8870 app

7/27/2019 8870 App

1/23A-45

Contents

DTMF Receiver Development

Mobile Radio Applications

Inside The MT8870

Distributed Control Systems

DTMF Receiver Application

Data Communication Using DTMF

Introduction

The purpose of this Application Note is to provideinformation on the operation and application ofDTMF Receivers. The MT8870 Integrated DTMFReceiver will be discussed in detail and its useillustrated in the application examples which follow.

More than 25 years ago the need for an improvedmethod for transferring dialling information throughthe telephone network was recognized. Thetraditional method, Dial pulse signalling, was not onlyslow, suffering severe distortion over long wire loops,but required a DC path through the communicationschannel. A signalling scheme was developed

utilizing voice frequency tones and implemented as avery reliable alternative to pulse dialling. Thisscheme is known as DTMF (Dual Tone Multi-Frequency), Touch-Tone or simply, tone dialling.As its acronym suggests, a valid DTMF signal is thesum of two tones, one from a low group (697-941Hz)and one from a high group (1209-1633Hz) with eachgroup containing four individual tones. The tone

frequencies were carefully chosen such that they are

not harmonically related and that theirintermodulation products result in minimal signallingimpairment (Fig. 1a). This scheme allows for 16unique combinations. Ten of these codes representhe numerals zero through nine, the remaining six(*,#,A,B,C,D) being reserved for special signallingMost telephone keypads contain ten numeric pushbuttons plus the asterisk (*) and octothorp (#). Thebuttons are arranged in a matrix, each selecting itslow group tone from its respective row and its highgroup tone from its respective column (Fig. 1b).

The DTMF coding scheme ensures that each signa

contains one and only one component from each ofthe high and low groups. This significantly simplifiesdecoding because the composite DTMF signal maybe separated with bandpass filters, into its two singlefrequency components each of which may behandled individually. As a result DTMF coding hasproven to provide a flexible signalling scheme ofexcellent reliability, hence motivating innovative andcompetitive decoder design.

Development

Early DTMF decoders (receivers) utilized banks ofbandpass filters making them somewhatcumbersome and expensive to implement. Thisgenerally restricted their application to central offices(telephone exchanges).

The first generation receiver typically used LC filtersactive filters and/or phase locked loop techniques to

Figure 1a - The Dual Tone Multifrequency (DTMF) Spectrum

685 709 756 784 837 867 925 957 1189

1358 1501 16591229

1314 1453 1607

697 770 852 941 1209 1336 1477 1633

2 dB

Tones generated from a telephone typically have -2 dB twist

(pre-emphasis) applied to compensate for high frequency

roll off along the telephone line.AMPLITUDE

f (Hz)

logarithmic

Standard DTMF frequency spectrum (1.5% + 2 Hz). Second harmonics of the low group (possiblycreated due to a non-linear channel) fall within the passband of the high group (Indicated by A,B,C,D).This is a potential source of interference.

A B C D

ISSUE 1 June 1983

MSAN-108Application NoteApplications of The MT8870

Integrated DTMF Receiver

7/27/2019 8870 App

2/23

MSAN-108 Application Note

A-46

Figure 1b - The Dual Tone Multifrequency (DTMF) Keypad

Figure 2 - Typical DTMF Receiver Applications

LOW GROUP

TONES

LEGEND :

H1 =1209

Hz

H2 =1336Hz

H3 =1477Hz

H4 =1633Hz

HIGH GROUP TONES

L1 = 697 Hz

L2 = 770 Hz

L3 = 852 Hz

L4 = 941 Hz

DTMF signal not available on a standard

pushbutton telephone keypad

1

4

7

*

2

5

8

0

3

6

9

#

A

B

C

D

Telephone DTMF keypad matrix. Column H4 is normally not available on a telephone keypad and isreserved for special signalling.

LOOP CURRENT

DETECT CIRCUIT

DISCONNECT

RELAY

MT8870

DTMF

RECEIVER

DECODE

LOGIC

CIRCUIT

RELAY

DRIVER

RINGING

DETECTOR

RESET

LOGIC

DISABLE

LOGIC

TO TELEPHONE

EXCHANGE

RECTIFIER

FILTER

VDD

& REGULATOR

a) Block diagram of a toll call restrictor. This could be implemented on a small pc board and installedin a telephone to disallow long distance calling.

LINE INTERFACELINE SPLIT RELAY

LINE INTERFACE

CONTROL

LOGICMT8870

DTMF

RECEIVER

MT4325

PULSE

DIALER

CENTRAL TELEPHONE SWITCHING OFFICE

TOSTEP-BY-STEP

EXCHANGE

b) Block diagram of a simple tome to pulse converter to allow TOUCH-TONE dialing into a step-by-step or crossbar exchange.

7/27/2019 8870 App

3/23

Application Note MSAN-108

A-47

receive and decode DTMF tones. Initial functionswere, commonly, phone number decoders and tollcall restrictors. A DTMF receiver is also frequentlyused as a building block in a tone-to-pulse converterwhich allows Touch-Tone dialling access tomechanical step-by-step and crossbar exchanges(Fig. 2).

The introduction of MOS/LSI digital techniquesbrought about the second generation of tone receiverdevelopment. These devices were used to digitallydecode the two discrete tones that result fromdecomposition of the composite signal. Two analogbandpass filters were used to perform thedecomposition.

Totally self-contained receivers implemented in thickfilm hybrid technology depicted the start of thirdgeneration devices. Typically, they also used analogactive filters to bandsplit the composite signal and

MOS digital devices to decode the tones.

The development of silicon-implemented switchedcapacitor sampled filters marked the birth of thefourth and current generation of DTMF receivertechnology. Initially single chip bandpass filters werecombined with currently available decoders enablinga two chip receiver design. A further advance inintegration has merged both functions onto a singlechip allowing DTMF receivers to be realized inminimal space at a low cost.

The second and third generation technologies saw atendency to shift complexity away from the analogcircuitry towards the digital LSI circuitry in order toreduce the complexity of analog filters and theirinherent problems. Now that the filters themselvescan be implemented in silicon, the distribution ofcomplexity becomes more a function of performanceand silicon real estate.

Inside The MT8870

The MT8870 is a state of the art single chip DTMFreceiver incorporating switched capacitor filter

technology and an advanced digital counting/averaging algorithm for period measurement. Theblock diagram (Fig. 3) illustrates the internalworkings of this device.

To aid design flexibility, the DTMF input signal isfirst buffered by an input op-amp which allowsadjustment of gain and choice of input configuration.The input stage is followed by a low pass continuousRC active filter which performs an antialiasingfunction. Dial tone at 350 and 440Hz is then rejectedby a third order switched capacitor notch filter. The

signal, still in its composite form, is then split into itsindividual high and low frequency components bytwo sixth order switched capacitor and pass filters.Each component tone is then smoothed by an outputfilter and squared up by a hard limiting comparator.

