operates exclusively on non-voltage bearing leased line. The HS Modem family is pin compatible with Cermetek's low cost V.22bis, 2400bps modem family. Each module in the HS Modem family is a self-contained modem and is FCC Part 68 approved and Canadian DOT approvable. Additionally, the CH1794TBR/ETBR, the CH1799TBR/ETBR and the CH2056TBR/ETBR products meet the European TBR21 requirements. These ultra small modules are designed for PCB through-hole mounting and are x 0.61" (nominal, 0.55" upon request) in size. The HS Modem family requires only two external interfaces: a CCITT V.24 serial interface for direct access to a UART, and a Tip and Ring RJ-11C Jack for the PSTN line connection. The HS Modem can be controlled with industry standard AT commands and is compatible with available industry communication software.
Supports V.23, V.21, Bell 212A and 103. CH2056 supports V.80 Synchronous operation. Error correcting: V.42 LAMP, MNP 2-4 and MNP10. Data Compression: V.42bis and MNP 5 MNP10 Data through put enhancement for cellular operation. DTE serial interface with speeds 57.6kbps (CH1794). Automatic baud rate adaptability utilizing speed sensing, flow control and data buffers. Send & Receive FAX class 1, Group 3 supported. Serial V.24, 5 volt interface. NVRAM directory and stored profiles. AT Command structure, with extensions. Built-in DAA with 1500 VAC RMS isolation 2122V peak surge protection. UL 1950 and CSA C22.2 950 Recognized (E104957). Leased Line version available CH1799LL FCC part 68 Approved/DOT CSA CS-03 Part I Approvable. +5 Volt operation with zero power option Small size: x 0.61" (nominal, 0.55" upon request). Pin compatible with low speed/low cost CH1786 TBR21 compliant versions available: CH1794TBR/ETBR, CH1799TBR/ETBR and CH2056TBR/ETBR.DESCRIPTION OF FUNCTIONAL BLOCKS AND DISCUSSION OF BASIC OPERATIONS
Figure 1 contains a functional block drawing of the HS Modem family of products. Each HS Modem product consists of a serial interface buffer, modulator/demodulator, modem controller with error correction and data compression, non-volatile RAM and a DAA.
The CH2056, CH1799 and CH1794 (HS Modem Family) are industrial grade high-speed modem modules. Each HS Modem product supports a range of modem standards and speeds from 57,600bps. By using built in compression algorithms the operation speed can be expanded to the maximum DTE rate of 57.6kbps for the CH1794, 115.2kbps for the CH1799 and 230.4kbps for the CH2056. A choice of error correcting schemes is available including MNP 10 for cellular telephone applications. The HS Modem family supports Send and Receive FAX. The CH1799LLFigure 1. Functional Block Diagram of HS Modem Family.
Serial Host Interface Buffer. The HS Modem utilizes a serial V.24 EIA 232-E 5V interface to control the modem. The HS Modem products can communicate over the serial interface with the Data Terminal Equipment (DTE) at a fixed speed regardless of the carrier line modulation speed (DCE) of the PSTN modem connection. This eliminates the need to have the DTE step up or step down in speed based on the in-coming or out-going PSTN communication data rate. Hence, the DTE can train the CH2056, to say 56kbps, and talk to a slower in-coming data connection at say, 2400bps without changing host speed. Conversely, the host DTE trained at 14.4kbps can also communicate with the modems at higher speeds, say 28.8kbps. This is accomplished by invoking internal automatic data flow control. The HS Modem family has a resident buffer to allow for this auto baud operation. Non-Volatile RAM (NVRAM). NVRAM can store user-customized configurations. The AT&Wn command will store the active modem configuration in one of two NVRAM locations as selected or 1. The AT&Yn command selects one of the stored modem configurations to be automatically recalled and made active upon reset or power up. The ATZn command immediately recalls and activates a stored configuration. See Tables 7A and 7B for storable SRegisters and Commands. The NVRAM can save up to four telephone numbers, with to 31 digits or modifiers in each telephone number. The AT&Zn=s command will store s, the telephone number dial string. The ATDS=n command will cause the modem to dial one of the four stored telephone numbers. The NVRAM storage location for the four telephone numbers is selected or 3. Telephone Line Interface or DAA. High performance modems are extremely sensitive to DAA (Data Access Arrangement) performance. The difference between a good modem and a fair one is in the DAA performance. The HS Modem family includes a unique low distortion DAA designed for optimal performance over all PSTN line conditions thereby achieving the most reliable and best performance PSTN connections. The HS Modem family is designed to meet North American telephone standards as set by the FCC Part 68 (USA) and CSA CS-03 Part I (Canada). Among the more critical parameters, the PSTN line interface is designed to meet 1500 VAC RMS isolation and provide 2122V peak surge protection. Consequently, the HS Modem family of products satisfies U.S. and Canadian requirements, and will meet other international approval agency requirements that specify these levels of isolation. The TBR/ETBR variants also meet the European TBR21 requirements.
