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a-229 contents ? introduction ? applications ? how it works ? a three pin interface ? general requirements ? data transmission methods and message formats ? application circuits using the MT8841 ? five function telephone line interface ? micro-controller parallel read ? micro-controller serial read ? multiple line cid card ? a final word introduction the purpose of this application note is to provide information on the operation and application of calling number identi?cation circuits. the MT8841 calling number identi?cation circuit (cnic) will be discussed in detail and its use illustrated in the application examples which follow. everyone, at some time, has rushed to answer a ringing phone only to have the caller hang up. we have all had a persistent salesman (or a talkative friend) call our of?ce or home and interrupt us at the wrong time. many of us have had to sit and listen to elevator music while someone on the other end of the line attempts to bring up information about our account. by allowing call screening and quick access to databases before the phone is answered, caller id (cid) promises a cure for many of the annoying telephone problems that beset us. in a caller id system, a coded version of the calling number is sent from the central of?ce to the called phone where it appears on a small liquid crystal display (lcd). for both residential and of?ce phones, the subscriber will know who is calling (provided it is a known number) and be able to screen the calls. in more sophisticated applications, when the line is connected to a computer, the computer can use the number to search a database and display information about the individual calling. issue 1 august 1993 msan-144 applications of the MT8841 calling number identi?cation circuit application note
msan-144 application note a-230 applications caller id technology has many commercial applications. for example, an insurance company could display all the relevant information about a client's policies even before the phone is answered, which would save time for both the company and the customer. a hospital might use this capability to bring up a patient's medical records when they call in. a mail order company could display the buying record of a customer and be ready to conduct business by the time the ?rst word is spoken. there are many cid implementations. the chip can be used in a small stand-alone unit (with an lcd) connected to the line, or it can be built into a telephone set. it can be used in a computer or on a trunk card in a pbx. there is a growing interest in cid from the companies that are designing the next generation of answering machines. the answering machine companies want to be able to identify and record the number of callers who hung up without leaving a message. in addition, answering machine users want to be able to program certain numbers that the user doesn't want to talk to so that these calls can be sent directly to the answering machine for recording and later reply. cid technology will also be incorporated in fax machines and combination fax/answering machines to allow users to screen for junk faxes. telephone companies view caller id as another service to generate revenue. consequently, the bell operating companies asked bell communications research (bellcore) to prepare speci?cations that show manufacturers how to build cid equipment. these describe features and functions of equipment or interfaces for possible use by any divested bell operating company or its regional af?liate. in the calling number delivery (cnd) service, the information about a calling party is embedded in the silent interval between the ?rst and second ring. besides cnd, there are other telephone company services that use the same transmission scheme. for example, another service extends cnd with call waiting so that customers can tell who is calling on the other line. this requires some handshaking between the phone and the central of?ce. future devices will incorporate this feature. calling name delivery (cnam), another service using the same scheme, displays the name of the caller, rather than the number. how it works the principle of cid is relatively simple. coded signalling information is sent during the period between the ?rst and second ring. continuous phase binary frequency shift keying (fsk) is used for coding. the cid chip decodes analog information and transforms it into a digital bit stream which is available at the data pin. a micro-controller extracts caller information from the digital stream. a cid system has ?ve important functions: line termination during data reception, high voltage isolation, common mode rejection, ring detection and cid data reception. these functions, with the exception of cid reception, are not built into most cid devices, so a small amount of external circuitry is required. the receive data dynamic range of the cid detection circuit is a critical requirement. on a long loop the signal strength may be very low, but the cid device must be able to detect it. consequently, analog performance as shown by the detect level and the ability to perform in the presence of noise is very important. the mitel calling number identi?cation circuit (cnic) for example, has a detect level of - 36dbm, speci?ed over the entire temperature range. the device is also speci?ed to operate at a typical 20db s/n ratio. in addition, the MT8841 has a user accessible input op-amp which can be con?gured in a differential mode to reduce the effects of common mode noise. the input gain may also be changed easily (either increased or decreased) to meet speci?c regulatory decode level requirements. this is accomplished by changing the resistor values of the input op-amp network. according to the bellcore speci?cations, the customer premises equipment (cpe) should terminate the transmission line with the correct impedance while data is being transmitted. the cpe must detect the end of the ?rst power ring and switch in the termination. the termination is external to the cid chip and is typically connected with a relay during the period between the ?rst and second ring signals. for applications requiring reduced power consumption, a power down mode is desirable. the MT8841 has a power down pin (pwdn), which when pulled high, forces the device into power down. this is typically done after receiving a message. in this mode, the cid device ceases to function and the chip will not react to an input signal. pulling the pin to ground wakes up the chip so that it can receive the fsk signal and start decoding.