The two resulting rectangular waves are applied todigital circuitry where a counting algorithm measures

and averages their periods. An accurate referenceclock is derived from an inexpensive externa3.58MHz colourburst crystal.

The timing diagram (Fig. 4) illustrates the sequenceof events which follow digital detection of a DTMFtone pair. Upon recognition of a valid frequency fromeach tone group the Early Steering (ESt) output israised. The time required to detect the presence otwo valid tones, tDP, is a function of the decodealgorithm, the tone frequency and the previous stateof the decode logic. ESt indicates that two tones of

proper frequency have been detected and initiatesan RC timing circuit. If both tones are present for theminimum guard time, tGTP, which is determined bythe external RC network, the DTMF signal isdecoded and the result ing data (Table 1) is latched inthe output register. The Delayed Steering (StD)output is raised and indicates that new data isavailable. The time required to receive a valid DTMFsignal, tREC , is equal to the sum of tDP andtGTP.

Table 1. MT8870 Output Truth Table0=LOGIC LOW 1=LOGIC HIGH Z=HIGH IMPEDANCE

Output truth table. Note that key "0" is output as "1010 2(ie:1010)" corresponding to standard telephony coding.

A simplified circuit diagram (Fig. 5) illustrates howthe chips steering circuit drives the external RCnetwork to generate guard times. Pin 17, St/GT(Steering/Guard Time), is a bidirectional signal pinwhich controls StD, the output latches, and resetsthe timing circuit. When St/GT is in its input mode(St function) both Q1 and Q2 are turned off and thevoltage level at St/GT is compared to the steeringthreshold voltage VTSt. A transition from below toabove VTSt will switch the comparators output from

fLOW fHIGH KEY TOE Q4 Q3 Q2 Q1

697 1209 1 1 0 0 0 1697 1336 2 1 0 0 1 0

697 1477 3 1 0 0 1 1770 1209 4 1 0 1 0 0770 1336 5 1 0 1 0 1770 1477 6 1 0 1 1 0852 1209 7 1 0 1 1 1852 1336 8 1 1 0 0 0852 1477 9 1 1 0 0 1941 1209 0 1 1 0 1 0941 1336 * 1 1 0 1 1941 1477 # 1 1 1 0 0697 1633 A 1 1 1 0 1770 1633 B 1 1 1 1 0852 1633 C 1 1 1 1 1941 1633 D 1 0 0 0 0

- - ANY 0 Z Z Z Z

7/27/2019 8870 App

4/23


A-48

Figure3-

MT8870FunctionalBlockDiag

ram

INPUT

SIGNAL

VREF

GS

IN-

IN+

VDD

VSS

BIAS

CIRCUIT

- +

CHIPBIAS/POWER

CHIPREF.VOLTAGE

AN

TI-

ALIASING

FILTER

2ndO

RDER

CONT.RC

D

IALTONE

FILTER

3

50/440Hz

N

OTCHES

3

rdO

RDER

SW.CAP.

HIGH

GROUP

BANDPASS

FILTER

6thO

RDER

SWITCHED

CAPACITOR

LOW

GROUP

BANDPASS

FILTER

6thORDER

SWITCHED

CAPACITOR

CHIP

CLOC

K

OSC1

OSC2

VDD

TO

E

St/GT

ESt

StD

St

GT

STEERINGLOGIC

DIGITAL

DETECT

CIRCUIT

CODE

CON-

VERTER

AND

OUTPUT

LATCHES

MT8870

Q1

Q2

Q3

Q4

Externalguardtime,input,and

clockcomponents(dashed)areincludedfo

rclarity.

7/27/2019 8870 App

5/23


A-49

low to high strobing new data into the output latches,and raising the StD output. As long as an input levelabove VTSt is maintained StD will remain highindicating the presence of a valid DTMF signal.

Initially, when no valid tone-pairs are present,capacitor C is fully charged applying a low voltage toSt/GT. This causes a low at the comparators output

and since ESt is also low, Q2 turns on ensuring thatC is completely charged. In this condition St/GT is inits output mode (GT function). When a valid tone-pair is received ESt is raised turning off Q2 whichputs St/GT in its high impedance input mode andallows C to discharge through R. If this condition

persists for the tone-present guard time, tGTP, thevoltage at St/GT rises above VTSt raising StD whichindicates reception of a valid DTMF signal. If thetone pair drops out before the duration of tGTP, ESt islowered turning on Q2 which charges C resetting thetone-present guard time.

Once a DTMF signal is recognized as valid both ESt

and the comparator output are high. This turns onQ1 which discharges C and initializes the tone-absent guard time, tGTA. After the DTMF signal isremoved, ESt is lowered, Q1 turns off placing St/GTin its input mode and C begins to charge through R.

Figure 4 - MT8870 Timing Diagram

EXPLANATION OF EVENTS

EXPLANATION OF SYMBOLS

A) TONE BURSTS DETECTED, TONE DURATION INVALID, OUTPUTS NOT UPDATED.

B) TONE #n DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN OUTPUTS

C) END OF TONE #n DETECTED, TONE ABSENT DURATION VALID, OUTPUTS REMIAN LATCHED UNTIL NEXT VALID TONE.

D) OUTPUTS SWITCHED TO HIGH IMPE DA NCE STATE.

E) TONE #n + 1 DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN OUTPUTS (CURRENTLY HIGH IMPEDANCE).

F) ACCEPTABLE DROPOUT OF TONE #n + 1, TONE ABSENT DURATION INVALID, OUTPUTS REMAIN LATCHED.

G) END OF TONE #n + 1 DETECTED, TONE ABSENT DURATION VALID, OUTPUTS REMAIN LATCHED UNTIL NEXT VALID TONE.

Vin DTMF COMPOSITE INPUT SIGNAL.

ESt EARLY STEERING OUTPUT. INDICATES DETECTION OF VALID TONE FREQUENCIES.St/GT STEERING INPUT/GUARD TIME OUTPUT. DRIVES EXTERNAL RC TIMING CIRCUIT.

Q1-Q4 4-BIT DECODED TONE OUTPUT.

StD DELAYED STEERING OUTPUT. INDICATES THAT VALID FREQUENCIES HAVE BEEN PRESENT/ABSENT FOR THE REQUIRED GUARD TIME THUSCONSTITUTING A VALID SIGNAL.

TOE TONE OUTPUT ENABLE (INPUT). A LOW LEVEL SHIFTS Q1-Q4 TO ITS HIGH IMPEDANCE STATE.

tREC MAXIMUM DTMF SIGNAL DURATION NOT DETECED AS VALID

tREC MINIMUM DTMF SIGNAL DURATION REQUIRED FOR VALID RECOGNITION

tID MAXIMUM TIME BETWEEN VALID DTMF SIGNALS.

tDO MAXIMUM ALLOWABLE DROP OUT DURING VALID DTMF SIGNAL.

tDP TIME TO DETECT THE PRESENCE OF VALID DTMF SIGNALS.

tDA TIME TO DETECT THE ABSENCE OF VALID DTMF SIGNALS.

tGTP GUARD TIME, TONE PRESENT.

tGTA GUARD TIME, TONE ABSENT.

Vin

ESt

St/GT

Q1-Q4

StD

TOE

EVENTS A B C

D

E F G

tREC tREC tID tDO

TONE #nTONE#n + 1

TONE#n + 1

tDP tDA

tGTP tGTA

tPQtQStD

tPSrD

tPTD

tPTE

# n # (n + 1)HIGH IMPEDANCE

DECODED TONE # (n-1)

VTSt

7/27/2019 8870 App

6/23


A-50

Figure 5 - MT8870 Steering And GuardTime Circuit Operation

Valid tone presentindication fromDIGITAL DETECTcircuit.

To OUTPUTLATCHES

COMP.

+

-

MT8870

VTSt

VSS

n Q2

VDD

St/GT

ESt

(18)

(17)

(16)

StD (15)

VDD

C

R

A logical HIGH indicates that avalid signal is being receved.

p Q1

DELAY

STEERING TRUTH TABLE

0

0

1

1

VTStVTSt

0

Z

Z

1

0

1

0

1

ESt St(/GT) (St/)GT StD0 - LOGIC LOW1 = LOGIC HIGH

Z = HIH IMPEDANCE

VTSt = Threshold Voltqae

(typically 1/2 VDD)

Simplified steering circuit. Initially ESt is low, C is fully charged applying 0V to St/GT and Q2 is on. Upon reception of a valid tonepair ESt is raised turning off Q2 and allowing C to discharge through R which increases the voltae at St/GT. When VTSt is reachedthe comparator output goes high indicating a valid signal, latches the outputs and turns on Q1 which discharges C. When the tonepair is lost ESt goes low Q1 turns off and C charges through R decreasing the voltage at St/GT. When VTSt is reached StD goes lowand Q2 turns on resetting the timing circuit.

Steering circuit truth table. Note that pin 17 (St/GT) acts as both an input and an output depending on the relative states of EStand the comparator output.

If the same valid tone-pair does not reappear beforetGTA then the voltage at St/GT falls below VTSt which

resets the timing circuit via Q2 and prepares thedevice to receive another signal. If the same validtone-pair reappears before tGTA, ESt is raised turningon Q1 and discharging C which resets tGTA. In thiscase StD remains high and the tone dropout isdisregarded as noise.

To provide good reliability in a typical telephonyenvironment, a DTMF receiver should be designed torecognize a valid tone-pair greater than 40mS induration and, to accept as successive digits, tone-pairs that are greater than 40mS apart. However in

other environments, such as two-way radio, theoptimum tone duration and intra-digit times may

differ due to noise considerations.

By adding an extra resistor and steering diode (Fig.6b, 6c) tGTP and tGTA can be set to different values.Guard time adjustment allows tailoring of noiseimmunity and talk-off performance to meet specificsystem needs.

Talk-off is a measure of errors that occur when thereceiver falsely detects a tone pair due to speech orbackground noise simulating a DTMF signal.Increasing tGTP improves talk off performance since

7/27/2019 8870 App

7/23


Figure 6 - Guard Time Circuits

VDD

VDD

St/GT

ESt

R

R1 R2

C

MT8870

VDD

VDD

St/GT

ESt

MT8870

C

R1 R2

VDD

VDD

St/GT

ESt

MT8870

C

tGTP = (RC)In(VDD/VTSt)tGTA = (RC)In(VDD/[VDD-VTSt])

(a) (b)

[tGTP > tGTA]

tGTP = (R1C)In(VDD/VTSt)

tGTA = (RPC)In(VDD/[VDD-VTSt])

RP = R1R2/(R1 + R2)

[tGTP < tGTA]

tGTP = (RPC)In(VDD/VTSt)

RP = R1R2 (R1 + R2)tGTA = (R1C)In(VDD/[VDD-VTSt])

a) Tone present and absent guardtimes equal.

b) Tone present less than toneabsent guard time.

c) Tone present greater than toneabsent guard time.

Note: Typically VTSt = VDD1

2

(c)

it reduces the probability that speech will maintainDTMF simulation long enough to be consideredvalid. The trade-off here is decreased noiseimmunity because dropout (longer than tDA) due tonoise pulses will restart tGTP. Therefore, for noisy

environments, tGTP should be decreased. The signalabsent guard time, tGTA, determines the minimumtime allowed between successive DTMF signals. Adropout shorter than tGTA will be considered noiseand will not register as a successive valid tonedetection. This guards against multiple reception ofa single character. Therefore, lengthening tGTA willincrease noise immunity and tolerance to thepresence of an unwanted third tone at the expenseof decreasing the maximum signalling rate.

The intricacies of the digital detection algorithm have

a significant impact on the overall receiverperformance. It is here that the initial decision ismade to accept the signal as valid or reject it asspeech or noise.

Trade-offs must be made between eliminating talk offerrors and eliminating the effects of unwanted thirdtone signals and noise. These are mutuallyconflicting events. On one hand valid DTMF signalspresent in noise must be recognized which requiresrelaxation of the detection criteria. On the otherhand, relaxing the detection criteria increases the

probability of receiving "hits" due to talk off errors.

Many considerations must be taken into account evaluating criteria for noise rejection. In thtelephony environment two sources of noise apredominant. These are, third tone interferencwhich generally comes from dial tone harmonic

and band-limited white noise . In the MT8870 complex digital averaging algorithm provideexcellent immunity to voice, third tone and noissignals which prevail in a typical voice bandwidchannel.

The algorithm used in the MT8870 combines th

digital decoders with improvements resulting froyears of practical use within the telephonenvironment. The algorithm has evolved through combination of statistical calculations and empiric

"tweaks" to result in the realization of an extremereliable decoder.

Applications

The proven reliability of DTMF signalling has createa vast spectrum of possible applications. Unrecently, many of these applications were rendereineffective due to cost or size considerations. Nothat a complete DTMF receiver can be designed wimerely a single chip and a few external passivcomponents one can take full advantage of a high

developed signalling scheme as a small, coseffective signalling solution.

best features from two previous generations of Zarlin

7/27/2019 8870 App

8/23


A-52

Figure 7 - Modular Approach to DTMF Receiver Systems

SOURCE OFDTMF SIGNALS

TRANSMISSIONMEDIUM

INTERFACE DTMF

RECEIVER

CONTROL

LOGIC

FUNCTIONALINTERFACE

MT8870

The design of a DTMF receiving system cangenerally be broken down into three functionalblocks (Fig. 7). The first consideration is theinterface to the transmission medium. This may beas simple as a few passive components toadequately configure the MT8870s input stage or ascomplex as some form of demodulation, multiplexingor analog switching system. The second functionalblock is the DTMF receiver itself. This is where thereceiving systems parameters can be optimized forthe specific signal conditions delivered from the"front end" interface. The third, and perhaps mostwidely varying function, is the output control logic.This may be as simple as a 4 to 16 line decoder,controlling a specific function for each DTMF code,or as complex as a full blown computer handlingsystem protocols and adaptively varying the tonereceivers parameters to adjust for changing signalconditions. Several currently applied andconceptually designed applications are describedsubsequently but first lets consider the design of atypical input stage.