Pins 1 and 2 function as both input and output connections to the PSTN. To maximize field reliability in hostile environments, for Canadian approval, for UL compliance, and also optionally for FCC Part 15 compliance, these two pins must be routed through an external network such as that briefly described in Figure 6A and described in more detail in Cermetek Application Note # 126. Each HS Modem product comes with FCC Part 68 approval and is shipped from the factory with an FCC Label indicating registration number and ringer equivalent. This label should be prominently displayed on the end product. With the exception of the U.S., most countries (including Canada) require submission of the final product or system containing the HS Modem to the appropriate governing regulatory agency for approval. Typically this is accomplished by submitting the final end product to an independent test house or consultant for evaluation. The test house/consultant then forwards the test results and applicable documents to the regulatory agency. Contact Cermetek for a list of suggested consultants. Modulation/Demodulation/Error Correcting and Data Compression. These functions are provided by an industry standard modem chip set which has been adapted for use with the HS Modem family. The Modulation/Demodulation scheme supports the industry modem standards listed below. SUPPORTED MODULATION STANDARDS Bell 103 CCITT V.22 Bell212A CCITT V.22bis CCITT V.32 CCITT V.32bis CCITT V.34 CCITT V.34bis CCITT V.90 The HS Modem supports V.42 LAMP, MNP 2-4, MNP 10 error correcting protocols. The CH1794 uses MNP5 data compression techniques and the CH1799/CH2056 uses V.42bis data compression, allowing data transmission rates to a maximum of 57.6kbps/115.2kbps/230.4kbps, respectively. These high DTE data rates are supported by the HS Modem serial interface via its auto baud capability. Note that the maximum speed attained is limited by the maximum speed available from the DTE. The resident Modulator/Demodulator supports line equalization and forward error correction. IMPORTANT NOTE The V.90 standard prescribes 56kbps downlink and 33.6kbps uplink. Consequently, two V.90 modems connected back-to-back will send at 33.6kbps.
Since a modem communicates data serially and most host products handle data in a parallel format, a UART is needed to make parallel-to-serial and serial-toparallel translations.
Modem is powered down. The internal blocking diode provides supply isolation. The pins of the HS Modem will in an undefined state when powered is switched off. This must be taken into consideration to assure that no unwanted signals are presented to the HS Modem during power down.
AT Command Set. The HS Modem supports the AT Command set with extensions and can operate with industry standard communication software. The AT Commands are compatible with TR302.2/88-08006. Serial Host Interface. The HS Modem family operates in asynchronous mode and supports 5V, RS232- like interface called V.24 (EIA-232-E). The HS Modem supports a full RS-232C/V.24 serial interface. Signal levels are TTL rather than RS-232C level compatible, which allows direct connection of the HS Modem to the host's UART without level translating circuitry. See Table 3 for a complete set of pin descriptions. The modem is controlled by sending serial commands over TXD and by monitoring serial status messages returned on RXD. All other serial interface lines may be utilized for the convenience of a particular application but are not required by the modem. Unused outputs from the HS Modem should be left unconnected. Unused inputs should be tied to the proper logic level. See Table 3. Speaker Interface. The SPK output reflects the receiver analog input and provides a signal that can be used to monitor call progress. The SPK signal can drive a 300-ohm load directly. Typically, the SPK signal is input into an audio power amplifier and the amplifier, in turn, drives the speaker coil. The speaker is activated with the ATM command. The speaker volume is adjusted using the ATLn command; where or 3. Increasing numbers correspond to higher volume. Figure 3 indicates one method of driving an external 8-ohm speaker. Zero Power Mode. If an application calls for zero power during standby periods, the power may be switched off using external circuitry and then reapplied when the HS Modem's RI pin becomes active. The HS Modem can thus be powered down to zero. Referring to Figure 2, the controller activates the relay switch, supplying power (+5V) to the HS Modem. In this configuration, the ring signal is used to "wake up" the HS Modem when the HS Modem is in the power down state. The internal structure of the RI pin consists of an open collector opto transistor with a 30k ohm pull-up through a blocking diode to 5V. The user should apply his own pull-up resistor to an active 5V source when the HS
Figure 2. Zero Power Operation. Power Supply. The HS Modem module is a complex set of sensitive subsystems. During the course of normal operation, the HS Modem decodes analog signals from the telephone line that are in the millivolt range. Steps must be taken by the user to guarantee that power supply noise on all supply lines, including ground, does not exceed 25mV peak to peak. If necessary, use dedicated power and ground planes. Failure to provide such operating conditions could cause the HS Modem to malfunction or to function erratically. The HS Modem family requires +5V �5% supply. It is recommended that bypass capacitors be placed on the power supply as close to the HS Modem's supply input pins as practical. It is recommended that �F or greater tantalum capacitor in parallel with 0.1 �F ceramic capacitor be used. The user must also provide shielding from nearby sources of EMI, such as relays, motors and other power supplies. Automatic Speed/Format Sensing. The HS Modem supports both Command and Data modes of operation. The HS Modem can automatically determine the speed and format of the data sent from the DTE over the serial interface; and can sense the following broad range of speeds: