Using the TERIDIAN 73M2901CE In a TERIDIAN K-Series Application

Transcription

1 M0CE V.bis Single Chip Modem AN_0 APPLICATION NOTE JULY 00 Using the TEDIAN M0CE In a TEDIAN KSeries Application The KSeries of modem data pumps are, in a few cases, being discontinued due to the their processes becoming obsolete and unavailable. This applies to the older, lower volume KSeries products, specifically the K0L and KL. In order to better support some of the applications that these discontinued products are being use in, we have added enhancements to the 0 family of modems. The TEDIAN M0 family of integrated circuit modems provides all the microprocessor control, modulation, and demodulation functions required to implement an intelligent low speed modem. The M0 family can be thought of as a KSeries modem data pump combined with an 0C controller in a single integrated circuit. All the complex handshaking, detection, and modem configuration operations can be controlled through highlevel, Hayes AT style commands, greatly reducing the code development required to implement the modem s functions. The latest member of the 0 family is the M0CE. The CE includes some new functions such as enhanced leased line modes, energy ring detection, and SMS support, among other features. Now that the K0L and KL are reaching endoflife, there is need to design in replacements for them in products that are still being manufactured and have a long lifetime remaining. There are fundamental differences in the architectures of the KSeries and 0 family, but since the 0 can be thought of as a superset of the K Series, in most cases this means hardware can be eliminated and the design simplified when going to the 0. Figure below shows a typical standalone KSeries modem design. A dedicated controller is being used for the modem only. This dedicated controller can be eliminated since all the modem control functions are included in the M0 family of modems. In addition, the KSeries requires external op amps for the hybrid circuit; these are also included in the M0 family. If the K Series design uses a controller that is shared with other product functions, the digital interface will still usually be simpler when using the M0CE. Instead of needing to program every aspect of the modem functions through register reads and writes to a parallel bus, the modem can be controlled through high level AT commands to the serial data interface that is connected to the Host processor in the same way as the KSeries data pumps they are replacing. VCC_D 0 0 OH NVSK RST NGD TXINT NVRM NVCE WR RD X X GND VDD 0 AD0 AD AD AD AD AD AD AD XEN ALE 0 PSEN TR MR AA CD VC HS VC AUX VCC 0 CLK XTL XTL AD0 AD AD AD AD AD AD AD ALE WR RD KL GND RXA ISET 0 CS EXCLK INT TXA VDD VCC REF V 0 T A C A C RJ CFB Figure. Typical K Series Modem Design In applications where the KSeries is being used, the M0 family can also be used. A relatively simple hardware changeover is usually all that is needed since the analog interface of the M0 is identical to the K Series B version devices with internal hybrids. The digital data interface is also the same as the KSeries and