The input arrangement of the MT8870 provides adifferential input op amp as well as a bias source(VREF) which is used to bias the inputs at mid-rail.The output of this op amp is available to providefeedback for gain adjustment.

A typical single ended input configuration havingunity gain is shown in Figure 8.

For balanced line applications good common moderejection is offered by the differential configuration(Fig. 9). In both cases, the inputs are biased to 1/2VDD by VRef. Consider an input stage which willinterface to a 600 balanced line. To reject commonmode noise signals, a balanced differential amplifierinput provides the solution.

With the input configured for unity gain the MT8870will accept maximum signal levels of +1 dBm (into600). The lowest DTMF frequency that must bedetected is approximately 685Hz. Allowing 0.1dB of

Figure 8 - Single Ended Input Configuration

AV =Vo

Vi

Rf

R

S

S + 1/RC

Z() = R 1 + (1/RC)212

fc=1

2RC

Vi

Rf(3)

(2)

(1)

(4)

GS

IN-

IN+

VRef

+

-

Vo

MT8870

C R

Voltage Gain;

Input Impedance;

3dB Cutoff Frequency;

=-

7/27/2019 8870 App

9/23


A-53

attenuation at 685Hz, the required input timeconstant may be derived from;

Now, choosing R=220K gives a high inputimpedance (440K in the passband) and C=/R=6.9nF (use a standard value of 10 nF). Forunity gain in the passband we choose Rf=R. Ra andRb are biasing resistors. The choice of Ra is notcritical and could be set at, say... 68K. Bias resistorRa adds a zero to the non-inverting path through thedifferential amplifier but has no affect on the inverting

path. This zero can be exactly cancelled by theadded pole due to Rb if Rb is chosen as;

With appropriate input transient protection, thiscircuit will provide an excellent bridging interfaceacross a properly terminated telephone line for end-to-end or key system applications. Transientprotection may be achieved by splitting the inputresistors and inserting zener diodes to achievevoltage clamping (Fig. 10). This allows the transientenergy to be dissipated in the resistors and diodesand limits the maximum voltage that may appear atthe op-amp inputs.

It is important to consider the amount of shuntcapacitance introduced by the protection devices. Inthis case the parasitic capacitances of the zenerdiodes are in series which reduces their effect.Relatively large shunt capacitances will attenuate thehigh group frequencies causing the input signal totwist which degrades receiver performance.

M()dB=20 log10 +20 log10Rf

R

{()2 + 1}1/2

where M()dB is the amplifier gain in decibels

is the radian frequency

is the input time constant

Therefore -0.1=20 log10(2)685

{[(2)685]2 + 1}1/2

or = 1.52mS

Rb =RaRf

Ra+Rf.

Figure 9 - Differential Input Configuration

AV =Vo

Vi

Rf

R

S

S + 1/RC

Z() = 2R 1 + (1/RC)212

fc=1

2RC

Vi

Rf(3)

(2)

(1)

(4)

GS

IN-

IN+

VRef

Vo

MT8870

C R

Voltage Gain;

Input Impedance;

3dB Cutoff Frequency;

C R

=-

Rbselection; Rb=RaRf

Ra+ Rf

Ra Rb

-

+

Racan be chosen to be aconvenient value greaterthan 30K.

+

_

7/27/2019 8870 App

10/23


A-54

"Twist" is known as the difference in amplitudebetween the low and high group tones. It is specifiedin dB as:

Twist is usually caused by the frequency responsecharacteristic of the communication channel. Along atelephone line higher frequencies tend to roll offfaster than the lower ones so the line response isusually compensated for by applying pre-emphasis(negative twist) to the originating DTMF signal. Inextreme cases the receiver may requirecompensation. This could be realized with a filterarrangement utilizing the input op amp.

Any communication path that can pass the humanvoice spectrum is eligible for DTMF signalling.Therefore a variety of front-end interfaces may beapplicable in a given control system. Morecommonly used media are copper wire and RFchannels. An optical fibre could carry a light beammodulated by DTMF. Although this would incur alarge overhead in terms of bandwidth utilization,optical fibres do offer isolation from external electro-magnetic interference. For example, if control or

data signals must be sent near a high powertransmission line environment, strong electric andmagnetic fields could have a devastating effect onsignals transmitted over wires. DTMF over fibre-

optics could easily be employed as a highly reliablecommunications method in a harsh interferenceinfested environment.

In modern digital switching equipment the MT8870can easily be interfaced to a digital PCM line byusing a codec as an input interface (Fig. 11).Actually, all that is required for the interface is a PCM

decoder. In fact, the output filter that normally isassociated with PCM decoders is not required sincethe high group DTMF bandpass filter has an uppercutoff frequency low enough to meet the requiredroll-off of the PCM filter.

DTMF In Mobile Radio Applications

DTMF signalling plays an important role indistributed communications systems, such as multi-user mobile radio (Fig. 12). It is a "natural" in thetwo-way radio environment since it slips neatly into

the center of the voice spectrum, has excellent noiseimmunity and highly integrated methods ofimplementation are currently available. It is alsodirectly compatible with telephone signalling,simplifying automatic phone patch systems.

Several emergency medical service networkscurrently use DTMF signals to control radiorepeaters. Functions are, typically, mobileidentification, selection of appropriate repeater links,selection of repeater frequencies, reading ofrepeater status, and for completing automatic phone

patch links.

If available in a system of this type, audio from along distance communications link (microwave,

TWIST= 20log10VL

VH

where VL is the amplitude of the low frequency tone

and VHis the amplitude of the high frequency tone.

Figure 10 - MT8870 Front End Protection Circuit

TIP

RING

ZENERS ARE 15V 250mW

RESISTORS ARE 1% 1/4 W (unless otherwise stated)

0.01 f 110 K

1W

630 V

0.01 f

630 V 110 K

1W

110 K

110 K

52K

220K

MT8870

VRef

1

2

3

4

68K

7/27/2019 8870 App

11/23


A-55

Figure 11 - Interfacing The MT8870 To A Digital PABX Or Central Office

FROM DIGITALSWITCH

PCM DECODER

analogoutput

digitalinput

Vref

TO MICRO-PROCESSORBUS

MT8870 TONE RECEIVER

satellite, etc.) could be switched, via commands fromthe users DTMF keypad, into the local repeater.This would offer the mobile user a variety of paths for

communication without the assistance of a humanoperator.

