL 1950 Listed, Hermetic
0°C to 70°C
CH1788-3ET
3.3V, Full function, FCC Part 68 approved, UL 1950 Listed, Hermetic
-40°C to 85°C
2006 Cermetek Microelectronics, Inc.
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Document No. 607-0018 Revision A6 (01/06)
Cermetek Microelectronics, Inc.
CH1788 Surface Mount PLCC 2400bps Modem
Package
Outline
Note
1. All dimensions indicated are nominal and listed in inches.
2. SMD solder landing pads: 0.120 inches x 0.025 inches.
Figure 4.
Recommended CH1788 PCB Layout Footprint.
2006 Cermetek Microelectronics, Inc.
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Document No. 607-0018 Revision A6 (01/06)
Cermetek Microelectronics, Inc.
CH1788 Surface Mount PLCC 2400bps Modem
SIDE VIEW
Dimension
MIN
TYP
MAX
a
0.250
0.255
0.260
b
0.985
0.990
0.995
c
0.945
0.950
0.955
d
0.825
0.830
0.835
e
0.045
0.050
0.055
f
0.495
0.500
0.505
g
0.010
0.020
0.030
h
0.170
0.175
0.180
i
0.000
0.010
0.020
TOP VIEW
j
0.270
0.275
0.280
k
0.025
0.030
0.035
l
0.015
0.020
0.025
m
0.035
0.040
0.045
NOTE
Pins can be custom formed to
meet
unique
requirements.
Contact Cermetek for special
order requirements.
Figure 5.
CH1788 Physical Dimensions.
Table 12.
CH1788 Pin Functions.
PACKAGE CONNECTION TABLE
PIN NO.
FUNCTION
PIN NO.
FUNCTION
1
A1
12
RING
2
OH *
13
TIP
3
RTS*
14
V+
4
RI*
15
V-
5
CTS *
16
OPEN
6
DSR*
17
OPEN
7
DCD*
18
S1
8
DTR*
19
S2
9
A2*
20
V CC
10
TXD
21
GND
11
RST
22
RXD
* Active Low
2006 Cermetek Microelectronics, Inc.
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Document No. 607-0018 Revision A6 (01/06)
Cermetek Microelectronics, Inc.
CH1788 Surface Mount PLCC 2400bps Modem
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 Approvable 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
1390 BORREGAS AVENUE | SUNNYVALE CA 94089 | LOCAL: 408-752-5000 | TOLL FREE: 1-800-882-6271 | FAX: 408-752-5004
CERMETEK WEB SITE: http://www.cermetek.com | EMAIL: sales@cermetek.com
2006 Cermetek Microelectronics, Inc.
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Document No. 607-0018 Revision A6 (01/06)