CH1786NE Datasheet

Low Speed Modem


Features, Applications

The CH1786 family of modems are a full function, FCC Part 68 approved 2400bps modem. These modems provide a fast, easy and flexible way to integrate a modem into any OEM product while utilizing the minimum amount of PCB space "x 0.52 The CH1786 family only requires two external interfaces: a CCITT V.24 serial interface that can be routed directly to a UART, and a Tip and Ring interface which goes directly an RJ-11 jack for the PSTN line connection. The CH1786 can be controlled with industry standard AT commands and, hence, is compatible with available industry communication software. All CH1786 modems support asynchronous operation 2400bps, 1200bps, and 300bps to both Bell and CCITT standards. The resident PSTN line interface, or Data Access Arrangement (DAA), while being FCC approved, is also Canadian DOT approvable and can be approved in other countries that require 1500VAC RMS isolation requirements per UL 1950 Edition 3. The CH1786 family of modems operate off a single 5volt supply. The low power operation and automatic standby mode make these modems ideally suited for portable equipment. In addition, their small physical size affords maximum flexibility in equipment design.


FCC Part 68 approved and DOT CSA CS-03 Part I approvable UL 1950 and CSA C22.2 950 Listed UL File Number: E104957 AT Command structure with extensions 1500 VAC RMS isolation barrier minimum, 2122V peak surge protection minimum Single 5 volt operation Low power operation with automatic reduced power standby mode Automatic adaptive equalization and fixed compromise

Size: "x 0.52 "(nominal) NVRAM allows storage of custom configurations and telephone numbers
CH1786 NVRAM, Voice/ Inject, Operating Temperature: to +70�C Hermetic,

NVRAM, Voice/ Inject, Hermetic, Operating Temperature: to +85�C Non-Hermetic, Operating Temperature: to +70�C

Figure 1. Functional Block Diagram of CH1786. The CH1786 comes with FCC Part 68 approval and is shipped from the factory with an FCC Part 68 label indicating the registration number and ringer equivalent. This label should be prominently displayed on the end product.


Figure 1 contains a functional block drawing of the CH1786. The is a highly integrated, fullfunction modem, comprised of a modulator/ demodulator, controller, NVRAM and an FCC Part 68 approved and C22.2 950 listed PSTN line interface. Modulation/Demodulation and Modem Controller. These functions are provided by a monolithic modem integrated circuit. This IC has built-in facilities to accommodate integrated AT command control and contains the necessary resident interfaces for general communication and routing to the DAA. Telephone Line Interface or DAA. The CH1786 family of modems is designed to meet 1500VAC RMS isolation and provide 2122V peak surge protection. Consequently, the CH1786 satisfies U.S. FCC Part 68 and DOT CSA CS-03 Part I Canadian requirements, and will meet other international approval agency requirements that specify these levels of isolation. With the exception of the U.S., most countries (including Canada) require submission of the final product or system containing the CH1786 to the appropriate governing regulatory agency for approval. Typically this is accomplished by submitting the final end product to an independent test house or consultant for evaluation. The test house or consultant then forwards the test results and applicable documents to the regulatory agency. Call Cermetek for a list of suggested consultants. Non-Volatile RAM (NVRAM). The NVRAM present on the CH1786 is sufficient to store up to two user customized modem configurations. The AT&Wn command will store the active modem configuration in the selected NVRAM locations by specifying or 1. The AT&Yn command selects the modem configurations to be automatically recalled and made active upon a reset or power up. The ATZn command immediately recalls and activates a stored configuration. Refer to Tables 4, 5 and 6 for storable S-Registers and available commands. The NVRAM can save up to four telephone numbers with to 36 digits or modifiers in each telephone number. The AT&Zn=s command will store s, the telephone number dial string. The individual NVRAM telephone number storage locations are selected by specifying 0,1,2,or 3. The ATDTS=n command will cause the modem to dial the stored telephone number in location n. NVRAM is not available on the or CH1786NH.