Figure 12 - DTMF Controlled Radio Repeater

INTER-CONNECTING

LINK

COMUNICATIONS

LINKREPEATER

FMTRANSCEIVER

MT8870

RECEIVER

I.D.DECODE

HORNSWITCH

MT5089DTMFGENERATOR

DTMFKEYPAD

CALLINDICATOR

DTMF

INTER-CONNECTING

LINK

LOCALREPEATER

AUDIO SWITCHING(MT8804 CROSSPOINT

SWITCH)

MT8870DTMFRECEIVER

MT5089

PHONEPATCH

MICRO-PROCESSORCONTROL

USER MOBILESYSTEM

TO TELEPHONEEXCHANGE

DTMFGENERATOR

REPEATER CONTROL SYSTEMUSER MOBILE SYSTEM

Features include selective calling, intercommunity RF link and automatic phone patch.

7/27/2019 8870 App

12/23


A-56

A multi-channel repeater system serving a multitudeof user groups may be found to achieve its mosteffective performance in the "trunked" mode. In thiscase, one RF channel is reserved for systemsignalling. System operation could be achieved asfollows.

Each mobile plus the repeater system contain a

DTMF receiver, DTMF generator and appropriatecontrol logic. Mobiles are assigned individual DTMFI.D. codes and always monitor the signalling channelwhen idle. An originating mobile automatically sendsa DTMF sequence containing its own I.D. and theI.D. of the called party. This is recognized by therepeater control which retransmits the called partysI.D. The answering mobile returns a DTMFhandshake indicating to the repeater control that it isavailable to accept a call. At this time the repeatercontrol sends a DTMF command sequence to boththe originating and answering mobiles whichinstructs their logic circuits to switch to a specific,

available channel. If all channels are busy therepeater control could send DTMF sequences to putboth mobiles on "hold" and add their I.D.s to a"channel-request" queue. This arrangement would

allow users to access any available frequency andconverse privately instead of being restricted to oneassigned channel which is shared among severaluser groups.

As well as an individual I.D., each mobile belongingto a particular organization could also have acommon group I.D. This would allow dispatch

messages to be sent to all company mobilessimultaneously. Since mobiles would be underDTMF control, messages could be sent to anunattended vehicle and, at the users convenience,displayed on a readout .

Each radio link either established or attempted wouldresult in DTMF I.D. codes being sent to the repeatercontrol. These occurrences could easily be collectedby a computer for statistical analysis or billinginformation. Customers who have defaulted onrental payments could be denied access to the

system.

Simplified block diagrams of the control systems forboth the repeater and mobiles are shown in Figures13 and 14 respectively.

Figure 13 - Block Diagram of Control for "Trunked" Repeater System"

REPEATER RECEIVE

AUDIO PATHS

CH5 CH4 CH3 CH2 CH1

REPEATER TRANSMIT

AUDIO PATHS

CH5 CH4 CH3 CH2 CH1TX

RX

STATION

MONITORS

MT8804

4 x 8

CROSS-

POINT

SWITCH

MT8870

DTMF

RECEIVER

MT5089

DTMF

GENERA-

TOR

TEST/

PROGRAMMING

KEYPAD

AND DISPLAY

CONTROL LOGIC OR

SINGLE CHIP MICROCOMPUTER

TO TELEPHONE

EXCHANGE

PERIPHERAL PORT

HOST COMPUTER,

DATA LOGGER,

ETC

MT8804

4 x 8

CROSS-

POINT

SWITCHPHONE

PATCH

7/27/2019 8870 App

13/23


A-57

Figure 14 - Block Diagram of Mobile Radio Control System

MOBILE TRANSCEIVER

RECEIVER

FUNCTIONS

TRANSMITTER

FUNCTIONS

carrieroperated

squelch mute

receive

audio

transmit

enable

microphone

offhook

transmit

audio

MT8870

DTMF

RECEIVER

MT5089

DTMF

GENERATOR

CONTROL LOGIC OR

SINGLE CHIP MICROPROCESSOR

USER I.D. CODE

STRAPS

KEYPAD

AND DISPLAY

Distributed Control Systems

There are many other applications which also fallinto the distributed communications/control class.That is, several devices being controlled via acommon communications medium whether it be RF,copper wire or optical fibres, etc.

Consider, for example, an existing pair of wirescirculating throughout a plant. By connecting DTMFreceivers at strategic points along this path onecould conceivably control the whole plant from asingle DTMF transmitter (Fig. 15). Each DTMFreceiver would monitor the common line until itsspecific I.D. was received, at which time it wouldtransfer data to its functional control logic.

With some simple logic a circuit can be devised torecognize a sequence of programmed DTMF code.Figure 16 illustrates a method of detecting aDTMF code sequence of arbitrary length, N. Theobject is to compare N sequential 4-bit DTMF datawords to N preprogrammed 4-bit I.D. words.Programming the I.D. code is accomplished byapplying the desired logic levels to the inputs of N 4-bit bus buffers. This may be achieved with straps as

shown, dipswitches or thumbwheels. Pull-upresistors should be applied to the buffer inputs.Initially, after a RESET has occurred, Q0 of thepresettable shift register is set logically high, theremaining outputs are reset. This activates the firstbus buffer which applies its outputs to the Y inputs ofa 4-bit comparator.The LAST DIGIT latch is resetthe ERROR- flip-flop and VALID DIGIT latch areset. These three signals are ANDed indicating a nomatch condition. When a valid DTMF signal isreceived its data appears at the comparators Xinputs, a comparison occurs and the result appearsat the X=Y output. After 3.4 S (typical) Std risesindicating that the MT8870 output data is valid andstrobes X=Y into the VALID DIGIT latch. The shiftregister advances one position which enables thenext bus buffer. If the result of the comparison wastrue then the VALID DIGIT output is high. If aldigits of the sequence match then the high outputfrom the shift register wraps around from QN-1 toQ0, which strobes the LAST DIGIT latch high. Thisactivates the three input AND gate indicating amatch condition. If non-matching data is receivedany time during the detection sequence theERROR- flip-flop is reset which disables the ANDgate until a system RESET occurs. RESET maybe generated in a variety of ways depending on the

7/27/2019 8870 App

14/23


A-58

Figure 15 - Distributed Control System

DTMF

SIGNAL

SOURCE

I.D. DECODE

LOGIC

DRIVER VALVE

MT8870

DTMF

RECEIVER

I.D. DECODE

LOGIC

DRIVER VALVE

MT8870

DTMF

RECEIVER

COMPUTER

I.D. DECODE

LOGIC

DRIVER

MT8870

DTMF

RECEIVERSPRINKLER

ALARM

system design objective. If one DTMF code isreserved exclusively for the RESET function thenthe MT8870 outputs can be decoded directly. Thisrequires that the controller send a RESETcommand prior to sending an I.D. sequence.Alternatively a time-out timer, triggered by StD,

could serve to generate a system reset if a certaintime lapse occurs between received signals. Thismethod places time constraints on the system buteliminates the need to consume a DTMF commandfor the RESET function.

