MITEL MT8843AS, MT8843AE Datasheet



CMOS

MT8843

Calling Number Identif ica tion Circuit 2

Preliminary Information

Features

• Compatible with B riti s h Telecom (BT ) S IN 22 7 & SIN242, Cable Television Association (CTA) TW/P&E/312, and Bellcore TR-NWT-000030 & SR-TSV-002476

• Ring and lin e reve rsal de tectio n

• Bellcore "CP E Al erting Si gnal (C AS) " and B T "Idle State Tone Alert Signal" d etect ion

• 1200 baud BELL 202 and CCITT V.23 Frequen cy Shift K eying (FSK) demo dulati on

• High input sensi tivit y

• Dual mode 3 -wire da ta in terface

• Low power CMO S wi th powerd ow n mode

• Input gain ad ju stable am pli fier

• Carrier dete ct sta tus ou tput

• Uses 3.58 MHz crystal or ceramic resonator

Applications

• BT Calling L ine Iden tity P rese ntation (CLIP ), CT A CLIP, and Bellcore Calling Identity Delivery (CID) systems

• Feature ph ones, includ ing Ana log Di splay Services Inte rface (ADSI) pho ne s

• Phone se t adjunc t box es

• FAX and answering ma chine s

• Databas e query an d Co mpu ter Telephony Integration (CTI) systems

ISSUE 1 February 1995

Ordering Information

MT8843AE 24 Pin Plastic DIP MT8843AS 24 Pin SOIC

-40 °C to +85 °C

Description

The MT8843 Calling Number Identification Circuit 2 (CNIC2) is a low power CMOS integrated circuit intended for receiving physical layer signals transmitted according to BT (British Telecom) SIN227 & SIN242, CTA (Cable TV Association) TW/ P&E/312 and Bellcore TR-NWT-000030 & SR-TSV002476 specifications.

The CNIC2 provides all the features and functions offered by Mitel’s MT8841 (CNIC), including 1200 baud BELL 202 and CCITT V.23 FSK demodulation. The 3-wire serial FSK interface provided by CNIC has been enhanced to operate in two modes. The first mode is the CNIC compatible mode whereby data transfer is initiated by the device. The new, second mode allows a microcontroller to extract 8-bit data words from the device. Furthermore, CNIC2 offers Idle State Tone Alert Signal and line reversal detection capability for BT’s CLIP, ring burst detection for CTA’s CLIP, and ring detection for Bellcore’s CID.

IN+

IN-

VRef

CAP

PWDN

Generator

Oscillator

OSCin OSCout

Anti-alias

To internal

cct.

Bias

To internal cct.

Filter

FSK Bandpass

Filter

Alert Signal High

Tone Filter

Alert Signal Low

Tone Filter

TRIGRCTRIGin

Demodulator

TRIGout

Figure 1 - Functional Block Diagram

FSK

Carrier

Detector

Tone Detection Algorithm

FSKen

MODE

Data Timing

Recovery

Interrupt

Generator

Guard Time

DCLK DATA DR

INT

StD St/GT

ESt VDD

VSS

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Preliminary Information MT8843

Pin Description

Pin # Na me Description

18 DR 3-wire FSK Interface Data Ready (CMOS Output). Active low.This output goes low after

the last DCLK pulse of eac h word. Th is ide ntifies the data (8 -bit word ) bound ary on the serial output strea m. Typically, DR converte r into a m icroc ontrol ler.

is used to latc h 8-bi t words from th e serial -to-p arallel

19 CD

Carrier Dete ct (C M OS O u tpu t). Active low. A logic low indicates the presence of in-band signal a t the ou tput of t he FS K band pass filter.

20 INT

Interrupt (Open Drain Output). Active low. It is active when TRIGout or DR is low, or StD is high. This output stays low until all three signals have become inactive.