AT Command Set. A 40-character command line is supported. The command line starts with AT and may contain standard or enhanced commands. The commands are compatible with EIA Document TR302.2/88-08006. Serial Host Interface. The serial interface V.24 (EIA-232) compatible interface. Ten Bits total: 1 start bit, 1 stop bit, and eight data bits which can be either eight bits with no parity or seven odd or even with parity. The start bit is LOW going. RXD and TXD data is non-inverted. See pin description in Table 2. Speaker Interface. The SPK output reflects the receiver analog input and provides a signal that can be used to monitor call progress. The SPK signal can drive a 300 load directly. Typically, the SPK signal is input into an audio power amplifier and the amplifier, in turn, drives the speaker coil. The speaker is activated with the ATMn command. The speaker volume is adjusted using the ATLn command, where 0,1,2,or 3. Increasing numbers correspond to higher volume. Figure 6 indicates one method of driving an external 8 speaker. Phone Control. Cermetek 's CH1786 contains a pin called Voice or Data (V/D). The V/D pin toggles high when the modem goes off hook. This pin can be used to activate a relay which can switch a telephone on or off the Tip and Ring incoming PSTN lines. This feature allows any telephone associated with the to be disconnected when a data call is in progress, thereby preventing the data from being disturbed by an inadvertent telephone pick-up. See Figure 2. Speed and Parity Selection. Prior to call initiation, the host controller trains the modem to the host speed or 300bps) and parity (odd, even, mark, space, or none) via a host-initiated training sequence. This training also sets the speed of the data for originate calls. The CH1786 will automatically adjust to the originator's speed when answering calls. The CH1786 matches the host's parity when it returns status messages to the host. During a data connection, however, the modem passes parity through without interpretation or alteration. Sleep Mode. To minimize power consumption, the CH1786 includes a power down feature called Sleep Mode. When activated, the CH1786 will automatically enter Sleep Mode after to 254 seconds of inactivity. The inactivity delay is selected using the ATS24 command. The CH1786 is delivered from the factory with a 5 second inactivity delay enabled (i.e., ATS24=5). The CH1786 returns to normal operation when a ring signal is received or

upon an input low signal on the TXD pin. ATS24=255 disables the Sleep Mode and is the default if no value is set in register S24. A SLEEP output signal is available to control power to external devices. In Figure 6, a FET controlled by the SLEEP signal turns of the external speaker amplifier when the CH1786 enters Sleep Mode. In Sleep Mode, power is reduced to approximately 50% of normal operating power. Guard Tone. A guard tone 1800 Hz can be generated 9 dB below the transmit level, respectively, by using the &Gn command. Refer to "Cermetek AT Commands and S-Registers reference Guide" or the Cermetek web site at http://www.cermetek.com. Answer Tone. A CCITT (2100 Hz) or Bell (2225Hz) answer tone is generated depending on the selected configuration. Refer to "Cermetek AT commands and S-Registers Reference Guide" or the Cermetek web site at http://www.cermetek.com. Data Encoding. The data encoding conforms to CCITT recommendations or 103, depending on the selected configuration. Refer to "Cermetek AT commands and S-Register Reference Guide" or the Cermetek web site at http://www.cermetek.com. Line Equalization. Transmitter and receiver digital filters compensate for delay and amplitude distortion during operation on nominal phone lines. In addition, automatic adaptive equalization in the receiver minimizes the effects of inter symbol interference. Transmission Speed. In normal operation, the originating modem initiates the call and attempts to connect to the answering modem at a speed established by the originating modem's controller prior to call initiation. This is referred to as the Initial Trained Rate. Upon receiving the call, the answering modem will attempt to connect to the originating modem at its Initial Trained Rate. If these two rates are identical, the connection is made. If the speeds differ, the answering modem must adjust its rate or terminate the call. Table 1 indicates the connection rate that will result when the calling modem's Initial Trained Rate and the answering modem's Initial Trained Rate are different. NOTE A 2400-baud connection rate will only result if both modems are initially set at 2400 baud. Zero Power Mode (CH1786ET only). If an application calls for zero power during standby periods, the power may be switched off using external circuitry and then reapplied when the 's RI

pin becomes active. The CH1786ET products can thus be powered down to zero. Table 1. Connection Rates. Answering Connection Rate Resulting Modem Initial When Calling Modem Initial Trained Rate Is:

Figure 3. Zero Power Operation. Referring to Figure 3, the controller activates the relay switch, supplying power (+5V) to the CH1786ET. In this configuration, the ring signal is used to "wake up" the CH1786ET when the is in the power down state. The pins of the CH1786ET will in an undefined state when power is switched off. This must be taken into consideration to assure that no unwanted signals are presented to the CH1786ET during power down. Ring Indicator (RI). The RI pin follows the frequency of the ring signal and toggles low when the CH1786 detects an incoming call. The ring signal is typically 30 Hz and is on for 2 seconds and off for 4 seconds. Although not TTL compliant, the RI pin can, nonetheless, be utilized to activate external circuitry including the external RST pin. When using the RI pin, it is recommended that a Schmitt Trigger or the Isolated Envelope Detect Circuit in Figures 5 be placed between the RI pin and the external load. Power Supply. The CH1786 modem module is a complex set of sub-systems. During the course of



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