application note msan-144 a-231 a three-pin interface most cid devices only provide a single pin from which the received data is sent to the micro- controller. consequently, the data stream appearing at the serial data output must be converted to 8-bit words by a uart (universal asynchronous receiver transmitter). the mitel cnic, however, has three pins dedicated to the user interface. this eliminates the need for a uart or the high software overhead of a micro-controller performing the uart function (asynchronous serial data reception). refer to the MT8841 data sheet and figure 1 below. general requirements for calling number delivery service according to the bellcore technical reference tr- nwt-000030, the central of?ce physical layer interface has the following parameters for providing cnd service: link type: two wire, half-duplex from spcs to cpe modulation type: continuous-phase binary fsk logical 1 (mark) : 1200 12 hz logical 0 (space): 2200 22 hz transmission rate: 1200 12 baud signal level: -13.5 dbm 1.5db at the point of application to the loop facility into a resistive load of 900 ohms. source impedance: 900 ohms in series with 2.16 m f to meet return loss requirements speci?ed in tr- tsy-000507. application of data: serial, binary, asynchronous to properly interact with spcs for both on-hook and off-hook data transmission schemes, the cpe should receive a data signal that meets the following parameters: ? link type, modulation type, transmission rate, application of data, logical 1 (mark) and logical 0 (space): same as central of?ce transmit values shown above. ? received signal level at 1200 hz: between -32 dbm and -12.5 dbm. ? received signal level at 2200 hz: between -36 dbm and -12.5 dbm. ? signal to distortion ratio: > 25 db. figure 1 - serial data interface timing b0 b1 b2 b3 b4 b5 b6 b7 0 1 b7 b0 b1 b2 b3 b4 b5 b6 b7 b7 b0 b1 b2 b3 b4 b5 b6 b7 0 1b0b1b2 0 1 b0 b1 b2 b3 b4 b5 b6 b7 b0 b1 b2 tip/ring data dclk dr * stop start stop start stop start stop start stop start stop start * with external pull-up resistor
msan-144 application note a-232 data transmission methods and message formats the cnic can process a fsk modulated signal carrying information compatible with any of the three data transmission methods speci?ed by tr-nwt- 000030: ? on-hook data transmission associated with ringing, ? on-hook data transmission not associated with ringing, ? off-hook data transmission. the spcs data interface supports single data message and multiple data message formats. in the single data message format, information is sent to the cpe as a series of data words specifying message type, message length, message data and error detection information. in the multiple data message format, information sent to the cpe is similar to the single message format except the message data ?eld is replaced by a series of parameter messages. each parameter message consists of data words specifying parameter type, parameter length and parameter data. for single and multiple data message formats each word shall consist of an 8-bit data byte preceded by a start bit (space) and followed by a stop bit (mark). the least signi?cant bit of each data byte shall be transmitted ?rst. the mark bits (maximum ten bits of high) may also be inserted between message words when necessary. since the fsk modulation is used in both data message formats, the differences between the two formats are transparent to the cnic. brie?y, the cnd multiple data message format consists of the following: field (1): the channel seizure signal, used for on- hook data transmission only, is a block of 300 continuous bits of alternating "0"s and "1"s. the ?rst bit to be transmitted is "0" while the last bit is "1". field (2): the mark signal is composed of 80 10 bits of continuous high. field (3): 1 byte of message type word. field (4): the message length is the 1-byte information that speci?es the total number of message data words (for single data message format) or parameter words (multiple data message format) sent to the cpe, excluding the ?nal checksum. field (5): parameter messages can consist of n parameters and each parameter is further divided into three sub-?elds in the order shown