5-21

Features

Compatible with British Telecom (BT) SIN227 &
SIN242, Cable Television Association (CTA)
TW/P&E/312, and Bellcore TR-NWT-000030 &
SR-TSV-002476

Ring and line reversal detection

Bellcore "CPE Alerting Signal (CAS)" and BT
"Idle State Tone Alert Signal" detection

1200 baud BELL 202 and CCITT V.23
Frequency Shift Keying (FSK) demodulation

High input sensitivity

Dual mode 3-wire data interface

Low power CMOS with powerdown mode

Input gain adjustable amplifier

Carrier detect status output

Uses 3.58 MHz crystal or ceramic resonator

Applications

BT Calling Line Identity Presentation (CLIP),
CTA CLIP, and Bellcore Calling Identity Delivery
(CID) systems

Feature phones, including Analog Display
Services Interface (ADSI) phones

Phone set adjunct boxes

FAX and answering machines

Database query and Computer Telephony
Integration (CTI) systems

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-TSV-
002476 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.

Figure 1 - Functional Block Diagram

Anti-alias

Filter

FSK Bandpass

Filter

FSK

Demodulator

Data Timing

Recovery

Carrier

Detector

Alert Signal High

Tone Filter

Alert Signal Low

Tone Filter

Tone

Detection
Algorithm

Bias

Generator

Oscillator

Guard
Time

StD

St/GT

ESt

TRIGout

TRIGRC

TRIGin

DATA
DR

DCLK

MODE

FSKen

CAP

OSCin OSCout

IN+

IN-

VRef

INT

PWDN

VDD
VSS

To internal

To internal cct.

cct.

Interrupt

Generator

ISSUE 1

February 1995

Ordering Information

MT8843AE

24 Pin Plastic DIP

MT8843AS

24 Pin SOIC

-40 °C to +85 °C

MT8843

Calling Number Identification Circuit 2

CMOS

Preliminary Information

Preliminary Information

MT8843

5-23

3-wire FSK Interface Data Ready (CMOS Output). Active low.This output goes low after
the last DCLK pulse of each word. This identifies the data (8-bit word) boundary on the
serial output stream. Typically, DR is used to latch 8-bit words from the serial-to-parallel
converter into a microcontroller.

Carrier Detect (CMOS Output). Active low. A logic low indicates the presence of in-band
signal at the output of the FSK bandpass filter.

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.

StD

Dual Tone Alert Signal Delayed Steering Output. When high, it indicates that a guard
time qualified alert signal has been detected.

ESt

Dual Tone Alert Signal Early Steering Output. Alert signal detection output. Used in
conjunction with St/GT and external circuitry to implement detect and non-detect guard
times.

St/GT

Dual Tone Alert Signal Steering Input/Guard Time (Analog Input/CMOS Output).
A voltage greater than V

TGt

detected at St causes the device to register the detected tone

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

TGt

frees the device to accept a

new tone pair. The GT output acts to reset the external steering time-constant; its state is
a function of ESt and the voltage on St.

Positive Power Supply.

Pin Description

Pin #

Name

Description

Functional Overview

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 microcontroller.

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

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

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.

TR-NWT-000030 specifies generic requirements for
transmitting asynchronous voiceband data to
Customer Premises Equipment (CPE). SR-TSV-
002476 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.

Preliminary Information

MT8843

5-25

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 V

T+

, TRIGRC is

pulled low as C3 discharges. TRIGout stays low as
long as the C3 voltage stays below the minimum
V

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 sleep mode to conserve power.

Dual Tone Alert Signal Detection

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.

a. The off-hook signal level is -15dBm to -34dBm per tone to be

specified in the BT CIDCW specification in the future.

b. The signal power is expressed in dBm referenced to 600 ohm

at the CPE A/B (tip/ring) interface.

c. ASL = active speech level expressed in dBm referenced to

600 ohm at the CPE tip/ring interface. The level is measured
according to method B of Recommendation P.56 "Objective
Measurement of Active Speech Level" published in the CCITT
Blue Book, volume V "Telephone Transmission Quality" 1989.
EPL (Equivalent Peak Level) = ASL+11.7dB

d. SIN227 suggests that the recognition time should be not less

than 20ms if both tones are detected.

Item

Bellcore

Low tone
frequency

2130Hz ±1.1%

2130Hz± 0.5%

High tone
frequency

2750Hz±1.1%

2750Hz±0.5%

Received
signal level

-2dBV to -40dBV

per tone on-hook

(0.22dBm

-37.78dBm)

-14dBm to -32dBm

per tone off-hook

Signal reject
level

-46dBV

(-43.78dBm)

-45dBm

Signal level
differential
(twist)

up to 7dB

up to 6dB

Unwanted
signals

<= -20dB

(300-3400Hz)

<= -7dBm ASL

near end speech

Duration

88ms to 110ms

75ms to 85ms

Speech
present

Yes

Table 1. Dual Tone Alert Signal Characteristics

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 Alerting Signal.

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

REC

= t

+ t

, where

is the tone present guard time and t

is the tone

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

The total tone absent time is t

ABS

= t

+ t

, where

is the tone absent guard time and t

is the tone

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 retains the CPE, can turn 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

Preliminary Information

MT8843

5-27

Note that signals such as dual tone alert signal,
speech and DTMF tones lie in the same frequency
band as FSK. They will, therefore, be demodulated
and as a result, false data will be generated. To avoid
demodulation of false data, an FSKen pin is provided
so that the FSK demodulator may be disabled when
FSK signal is not expected.

The FSK characteristics described in Table 2 have
been specified in BT and Bellcore specifications. The
BT signal frequencies correspond to CCITT V.23. The
Bellcore frequencies correspond to Bell 202. CTA
requires that the TE be able to receive both CCITT
V.23 and Bell 202, as specified in the BT and Bellcore
specifications. CNIC2 is compatible with both formats
with no external intervention.

CNIC2 will meet these characteristics with its input
op-amp at unity gain.

a. The signal power is expressed in dBm referenced to 600 ohm

at the CPE tip/ring (A/B) interface.

b. TR-NWT-000030, Bulletin No. 1
c. The frequency range is specified in TR-NWT-000030.
d. Up to 20 marks may be inserted in specific places in a single

or multiple data message.

Item

Bellcore

Mark
frequency
(logic 1)

1300Hz

± 1.5%

1200Hz

± 1%

Space
frequency
(logic 0)

2100Hz

± 1.5%

2200Hz

± 1%

Received
signal level -
mark

-8dBV to

-40dBV

(-5.78dBm to

-37.78dBm)

-12dBm

-32dBm

Received
signal level -
space

-8dBV to

-40dBV

-12dBm to

-36dBm

Signal level
differential
(twist)

up to 6dB

up to 10dB

Unwanted
signals

<= -20dB

(300-3400Hz)

<= -25dB

(200-3200Hz)

Transmission
rate

1200 baud

± 1%

1200 baud

± 1%

Word format

1 start bit (logic

0), 8 bit word

(LSB first), 1 to

10 stop bits

(logic 1)

1 start bit (logic

0), 8 bit word

(LSB first),

1 stop bit
(logic 1)

Table 2. FSK Characteristics

3-wire User Interface

The MT8843 provides a powerful dual mode 3-wire
interface so that the 8-bit data words in the
demodulated FSK bit stream can be extracted
without the need either for an external UART
(Universal Asynchronous Receiver Transmitter) or
for the TE/CPE's microcontroller to perform the
UART function in software (asynchronous serial data
reception). The interface is specifically designed for
the 1200 baud rate and is comprised of the DATA,
DCLK (data clock) and DR (data ready) pins. Two
modes (modes 0 and 1) are selectable via control of
the device's MODE pin: in mode 0, data transfer is
initiated by the CNIC2; in mode 1, data transfer is
initiated by the external microcontroller.

Mode 0

This mode is selected when the MODE pin is low. It
is the CNIC (MT8841) compatible mode where data
transfer is initiated by the device.

In this mode, CNIC2 receives the FSK signal,
demodulates it, and outputs the extracted data to the
DATA pin (refer to Figure 12). For each received stop
and start bit sequence, the CNIC2 outputs a fixed
frequency clock string of 8 pulses at the DCLK pin.
Each clock rising edge occurs in the centre of each
DATA bit cell. DCLK is not generated for the stop and
start bits. Consequently, DCLK will clock only valid
data into a peripheral device such as a serial to
parallel shift register or a micro-controller. CNIC2
also outputs an end of word pulse (data ready) at the
DR pin. The data ready signal indicates the reception
of every 10-bit word sent from the network to the TE/
CPE. This DR signal is typically used to interrupt a
micro-controller.