The concept of using a common transmissionmedium for control signalling applies to severalpossible situations. Plant process control, remotemeasurement control, selective intercom callsystems, institutional intercom systems, two wayradio control, pocket pagers and model car or boatremote control, just to mention a few.

Conversely, data could be collected from distributedsources. Implemented on a circulating wire or an RFchannel, as illustrated in Figure 17, information couldbe collected by a central unit which individually pollseach monitor to ask for data. Alternatively, thesystem could be interrupt driven (Fig.18). In thiscase each monitor, when ready to send data,generates an interrupt request by sending a DTMFI.D. sequence followed by a data stream. Interruptmasking or prioritizing could be achieved from thethe central control end by applying DC levels across

a wire pair or sending a pilot tone in an RF system.Remote data collection units would monitor thissignal to detect when a higher priority interupt isbeing handled or the communications channel isbusy.

Data Communication Using DTMF

There is a vast array of potential applications forDTMF signalling using the existing telephonenetwork. Considering that there are millions ofready-made data sets installed in convenientlocations (i.e. the Touch Tone telephone) remotecontrol and data entry may be performed by userswithout requiring them to carry around bulky datamodems.

Potential applications include:

home remote control

remote data entry from any Touch-Tone keypad

credit card verification and inquiry

salesman order entry

catalogue store (stock/price returned via voicesynthesis)

stock broker buy/sell/inquire -using stockexchange listing mnemonics

answering machine message retrieval

automatic switchboard extension forwarding

7/27/2019 8870 App

15/23


A-59

Figure 16 - N-Character Sequence Identifier

Q1Q2Q3Q4

X0X1X2X3

StD

X=Y

4-BITCOMPARATOR

Y3 Y2 Y1 Y0

I.D. DIGIT 0

STRAPS

I.D. DIGIT 1

STRAPS

I.D. DIGIT N-1

STRAPS

MT8870

D QD

LATCH

CK

S Q R Q

S

FLIP-FLOP

ERROR

VALID DIGIT

RESET MATCH

Q3 Q2 Q1Q0

Y3 Y2 Y1 Y0 OE

4-BITBUS BUFFER

Q3 Q2 Q1Q0

Y3 Y2 Y1 Y0 OE

4-BITBUS BUFFER

Q3 Q2 Q1Q0

Y3 Y2 Y1 Y0 OE

4-BITBUS BUFFER

VDD

LASTDIGIT

D QD

LATCH

CKR

RESETLOAD

Q0 Q1 ... ... ... QN-1

CK

Di

D0 D1 ... ...... DN-1

RESET

N-BIT PRESETTABLE SHIFT REGISTER

VDD

RESET GENERATED FROM A DEDICATED MT8870 OUTPUT BUS DECODE OR A TIME-OUT TIMER

This circut could be used to detect a valid I.D. number (address) or a "password".

A household DTMF remote control system with anoptional data port can boast a variety ofconveniences (Fig. 19). Remote ON/OFF controlmay be given to electric appliances such as a slowcooker, exterior lighting and garage heater. Anelectro-mechanical solenoid operated valve allowsremote control of a garden sprinkler. Video buffscould interface to their VCR remote control inputsand record T.V. shows with a few keystrokes of theirfriends telephone. This would enhance the functionof timers which are currently available on mostVCRs. Schedule changes or unexpectedbroadcasts could be captured from any remote

location featuring a Touch-Tone phone. Securitysystems could be controlled and a microphone couldbe switched in for remote audio monitoring.Interfacing a home computer to the data port makesan excellent family message center. At the remoteend messages are entered from a telephone keypadThe computer responds with voice messagesgenerated by a speech synthesizer. In the homemessages to be left are entered via the computerkeyboard. Messages to be read may be displayedon the computer monitor or played back throughthe speech synthesizer.

7/27/2019 8870 App

16/23


A-60

Figure 17 - DTMF Controlled Data Collection

Figure 18 - Interrupt Driven Data Collection System

MICROPROCESSORPOLLING

ALGORITHM

MT5089DTMF

GENERATORCONTROLTRANSCEIVER

CENTRAL CONTROL

MT8870DTMF

REMOTETRANSCEIVER

MT8870DTMF

RECEIVERAND I.D.DECODE

LOGIC

WATERLEVEL

MONITOR

MT5089DTMF

GENERATOR

RECEIVER

REMOTETRANSCEIVER

MT8870DTMF


LOGIC

SIESMIC

MONITOR

MT5089DTMF

GENERATOR

REMOTETRANSCEIVER

MT8870DTMF


LOGIC

WEATHER

STATION

MT5089DTMF

GENERATOR

Polling system for multiple location remote data collection.

REMOTE DATA

COLLECTION

MT8870

DTMFRECEIVER

DATALOGGER

MT5089DTMF

GENERATOR

LOGIC

INTERFACE

TEMPERATURETRANSDUCER

ALARMSENSOR

REMOTE MONITOR

PRIORITYSIGNAL

DETECTOR

MT8870

DTMF

RECEIVER

PRIORITY SIGNAL

INTERFACE

COMPUTER

MT5089

DTMF

GENERATOR

LOGIC

INTERFACE

PRESSURE

TRANSDUCER

ALARM

SENSOR

REMOTE MONITOR

PRIORITY

SIGNAL

DETECTOR

Remote monitors send data while the interconnecting pair of wires is clear of other interrupts.