2 AN_0 Using the M0CE in a KSeries Application can easily be connected (see Figure ). Until recently the only applications where there may have been significant redesign required were where the KSeries was used in certain nonstandard applications or where the modem was not being used in a dialup connection. Specifically the earlier versions of the 0 were optimized for dialup applications, so leased line and wire modes were not a simple change over. The M0CE now addresses those other applications in addition to support for leased line modes. Leased line mode allows modems to connect without some of the restrictions and timeouts that are required for dialup operation. It also allows the modems to remain active when the modems are disconnected or carrier is lost for a period. When carrier is detected, the modems will reconnect and then resume normal operation. A new is used to enable the leased line mode for all modulation types. First, the modulation mode should be selected using S0. Only one mode should be selected in S0 since with leased lines the speed and modulation mode will always be known is used to enable leased line mode and then an ATD or ATA are used to initiate the connection. The modem immediately goes off hook, sends its carrier in the selected mode and waits for the other modem carrier to appear. The connection between the modems can be interrupted and reestablished without having to do another complete handshake. This is also convenient in many other applications where it is desirable to connect two or more modems as simply as possible. VCC_D VCC_D M0CE_MLF/TQFP 0 USR0 NG 0 OSCIN USR USR0 RXA VBG TXAP TXAN VPA 0 VCC_A VCC_D RJ VCC_D VCC_D Figure. M0CE based design with the same functions as figure Plus Caller ID USING THE M0CE IN KSEES APPLICATIONS The M0CE does have some limitations that should be noted. First, the M0CE is a.vpowered device and cannot be used with a V power supply. All the digital inputs and outputs are V logic tolerant, so it can still interface with existing V logic. All that is needed is a small inexpensive terminal regulator to supply power to the modem. While V. has several different modes and a low speed reverse channel, the Bell 0 mode is currently supported only in two modes, half duplex and wire full duplex. ATB selects the 0S HDX receive mode and ATB selects the Bell 0S transmit mode. Neither the low speed back channel nor carrier turnaround (ping pong mode are supported. In addition, M0CE Bell 0 modes do not include an internal control to turn the transmit signal on and off as in the V. SMS mode. In order to do carrier turnaround, the wire leased line mode can be used with the transmit signal or receive path switched to accomplish the turnaround. Low cost, low on resistance analog switches are now available from Philips in the LVC0. Figure shows a method that could be used in dialup wire applications. Since the carrier is usually controlled by the signal, it can be used to also switch the transmit and receive channels to accomplish turnaround. USING THE M0CE IN WIRE MODE The M0CE supports wire full duplex in the main channel for both Bell 0T (as in the K0L) and V. (as in the KL). Figure shows a typical application for a wire configuration. The ATBn commands are used to put the modem into these modes. B or B are used to enable the Bell 0T mode of operation.

3 AN_0 Using the M0CE in a KSeries Application B UA LVC0 R 0 UD LVC0 R 0 B B M0CE_MLF/TQFP 0 USR0 NG 0 OSCIN USR USR0 UB 0 LVC0 UC LVC0 B VCC_D VCC_D RJ B B B B RXA VBG TXAP TXAN VPA 0 C 0uF VCCA B B Figure. Configuration for Wire DialUp Half Duplex Operation Both commands set up the same mode and are interchangeable. B and B do the same for V.. These modes can be used when there are two physical channels for the data carriers. They cannot be used for wire applications or where the same physical link is used for sending signals in both directions. Using the AT@L command causes the modems to connect without going through the normal dialup handshake..0 MHz C pf Y C pf VCC_D B C 0.uF C.uF.V U 0CE_QFN/TQFP 0 USR0 NG 0 OSCIN USR USR0 C 0uF C 0.uF RXA VBG TXAP TXAN VPA 0 C 0uF VCC_D VCCA C0 0.uF C 0.uF C 0.uF C 0.uF R MIT T R MIT T WREC WREC WTX WTX C.uF.V C 0.uF C.uF,.V R K Figure. Using the M0 in a Wire Application A partial list of commands is shown in Table. Since leased line mode will not disconnect when the link is broken and it may not be desirable to use the escape character to go into the command mode to send a disconnect command, the R command is used to disconnect the modems while in leased line mode. This allows the de