Mode 1

This mode is selected when the MODE pin is high. In
this mode, the microcontroller supplies read pulses
(DCLK) to shift the 8-bit data words out of the
MT8843, onto the DATA pin. CNIC2 asserts DR to
denote the word boundary and indicate to the
microprocessor that a new word has become
available (refer to Figure 14).

Internally, the MT8843's demodulated data bits are
sampled and stored. After the 8th bit, the word is
parallel loaded into an 8 bit shift register and DR
goes low. The shift register's contents are shifted out
to the DATA pin on DCLK's rising edge in the order
they were received.

If DCLK begins while DR is low, DR will return to high
upon the first DCLK. This feature allows the
associated interrupt (see section on "Interrupt") to be

Preliminary Information

MT8843

5-29

The crystal specification is as follows:

Frequency:

3.579545 MHz

Frequency tolerance:

±0.1%(-40°C+85°C)

Resonance mode

Parallel

Load capacitance:

18 pF

Maximum series resistance

: 150 ohms

Maximum drive level (mW):

2 mW

e.g., CTS MP036S

Any number of MT8843 devices can be connected
as shown in Figure 8 such that only one crystal is
required. The connection between OSC2 and OSC1
can be D.C. coupled as shown, or the OSC1 inputs
on all devices can be driven from a CMOS buffer (dc
coupled) with the OSC2 outputs left unconnected.

VRef and CAP Inputs

Ref

is the output of a low impedance voltage source

equal to V

DD/2

and is used to bias the input op-amp.

A 0.1µF capacitor is required between CAP and V

to suppress noise on V

Ref.

Applications

The circuit shown in Figure 9 illustrates the use of the
MT8843 (CNIC2) device in a typical CID or CLIP sys-
tem. Network protection will differ depending on the
market for which the product is designed.

Notes:

CNIC2 has not been fully characterized for talkoff
and talkdown performance as specified in SR-TSV-
002476.

For CIDCW, speech immunity improves if near end
audio is cancelled from the incoming signal. One
possible implementation is to connect the signal
input to the 2 wire side when the CPE is on-hook and
the 4 wire side when the CPE is off-hook.

Figure 9 - Application Circuit

IN+

IN-

Ref

TRIGin

TRIGRC

TRIGout

MODE

OSCin

OSCout

St/GT

ESt

StD

INT

DATA

DCLK

FSKen

PWDN

CNIC2

CAP

(FSK Interface Mode 0 selected)

+5V

= To microcontroller

= From microcontroller

1µ

TIP / A

RING / B

Notes

MT8843

+5V

430K

34K

464K

500K

200K

300K

0.1µF

0.01µF

µF

420K

TISP4180,

TPA150A12 or
TPB150B12

TISP5180,

+5V

100K

For BT network

protection:

Note: For CTA applications where there is a requirement to determine
the ring burst duration, the value of R and C may have to be optimized.

Preliminary Information

MT8843

5-31

DC Electrical Characteristics are over recommended operating conditions unless otherwise stated.
Note 1 - Magnitude measurement, ignore signs.

TRIGout,

DCLK,

DATA, DR,

CD, StD,

ESt , St/GT

TRIGRC,

INT

Output Low Sinking Current

2.5

=0.1*V

IN+, IN-,

TRIGin

Input Current

Iin1

or V

See Note 1

PWDN,

DCLK,

MODE,

FSKen

Iin2

or V

See Note 1

TRIGRC

Output High-Impedance
Current

Ioz1

out

or V

See Note 1

INT

Ioz2

St/GT

Ioz3

Ref

Output Voltage

Ref

0.5V

0.05

0.5V

0.05

No Load

St/GT

Comparator Threshold
Voltage

TGt

0.5V

0.05

0.5V

0.05

DC Electrical Characteristics

Characteristics

Sym

Min

Max

Units

Test Conditions

Preliminary Information

MT8843

5-33

Electrical characteristics are over recommended operating conditions, unless otherwise stated.
Typical figures are at 25°C and are for design aid only: not guaranteed and not subject to production testing.