7/27/2019 8870 App

17/23


A-6

Figure 19 - Home DTMF Remote Control System

Figure 20 - Using A Pushbutton Phone As A Data Terminal

TOUCH-TONEPHONE

OUTSIDEFLOOD

LIGHTSSLOW

COOKER

VIDEOCASSETTERECORDER

HOME DTMFCONTROLSYSTEM

YOUR

HOUSE

OPTIONALHOME COMPUTER

WITH VOICESYNTHESIZER

chili

1

ABC

2

DEF

3

GHI

4

JKL

5

MNO

6

PRS

7

TUV

8

WXY

9

*

OPER

0 #

ESC DEL ( ) BS \ /

! " . # $ % * + -

, ; : < = > ? @

BEL Q Z

SPACE

ACK=11CAN=58CR=19DC1=37

DC2=38DC3=39DC4=47DLE=29

EM=ENQ=EOT=ETB=

59090457

ETX=FF=FS=GS=

07186869

RETURN(a)

(b)

POS.4 POS.5 POS.6(?) (@) ()

POS.1 POS.2 POS.3

(W) (X) (Y)

NUMERAL(9)

TYPICAL KEY

KEYS "2" THROUGH "9" EACH REPRESENT THREE ALPHABETICCHARACTERS HENCE HAVE THREE INHERENT "POSITIONS"(POS.1, POS.2, AND POS.3) A PLASTIC OVERLAY CARD ADDSTHREE MORE POSITIONS (POS.4, POS.5, AND POS.6) TO KEYS"1" THROUGH "0". * AND # ARE RESERVED EXCLUSIVELY FORTHE SPACE AND RETURN FUNCTIONS.

a) Layout of a standard telephone keypad showing inherent character positions for coding purposes.b) Credit card size overlay expands each keys function by adding three more character positions.The * and # are reserved to send "SPACE" and "RETURN" as single key operations. Each other ASCII coderequires two keystrokes. To send a character simply push the button on or over which it appears, thenpush the numeral corresponding to its position. For example, to send a "T" push 8 followed by 1, tosend "%" push 5 followed by 6.

7/27/2019 8870 App

18/23


A-62

A scheme for coding ASCII characters using one andtwo digit DTMF signals is outlined in the appendix.Notice that on a telephone keypad keys 2 through 9are represented by three alpha-characters as well asa numeral. To send an alpha-character, using thisscheme, first press the key on which the characterappears then press the key corresponding to theposition in which the character appears on its key (1,

2 or 3 ). Numerals are sent by touching the desirednumber followed by a zero. The asterisk (*) andoctothorp (#) have been reserved for "space" and"return" respectively. A plastic overlay the size of acredit card expands the number of useable"positions" on each button (Fig. 20). This serves as aguide for sending other ASCII codes and fits snuginto a credit card wallet. ASCII control charactersthat are not commonly used could be listed at thebottom of the card. This user-friendly algorithm

eliminates the need to memorize conversion codesand allows significant functionality even without theoverlay reference.

A simple block diagram shows how this scheme maybe implemented for a home DTMF control system(Fig. 21). A ringing voltage detector signals themicroprocessor of an incoming call. The

microprocessor, after the prescribed number ofrings, closes the answer relay engaging the properterminating impedance. A two-to-four wire convertersplits bidirectional audio from the balancedtelephone line into separate single ended transmitand receive paths.

Receive audio is then switched to the DTMF receiverthrough the crosspoint switch. Upon receiving avalid DTMF signal, the microprocessor is alerted by

Figure 21 - Block Diagram of Home DTMF Remote Control System

FROM PHONEEXCHANGE

ANSWERRELAY

LINE TERMINATION2/4 WIRE CONVERTER

INAUDIO

OUT

OPTIONALFM TRANSMITTER

120V

MAINS

RINGDETECTOR

PASSWORDTHUMBWHEELS

OPTIONAL

MICROCOMPUTER

MT8804

CROSS-POINT

HANDSFREEINTERCOMSTATION

MT8870

DTMFRECEIVER

LOGIC ORMICROPROCESSOR

CONTROLSYSTEM

DATAPORT

OUTPUT

DRIVERS

REMOTEFM/DTMF

RECEIVERAND

CONTROL

OUTPUTDRIVERS

TO REMOTECONTROLLED

DEVICES

TO NEARBYCONTROLLED

DEVICES

SWITCH

An FM transmitter could be used to couple control signals for distribution over existing power lines. Thiswould eliminate the need for installing wires between the DTMF control unit and remote controlleddevices.

7/27/2019 8870 App

19/23


A-63

the rising edge of StD. The microprocessor thenchecks for a valid password sequence and decodessubsequent commands. A command can be enteredto put the system into remote-control mode. In thiscase the crosspoint switch is configured to routeDTMF signals into the FM-over-mains transmitter aswell as the system tone receiver. Forwarding ofcontrol signals is accomplished by applying an FM

carrier to the power line. This eliminates the need tostring control wires haphazardly about the house.The appropriate device is selected by its uniqueDTMF I.D. code. The microcomputer keeps track ofall device locations and their I.D. codes since it mustdecide when to supply function outputs to thenearby devices and when to let the remotereceivers handle the data. Subsequent data istransmitted to a selected device until a resetcommand is entered.

Upon receiving any DTMF signal, answer back tonesare returned by the microprocessor to acknowledge

valid or invalid operations and to indicate the state ofan interrogated device. For example, a low to hightone transition could indicate that a particular deviceis on, a high to low transition indicating the off state.A command could be entered to put the system in anexternal mode which would allow communicationsthrough the data port. A host computer could beconnected to this port to broaden the scope of thesystem.

The resident microprocessor unit contains thesoftware and hardware to control ringing verification,

password and command decoding, answer back tonegeneration, audio routing, output function latchesand an optional data port. Output drivers buffer thelatches and switch relays or SCRs to controperipheral devices.

An infinite variety of devices could be controlled bysuch a system, the spectrum of which is limited only

by the ability to provide appropriate interfacing. Thissystem could also be the heart of a DTMF intercomsystem allowing intercommunication, "phone-patching", and remote control from varied householdlocations. This type of system concept is, of courseanything but limited to home use. Many applicationscan provide conveniences to consumerssalespeople and executives.

For example, a merchant could verify credit cardaccounts quickly utilizing only a telephone keypad fordata entry (Fig. 22). Each credit card company could

reserve one or more telephone lines to provide thisfunction, reducing the human effort required. Thereceiving end system would be required to answerthe call, provide a short answer back tone ormessage, receive and decode the credit cardaccount number, verify it, verify the owners nameand give a go/no-go authorization. This return datacould easily be provided with the aid of a voicesynthesizer. An auto-dialler containing appropriatephone numbers could be installed at the merchantend as an added time saver.

Figure 22 DTMF Data Communications For An Auto Verification Line

CASHIERS

PHONE

OPTIONALAUTO

DIALER

AUTO

ANSWER/

LINE

TERMINATION

MT8870

DTMF

RECEIVER

CREDIT CARD

ACCOUNTING

COMPUTER

VERIFICATION/

AUTHORIZATIONALGORITHM

SPEECH

SYTHESIZER

CREDIT CARD COMPANY - AUTO VERIFICATION LINE

7/27/2019 8870 App

20/23


A-64

With a similar arrangement, a travelling salesmancould access price, delivery and customer status,enter or delete merchandise orders and retrievemessages all from the comfort of the customersoffice (Fig. 23a). A department store could provideshop-by-phone service to its customers usingtelephone keypad data entry (Fig. 23b). Brokeragefirms, utilizing the stock exchange mnemonic listings

could provide trading price information and buy/sellservice via telephone keypad entry. A voicesynthesizer could provide opening and currenttrading price, volume of transactions and otherpertinent data. A telephone answering systemmanufacturer could apply this technique, allowingusers to access and change outgoing and incomingmessages from a Touch-Tone phone.