21 StD Dual Tone Alert Signal Delayed Steering Output. When high, it indicates that a guard

time qua lifie d alert sig na l has bee n det ected .

22 ESt Dual Tone Alert Sign al Ea rly Ste ering Outp ut. Al ert signa l det ection ou tput. Use d in

conjuncti on wit h St/G T and ex terna l circui try to impleme nt de tect and non -det ect gua rd times.

23 St/GT Dual Tone Alert Signal Steering Input/Guard Time (Analog Input/CMOS Output).

A voltage greater than V pair and update the output latch. A voltage less than V

detected at St ca u s es t he device to re gi s t er the detected to ne

TGt

frees the d evi ce to acc ept a

TGt

new tone pa ir. The GT outpu t act s to re set th e ex ternal steerin g t im e-constant; its stat e is a functio n of ESt and t he voltag e o n St.

24 V

Functional Overview

Positive Power Supply.

alert signal as well as to receive and demodulate the incoming CCITT V.23 FSK signals.

The MT8843 Calling Number Identification Circuit 2 (CNIC2) is a device compatible with BT, CTA and Bellcore specifications. As shown in Figure 1, CNIC2 provides an FSK demodulator as well as a 3-wire serial interface similar to that of it’s predecessor, the MT8841 (CNIC). The 3-wire interface has been enhanced to provide two modes of operation - a mode whereby data transfer is initiated by the device and a mode whereby data transfer is initiated by an external microcontrolle r.

TW/P&E/312 proposes an alternate CDS TE interface available for use in the CTA network. According to TW/P&E/312, data is transmitted after a single burst of ringing rather than before the first ringing cycle (as specified in SIN227). The Idle State Tone Alert Signal is not required as it is replaced with a single ring burst. CNIC2 has the capability to detect the ring burst. It is also able to demodulate either Bell-202 or CCITT V.23 FSK data following the ring burst, as specified by the CTA.

In addition to supporting all the features and functions offered by MT8841, CNIC2 provides line reversal detection, ring detection and dual tone alert signal detection capability. These new functions eliminate some external application circuitry previously required with the MT8841 (CNIC).

SIN227 and SIN242 specify the signalling mechanism between a network and a Terminal Equipment (TE) providing Caller Display Service (CDS). CDS provides Calling Line Identity Presentation (CLIP), that is, delivery of the identity of the caller when a telephone call arrives, before the start of ringing (in the Idle State).

An incoming CDS call is indicated by a polarity reversal on the A and B wires (line reversal), followed by an Idle State Tone Alert Signal. CNIC2 has the capability to detect both the reversal and

TR-NWT-000030 specifies generic requirements for transmitting asynchronous voiceband data to Customer Premises Equipment (CPE). SR-TSV002476 describes the same requirements from the CPE’s perspective. The data transmission technique specified in both documents is applicable in a variety of services like Calling Number Delivery (CND), Calling Name Delivery (CNAM) and Calling Identity Delivery on Call Waiting (CIDCW) - services promoted by Bellcore.

In CND/CNAM service, information about a calling party is embedded in the silent interval between the first and second ring. CNIC2 detects the first ring and can then be setup to receive and demodulate the incoming Bell-202 FSK data. The device will output the demodulated data onto a 3-wire serial interface.

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Preliminary Information MT8843

The diode bridge shown in Figure 3 half wave rectifies a single ended ring signal. Full wave rectification is achieved if the ringing is balanced. A fraction of the ring voltage is applied to the TRIGin input. When the voltage at TRIGin is above the Schmitt trigger high going threshold VT+, TRIGRC is pulled low as C3 discharges. TRIGout

stay s low as

long as the C3 voltage stays below the minimum

T+

In a CPE designed for CND/CNAM, TRIGout

high to low transition may be used to interrupt or wake up the microcontroller. The controller can thus be put into sle ep mode to c onserve po w er.