4 AN_0 Using the M0CE in a KSeries Application assertion of to trigger the modem to return to the idle state. The C command is also used. C is used to make the (Data Carrier Detect) follow the raw, rather than qualified, carrier. Function 0CE Command Initialization String Vbis Leased Line FDX ATFYKCRS0=S0=SO@L V Leased Line FDX ATFYKCRS0=S0=@L Bell Leased Line FDX ATFYKCRS0=S0=@L Bell 0 Leased Line FDX ATFYKCRS0=S0=@L Bell 0 RX Leased Line HDX ATFY0CRBS0=@L Bell 0 TX Leased Line HDX ATFY0CRBS0=@L Bell 0 Wire Leased Line FDX ATFY0BCRS0=@L V Leased Line FDX ATFYKCRS0=S0=@L V. Wire Leased Line ATFY0BCRS0=@L V TX00 ATFYKCRBS0= V TX ATFYKCRBS0= SMS V. MODE HDX ATFY0B0SCRS0= Table. Partial list of Initialization Commands for Leased Line and FSK Modes If speed buffering is used (Y), flow control (K or K) must also be used. This prevents the modem input buffers from overflowing. Always have the DTE rate higher than the highest expected modulation rate for best performance. The DTE rate can be as high as. Kbps. K hardware flow control uses the and lines to control the data flow. K uses inband special characters that the modem recognizes to control the data flow. These are removed from the data stream automatically by equipment that supports XON/XOFF flow control. V. asymmetric FDX (TX00/RX or TX/RX00) should always be used with speed buffering and flow control for obvious reasons. The half duplex and wire modes usually are used in the clear channel, nonspeed buffered mode. V. SMS mode is a special mode that allows the modem to be used in V. Half Duplex. For details on SMS operation, please see the separate app note, M0CE SMS and Half Duplex V. Operation. The V.bis leased line mode is set up slightly differently than the others because it can retrain in case the connection degrades or the connection broken and a retrain is desirable. S0= lowers the retrain threshold slightly while S and the O command enable and allow retains automatically. If retrain is not desired, these can be left in their default states. M0CE ENERGY NG DETECTION The M0CE has a new feature that was added with the intention of lowering the total modem cost by eliminating some of the more expensive external components. While up dating to the M0CE is may be desirable to include this feature. The threshold for the ring detector depends on the setting of the S register and the components in the Caller ID path, especially the transformer. The number that S is set to represents the amplitude threshold of the ring signal. In a conventional ring detect circuit the threshold is set by the hardware, usually the values of the zener diodes in the ring detect circuit. US Wet Transformer S Register Setting w/ freq. Checking 0 0 Vrms min off to on Vrms min on to off 0 CTR Dry Transformer S Register Setting w/ freq. Checking 0 0 Vrms min off to on Vrms min on to off Table. Approximate Thresholds for Energy Ring Detection

5 AN_0 Using the M0CE in a KSeries Application Having the ability to set the threshold over a wide range through the S register eliminates the need to change components to adjust the ring detection sensitivity. Energy ring detection uses the Caller ID path and coupling transformer to path to pass the incoming ring signal to the modem so it can detect the ring signal using the internal DSP. In an average design this can save at least $0. in the total parts cost or even more in lower volume products. The M0CE is still compatible with the earlier 0 products and still supports the optoisolated ring detection method. Wet transformers generally have poorer frequency response in the ring frequency range than dry transformers. This means that the threshold must be sent to a lower number for wet transformers than with some V.0rated dry transformers. This also means that lower frequency ring signal detection will also require a lower setting. The range of values for S can be from to when checking frequency or to when not checking frequency. The practical range is from to 0 when checking frequency, depending on the transformer, Caller ID series resistor, capacitor, and the ring frequency. The other ring parameters such as ring frequency (S and S) and cadence (SS) still need to be programmed when using energy ring detection. CONCLUSION The M0CE is a versatile modem IC that can be used in a wide variety of applications and is the right choice for a replacement of KSeries devices in existing products. If you have questions about how to use it in your application, you can consult the TEDIAN Modem Applications Department for assistance. We are always here ready to help you with any TEDIAN modem product and can advise you of your choices and the best product match for your particular application. This product is sold subject to the terms and conditions of sale supplied at the time of order acknowledgment, including those pertaining to warranty, patent infringement and limitation of liability. TEDIAN Semiconductor Corporation (TSC) reserves the right to make changes in specifications at any time without notice. Accordingly, the reader is cautioned to verify that the data sheet is current before placing orders. TSC assumes no liability for applications assistance. TEDIAN Semiconductor Corp., 0 Oak Canyon Rd., Irvine, CA TEL () 000, FAX () 0, 00 TEDIAN Semiconductor Corporation 0//0 rev.