below: parameter type word (1 byte) speci?es the interpretation of the sub-?eld parameter data words. possible message types include: time, dialable directory number (ddn), absence of ddn and call quali?er. parameter length word (1 byte) equals the number of data bytes contained in the parameter data words sub-?eld. parameter data words possible data words include: date, time, incoming call number and reason for absence of ddn. note all data bytes in this sub-?eld are encoded in ascii format. field (6): 1 byte binary checksum = 2's complement of {?eld (3) + ?eld (4) + ?eld (5)} mod 256. mk: mark bits (0-10) application circuits using the MT8841 five function telephone line interface the telephone line interface in figure 2 performs ?ve basic functions, mentioned previously. it terminates the line with 600 ohms, provides high voltage isolation, provides common mode rejection with a differential input, detects ringing, and converts the calling number fsk signal to a serial data format. during fsk signal reception, the line must be terminated with 600 ohms ac coupled. a termination circuit with relay and relay driver is typically used for channel seizure signal (1) mark signal (2) message type word (3) message length word (4) parameter messages (5) check sum word (6)
application note msan-144 a-233 figure 2 - line interface with protection, termination and ring detector tip ring k1 c1 r1 r2 c2 r3 r5 r4 r6 d5 d4 d6 c3 earth ground internal ground r7 in+ in- gs vref vss k1 d1 q1 r10 r8 r9 MT8841 relay rd u2b vdd vdd d3 u1 r11 c4 d2 r12 r13 c5 components list: u1 u2 d2, d1 d3, d4, d5, d6 q1 c2, c3 c5 c4 c1 r10 4n25, opto-coupler 74hc14, inverter schitt hex in4004, 400v 1a, rectifier general in5245b, 15v 1/2w, zener general 2n3904, 40v 200ma, transistor npn 0.022 m , 400v 5%, capacitor polyester 0.33 m , 50v 20%, capacitor ceramic 0.33 m , 250v 5%, capacitor polyester 2 m 2, 250v 5%, capacitor polyester 1k, 1/2w 1%, resistor metal r5, r6 r7 r8 r13 r12 r9 r1 r11 r2, r3, r4 k1 34k, 1/2w 1%, resistor metal 53k6, 1/2w 1%, resistor metal 60k4, 1/2w 1%, resistor metal 140k, 1/2w 1%, resistor metal 301k, 1/2w 1%, resistor metal 464k, 1/2w 1%, resistor metal 600r, 1/2w 5%, resistor fusible 12k, 1w5 5%, resistor fusible 430k, 3w 5%, resistor power 1kv rdpdt, 5v 28ma, relay dpdt u2a this function as shown in fig. 2. when relay k1 is activated (during data reception), the telephone line is terminated with 600 w (r1) and 2.2 m f (c1). a 430k resistor (r2) ensures that capacitor c1 is biased with the 48v co (central of?ce) battery voltage when relay k1 is not activated. this reduces undesirable transients when the termination circuit is activated. the high impedance isolation circuit protects the user and the low voltage circuitry from high voltage fault conditions which may occur on the line. the high power resistors and high voltage capacitors (c2, c3, r3, r4), were selected to meet most line fault conditions. the high impedance components limit the current, while the zener's (d4, d5, d6) limit the voltage. relay k1 and opto-coupler u1 also provide physical isolation. in the ringing detector of figure 2, the ringing response is determined mainly by the charge time of c5 through r13, as well as the positive going threshold of the cmos schmitt trigger. the ringing detector decay time is determined mainly by the discharge time of c5 through r12 and r13, as well as the negative going threshold of the cmos schmitt trigger. typical response time is 150ms and typical decay time is also 150ms. the fsk signal data is input to the MT8841 through a differential ampli?er con?guration with overall gain of unity. to increase the common mode rejection range, a modi?ed differential input con?guration is used. a voltage divider of r7 (53.6k) and r3 + r5 (464k) reduces the op-amp signal at the positive input by 9.66 times. to maintain an overall gain of 1, the attenuation due to the voltage divider must be cancelled. this is achieved by increasing the op- amp gain to 9.66. therefore, 9.66 = 1 + r9/(r8// (r4+r6)); with r9 at 464k, r8 is 60.4k. since the op-amp common mode range is 3vpp, the maximum common mode input signal that this circuit can cancel is 3vpp 9.66 = 29vpp = 10.2vrms.