A PBX manufacturer could offer a feature thatrelieves the switchboard attendant from unneccesaryinteraction. A call could be answered automaticallyand a recording may reply Thank you for calling

XYZ. Please dial the extension you wish to contactor zero for the switchboard. If the caller knows thecalled partys extension in advance it is notneccesary to wait for the switchboard attendant to

forward the call. The attendant could be notified tointervene if there is no action by the caller say, tenseconds after the recording ends. This provides asimilar function to a Direct Inward Dialling (DID)trunk but without the additional overhead incurredwith renting a block of phone numbers as in the DIDcase.

Now that a DTMF receiver is so easy andinexpensive to implement there are many simplededicated uses that become attractive. A usefulhome and office application for DTMF receivers is ina self-contained telephone-line-powered toll callrestrictor similar to the block diagram in Fig. 2a. Thiscould be installed in an individual telephone or at theincoming main termination depending on whichphone or phones are to be restricted. Whiledisallowing visitors from making unauthorized longdistance calls, the owner may still desire access totoll dialling. This could be provided by adding a logiccircuit that disables the toll restrictor upon receiving

a predetermined sequence of DTMF characters (Fig.16). In this case, the user must enter his passwordbefore dialling a long distance number.

Figure 23 - Two Applications Of DTMF Data Communications

OUTSIDE SALES

PERSON ATCUSTOMERS

TELEPHONE

CONSUMER AT

HOME PHONE

SALES WAREHOUSE/OFFICE

CATALOGUE SHOPPING WAREHOUSE

AUTO

ANSWER/

LINETERMINATION

MT8870

DTMFRECEIVER

ORDER ENTRY

COMPUTER

STOCK/PRICE/DELIVERY

ALGORITHM

SPEECH

SYNTHESIZER

OPTIONAL

AUTO

DIALER

AUTO

ANSWER/

LINE

TERMINATION

MT8870

DTMF

RECEIVER

ORDER ENTRY

COMPUTER

STOCK/PRICE/

DELIVERY

ALGORITHM

SPEECH

SYNTHESIZER

(a)

(b)

7/27/2019 8870 App

21/23


A-65

Conclusion

The applications for DTMF signalling are tremendousand due to innovative technological advances its useis increasingly widespread. DTMF offers highlyreliable, cost effective signalling solutions whichrequire no development effort on the users part.The advent of single chip receivers has allowedmany products that were previously not cost-effective to be manufactured in production quantities.

DTMF signalling was originally designed fortelephony signalling over voice quality telephonelines. This signalling technique has been applied toa multitude of control and data communicationssystems. All that is required is a voice qualitycommunication channel with appropriateinterfacing. The applications are limited only byones imagination.

7/27/2019 8870 App

22/23


A-66

Appendix

ASCII TO DTMF CONVERSION

Partial ASCII coding and conversion to 2 sequential DTMF signals

ASCII HEX DTMF ASCII HEX DTMF ASCII HEX DTMF

ACK 06 11 ! 21 44 A 41 21BEL 07 01 " 22 45 B 42 22BS 08 34 # 23 54 C 43 23

CAN 18 58 $ 24 55 D 44 31CR 0D 19 % 25 56 E 45 32

DC1 11 37 & 26 79 F 46 33DC2 12 38 27 16 G 47 41DC3 13 39 ( 28 25 H 48 42DC4 14 47 ) 29 26 I 49 43DEL 7F 24 * 2A 64 J 4A 51DLE 10 29 + 2B 65 K 4B 52EM 19 59 2C 74 L 4C 53

ENQ 05 09 - 2D 66 M 4D 61EOT 04 08 . 2E 46 N 4E 62ESC 1B 14 / 2F 36 O 4F 63

ETB 17 57 0 30 00 P 50 71ETX 03 07 1 31 10 Q 51 02FF 0C 18 2 32 20 R 52 72FS 1C 68 3 33 30 S 53 73GS 1D 69 4 34 40 T 54 81HT 09 12 5 35 50 U 55 82LF 0A 13 6 36 60 V 56 83

NAK 15 48 7 37 70 W 57 91NUL 00 04 8 38 80 X 58 92RS 1E 77 9 39 90 Y 59 93S0 0E 27 : 3A 76 Z 5A 03S1 0F 28 ; 3B 75 [ 5B 87

SOH 01 05 < 3C 84 \ 5C 35SP 20 * = 3D 85 ] 5D 88

STX 02 06 > 3E 86 ^ 5E 96SUB 1A 67 ? 3F 94 _ 5F 89SYN 16 49 @ 40 95 60 15US 1F 78 DEL 7F 24VT 0B 17

7/27/2019 8870 App

23/23

www.zarlink.com

Information relating to products and services furnished herein by Zarlink Semiconductor Inc. trading as Zarlink Semiconductor or its subsidiaries (collectively Zarlink)is believed to be reliable. However, Zarlink assumes no liability for errors that may appear in this publication, or for liability otherwise arising from the application oruse 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 fromsuch application or use. Neither the supply of such information or purchase of product or service conveys any license, either express or implied, under patents orother intellectual property rights owned by Zarlink or licensed from third parties by Zarlink, whatsoever. Purchasers of products are also hereby notified that the useof product in certain ways or in combination with Zarlink, or non-Zarlink furnished goods or services may infringe patents or other intellectual property rights ownedby Zarlink.

This publication is issued to provide information only and (unless agreed by Zarlink in writing) may not be used, applied or reproduced for any purpose nor form partof any order or contract nor to be regarded as a representation relating to the products or services concerned. The products, their specifications, services and otherinformation appearing in this publication are subject to change by Zarlink 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 guaranteethat such methods of use will be satisfactory in a specific piece of equipment. It is the user

s responsibility to fully determine the performance and suitability of anyequipment using such information and to ensure that any publication or data used is up to date and has not been superseded. Manufacturing does not necessarilyinclude testing of all functions or parameters. These products are not suitable for use in any medical products whose failure to perform may result in significant injuryor death to the user. All products and materials are sold and services provided subject to Zarlink

s conditions of sale which are available on request.

Purchase of Zarlink s I

2

C components conveys a licence under the Philips I

2

C Patent rights to use these components in and I

2

C System, providedthat the system conforms to the I

2

C Standard Specification as defined by Philips.

Zarlink and the Zarlink Semiconductor logo are trademarks of Zarlink Semiconductor Inc.

Copyright 2001, Zarlink Semiconductor Inc. All Rights Reserved.

TECHNICAL DOCUMENTATION - NOT FOR RESALE

For more information about all Zarlink products

visit our Web Site at

8870 app

Documents