Dual Tone Alert Signal Detect ion

According to SIN227 the Idle State Tone Alert Signal allows more reliable detection of Caller Display Service signals. The Idle State Tone Alert Signal follows the line reversal and a silence period. The characteristics of the BT’s idle state alerting tone is shown in Table 1.

Item BT Bellcore

Low tone

2130Hz ±1.1% 2130Hz± 0.5%

frequency High tone

2750Hz±1.1% 2750Hz±0.5%

frequency Received

signal level

-2dBV to -40dBV

per tone on-hook

(0.22dBm

-14dBm to -32dBm

per tone off-hook

-37.78dBm)

Signal reject level

Signal level

-46dBV

-45dBm

(-43.78dBm)

up to 7dB up to 6dB differential (twist)

Unwanted signals

<= -20dB

(300-3400Hz) Duration 88ms to 110ms Speech

No Yes

<= -7dBm ASL

near end speech

75ms to 85ms

present

Table 1. Dual Tone Alert Signal Ch arac teri stics

a. The o ff-ho ok s ig na l le ve l is -15dB m to - 34 dB m pe r to ne to b e

specifie d in the BT CIDC W s pe c ifi ca ti on in th e future.

b. The si gn al po w er i s e xp res s ed in dBm r ef ere nc ed to 600 o hm

at the CPE A/B (tip/r ing) int erf ace.

c. ASL = ac ti ve s pe ec h le ve l ex pr e s sed in dBm referenc ed to

600 oh m at th e C P E ti p/ r in g i nte rf a c e. The l ev el is m easured according to method B of Recommendation P.56 "Objective Measurem e nt of Active Spee ch Lev el " publ is he d in th e CCI TT Blue Book, volume V "Telephone Transmission Quality" 1989. EPL (Equivalent Pe ak L evel ) = ASL+11.7dB

d. SIN2 27 s ug ge s ts tha t the recogn ition tim e sh ou ld be not le s s

than 20m s if both ton es a re detect ed .

Bellcore specifies a similar dual tone alert signal called CPE Alerting Signal (CAS) for use in off-hook data transmission. Bellcore states that the CPE should be able to detect, in the presence of voice, the CPE A lerti n g Sig nal.

The dual tone alert signal is separated into the high and low tones with two bandpass filters. A detection algorithm examines the two filter outputs to determine the presence of a dual tone alert signal. The ESt pin goes high when both tones are present. Detect and non-detect guard times can be implemented with external RC components. The guard times improve detection performance by rejecting signals of insufficient duration and masking momentary detection dropout. StD is the guard time qualified detector output.

• Dual Tone Detection Guard Time

When the dual tone alert signal is detected by the CNIC2, ESt is pulled high. When the alerting signal ceases to be detected, ESt goes low.

Figure 4 shows the relationship between the St/GT, ESt and StD pins. It also shows the operation of a guard time circuit. The guard time circuit improves detection performance by rejecting detections of insufficient duration and by allowing momentary ESt dropouts once the duration criterion has been met.

The total recognition time is t t

is the tone present guard time and tDP is the tone

= tGP + tDP, where

REC

present detect time (refer to timing between ESt, St/ GT and StD in Figures 15 and 18).

The total tone absent time is t t

is the tone absent guard time and tDA is the tone

= tGA + tDA, where

ABS

absent detect time (refer to timing between ESt, St/ GT and StD in Figures 15 and 18).

Bellcore states that it is desirable for an off-hook capable CPE to have a CAS detector on/off switch. The switch was conceived so that a subscriber who disconnects a service that relies on CAS detection (e.g., CIDCW ), but retain s the CPE, can tu rn off the detector and not be bothered by false detection.

SW1 in Figure 4 performs the above function. In the B position, the comparator input, hence StD, is always low. The CAS detector will not be enabled and its output will not cause interrupts (except for the system power up condition described in section “Interrupt” on page 28’).

BT states that the idle state tone alert signal recognition time should be no less than 20ms when

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