msan-144 application note a-234 figure 3 - logic controller and dce interface vdd r1 c1 rx/cs cx a rd relay q qm u1a u3a u4a vdd vdd r2 cd d ck cl q qf u5a u5b vdd c2 c3 transmit (rs-232) dcd (rs-232) data pwdn cd MT8841 notes: 1. decoupling not shown. 2. u1-4 powered from +5v. 3. u5 powered from 12v. components list: u1 u2 u3 u4 u5 r1 r2 c1 c2, c3 74hc123, mmv retriggerable dual 74hc74, d flip-flop dual 74hc00, nand 2ip quad 74hc04, inverter hex mc1488, rs-232 line driver quad 820k, 1/2w 1%, resistor metal 10k, 1/2w 1%, resistor metal 10 m , 63v 20%, capacitor electrolytic 330p, 50v 20%, capacitor ceramic u2a normally, the device is powered down, but during fsk signal reception, it is powered up. a discrete logic solution is shown in fig. 3 which provides the relay termination ( rela y) and the MT8841 powerdown (pwdn) control signals during the period between the ?rst and second ringing bursts. the above two logic signals are generated by four integrated circuits (u1 to u4). input signals to the controller are from the ringing detector ( rd), and cnic carrier detect ( cd) outputs. the timing diagram for the logic controller is shown in fig. 4. since the relay termination is activated by the ?rst carrier detection following the ringing signal, the circuit will also function correctly for distinctive ringing, where two quick ringing bursts are followed by the fsk. the start of a ringing burst is signalled by the falling edge of the ring detector ( rd) output. this triggers the monostable multivibrator (mmv) which generates an 8 second output pulse at qm that powers up the cnic. shortly after the ?rst ringing burst, the central of?ce (co) sends the fsk signal. the cnic detects this and the carrier detect output ( cd) goes low, this activates the termination relay. the end of fsk transmission is signalled with cd going to logic high. this clocks the ?ip ?op resulting in a logic low at the qf output. this deactivates the termination relay which cannot be re-activated until ringing is once again detected followed by a carrier detect signal. in the rs-232 dce line driver (fig. 3), serial data (data) and the carrier detect signal ( cd) from the MT8841 are converted to rs-232 levels and provided as outputs (transmit and dcd). these may be directly connected to a dce such as a personal computer with appropriate software. micro-controller parallel read the cnic micro-controller interface (fig. 5) is a symbolic circuit showing a micro-controller performing both the logic functions of fig. 3 and the data handling. the cnic provides serial data (data), data clock (dclk), and data ready ( dr) signals that can be used to easily convert data from a serial stream to a parallel stream (see fig. 1). conversion is accomplished by connecting the serial data and clock lines to an external shift register like a 74hc164. when the data ready line alerts the micro-controller with an interrupt, it reads the shift register's 8-bit parallel output. only the 8-bit character information of the 10-bit word is converted, since the dclk remains high for both stop and start bits. the data ready signal indicates the reception of every 10-bit word sent from the central of?ce.
application note msan-144 a-235 figure 4 - logic controller timing 1 ring cycle = 6 sec 2 sec on 4 sec off off-hook tip/ring rd cd (cnic) pwdn (mmv qm) qf (flip flop) rela y first ringing signal fsk signal second ringing signal voices 30 ms typical 1 4 6 10 2 0 3 5 7 8 9 11 12 13 notes: the objective is to apply the termination impedance between the first and second ringing bursts; during the fsk signal. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 flip flop is in unknown state. ringing is detected, rd goes low. mmv is triggered, cnic is powered up. flip flop is reset by rd at low. carrier is detected, cd goes low. relay goes low due to qf high and cd low. carrier is ended, cd goes high. flip flop is clocked by cd going high, qf goes low. relay goes high due to qf low or cd high. flip flop is reset, qf goes high. voice is detected, cd toggles between low and high. relay momentarily goes low due to qf high and cd low. flip flop is clocked by cd going high, qf goes low and remains low until ringing is detected. mmv times out, qm returns to high, cnic is powered down. micro-controller serial read in another interfacing method (not shown here), data and dclk are connected directly to two inputs of a micro-controller port, and dr is connected to the interrupt input. this eliminates the serial to parallel shift register but increases the complexity of the software. in this con?guration, the micro-controller polls the dclk bit and stores the data value on every dclk low to high transition. dclk toggles high eight times for each character. when dr pulses low, it marks the end of the 8-bit character (and 10-bit word). multiple line cid card another advantage of the three pin interface is that it is easy to use in applications where multiple cid chips are required on the same card. this card could, for example, be used in a pbx so that a cid device needn't be built into every phone in the building. this would also permit the use of existing display station sets. in such a system, the number of cnic's could equal the number of incoming lines from the central of?ce. since the number of incoming lines is much smaller than the number of station lines, the total number of cnic's required for a system can be greatly reduced. this cnic card could have many cnic's with only a single inexpensive micro-controller used to convert the
msan-144 application note a-236 figure 5 - micro-controller and serial-to-parallel converter data dclk dr pwdn r1 r2 vdd a ck qa qb qc qd qe qf qg qh MT8841 u1 cd relay rd micro-controller d7 d6 d5 d4 d3 d2 d1 d0 d7 d6 d5 d4 d3 d2 d1 d0 p1.0 p1.1 p1.2 p1.3 p1.4 p1.5 p1.6 p1.7 p2.0 p2.1 p2.2 int1 int0 components list: u1 r1,2 74hc164 serial-to-parallel shift register 10k, 1/2w 1%, resistor metal notes: 1. 2. 3. decoupling not shown. u1 powered from +5v. the micro-controller is symbolic and circuitry may vary depending upon micro selected. code for the caller identi?cation for all of the chips, and no uarts would be required. the micro- controller would then pass on the data to the receiving station set according to the pbx protocol. in this cnic card application, all dr signals are tied into a single interrupt on the micro-controller. each cnic data and dr output is connected into a serial to parallel shift register with a tri-state output enable. the tri-state outputs are all bussed together and connected to an input port of the micro-controller. all shift register tri-state output enables are driven by an output port. all dr signals are also input to another input port. upon receiving an interrupt, the micro- controller polls the dr lines to determine which cnic has delivered data to its shift register. the micro-controller then enables the tri-state output corresponding to the activated dr and reads the 8 bit data at its input port (see fig. 6) a final word caller id and related technologies will open up many new applications for both telephone companies and their customers. the technology promises to help us gain control over the telephone instead of it controlling us. best of all, the technology is relatively simple and easily implemented, using the inexpensive devices now available on the market.
application note msan-144 a-237 figure 6 - multiple line cid card line 1 line 2 line 8 u1 u2 u8 u11 u12 u18 u21 u22 u28 micro-controller MT8841 MT8841 MT8841 data dclk dr dr0 qa qb qc qd qe qf qg qh a ck qa qb qc qd qe qf qg qh a ck qa qb qc qd qe qf qg qh a ck data dclk dr dr1 data dclk dr dr7 8 dr0 dr7 u30 cs0 cs1 cs7 d7 d6 d5 d4 d3 d2 d1 d0 d7 d6 d5 d4 d3 d2 d1 d0 d7 d6 d5 d4 d3 d2 d1 d0 d7 d6 d5 d4 d3 d2 d1 d0 cs0 cs1 cs2 cs3 cs4 cs5 cs6 cs7 dr0 dr1 dr2 dr3 dr4 dr5 dr6 dr7 p0.0 p0.1 p0.2 p0.3 p0.4 p0.5 p0.6 p0.7 p1.0 p1.1 p1.2 p1.3 p1.4 p1.5 p1.6 p1.7 p2.0 p2.1 p2.2 p2.3 p2.4 p2.5 p2.6 p2.7 int0 notes: 1. the micro-controller is symbolic and circuitry may vary depending upon micro selected. 2. port 2.x has pull-up resistors. 3. decoupling not shown. 4. power not shown. components list: u1-8 u11-18 u21-28 u30 MT8841 cnic 74hc164 serial-to-parallel shift register 74hc241 octal tri-state buffer 74hc30 8 input nand gate
msan-144 application note a-238 notes:
m mitel (design) and st-bus are registered trademarks of mitel corporation mitel semiconductor is an iso 9001 registered company copyright 1999 mitel corporation all rights reserved printed in canada technical documen t a tion - n o t for resale world headquarters - canada tel: +1 (613) 592 2122 fax: +1 (613) 592 6909 north america asia/paci?c europe, middle east, tel: +1 (770) 486 0194 tel: +65 333 6193 and africa (emea) fax: +1 (770) 631 8213 fax: +65 333 6192 tel: +44 (0) 1793 518528 fax: +44 (0) 1793 518581 http://www.mitelsemi.com information relating to products and services furnished herein by mitel corporation or its subsidiaries (collectively mitel) is believed to be reliable. however, mitel assumes no liability for errors that may appear in this publication, or for liability otherwise arising from the application or use of any such information, product or service or for any infringement of patents or other intellectual property rights owned by third parties which may result from such application or use. neither the supply of such information or purchase of product or service conveys any license, either express or implied, under patents or other intellectual property rights owned by mitel or licensed from third parties by mitel, whatsoever. purchasers of products are also hereby noti?ed that the use of product in certain ways or in combination with mitel, or non-mitel furnished goods or services may infringe patents or other intellectual property rights owned by mitel. this publication is issued to provide information only and (unless agreed by mitel in writing) may not be used, applied or reproduced for any purpose nor form part of any order or contract nor to be regarded as a representation relating to the products or services concerned. the products, their speci?cations, services and other information appearing in this publication are subject to change by mitel without notice. no warranty or guarantee express or implied is made regarding the capability, performance or suitability of any product or service. information concerning possible methods of use is provided as a guide only and does not constitute any guarantee that such methods of use will be satisfactory in a speci?c piece of equipment. it is the users responsibility to fully determine the performance and suitability of any equipment using such information and to ensure that any publication or data used is up to date and has not been superseded. manufacturing does not necessarily include testing of all functions or parameters. these products are not suitable for use in any medical products whose failure to perform may result in signi?cant injury or death to the user. all products and materials are sold and services provided subject to mitels conditions of sale which are available on request.

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