*Notes
1. Both mark and space have the same amplitude.
2. Band limited random noise (200-3400Hz). Present when FSK signal is present. Note that the BT band is 300-3400Hz, the Bellcore

band is 200-3200Hz.

AC Electrical Characteristics are over recommended operating conditions, unless otherwise stated.
Typical figures are at 25°C and are for design aid only: not guaranteed and not subject to production testing.

a. dBV = decibels above or below a reference voltage of 1Vrms.
b. dBm = decibels above or below a reference power of 1mW into 600 ohms. 0dBm = 0.7746Vrms.

Electrical Characteristics

- Gain Setting Amplifier

Characteristics

Sym

Min

Typ

Max

Units

Test Conditions

Input Leakage Current

Input Resistance

Input Offset Voltage

Power Supply Rejection Ratio

PSRR

1kHz ripple on V

Common Mode Rejection

CMRR

CMmin

CMmax

DC Open Loop Voltage Gain

VOL

Unity Gain Bandwidth

0.3

MHz

Output Voltage Swing

0.5

-0.5

Load

50k

Maximum Capacitive Load (GS)

100

10 Maximum Resistive Load (GS)

Common Mode Range Voltage

1.0

-1.0

AC Electrical Characteristics

- FSK Detection

Characteristics

Sym

Min

Typ

Max

Units

Notes*

Input Detection Level

-40

-37.78

10.0

-8

-5.78

398.1

dBV

dBm

mVrms

Transmission Rate

1188

1200

1212

baud

Input Frequency Detection

Bell 202 1 (Mark)
Bell 202 0 (Space)

CCITT V.23 1 (Mark)
CCITT V.23 0 (Space)

1188

2178

1280.5
2068.5

1200
2200

1300
2100

1212
2222

1319.5
2131.5

Hz
Hz

Input Noise Tolerance

SNR

FSK

1,2

Preliminary Information

MT8843

5-37

Figure 15 - Input and Output Timing for BT Caller Display Service (CDS), e.g., CLIP

Notes:
1) By choosing t

=15ms, t

ABS

will be 15-25ms so that the current wetting pulse and AC load can be applied right after the StD falling

edge.

2) SIN227 specifies that the AC and DC loads should be removed between 50-150ms after the end of the FSK signal, indicated by CD

returning to high. The CNIC2 may also be powered down at this time.

3) FSKen should be set low when FSK is not expected to prevent the FSK demodulator from reacting to other in-band signals such as

speech, tone alert signal and DTMF tones.

4) TRIGout is the ring envelope during ringing.
5) The total recognition time is t

REC

= t

+ t

, where t

is the tone present guard time and t

is the tone present detect time (refer

to section "Dual Tone Detection Guard Time" on page 25 for details).

6) The total tone absent time is t

ABS

= t

+ t

, where t

is the tone absent guard time and t

is the tone absent detect time (refer

to section "Dual Tone Detection Guard Time" on page 25 for details).
V

TGt

is the comparator threshold (refer to Figure 4).

Line Reversal

Alerting Signal

Ch. seizure

Mark

Data Packet

Ring

..101010..

Data

REC

ABS

(Note 1)

20±5ms

Zss (Refer to SIN227)

< 0.5mA (optional)

<120

Note 2

TGt

Note 4

Note 3

A/B Wires

TRIGout

PWDN

ESt

St/GT

StD

TE DC load

TE AC load

FSKen

DCLK

DATA

OSCout

100ms

B = 88-110ms

45ms (up to 5sec)

D = 80-262ms

E = 45-75ms

2.5sec (typ. 500ms)

G > 200ms

Note: All values obtained
from SIN227 Issue 1

Note 5

Note 6

50-150ms

15±1ms

Current wetting pulse (see SIN227)

Preliminary Information

MT8843

5-39

Figure 17 - Input and Output Timing for Bellcore On-hook Data Transmission Associated with

Ringing, e.g., CID

Notes:
This on-hook case application is included because a CIDCW (off-hook) CPE should also be capable of receiving on-hook data
transmission (with ringing) from the end office. TR-NWT-000575 specifies that CIDCW will be offered only to lines which subscribe to
CID.
1) The CPE designer may choose to enable the CNIC2 only after the end of ringing to conserve power in a battery operated CPE. CD is not

activated by ringing.

2) The CPE designer may choose to set FSKen always high while the CPE is on-hook. Setting FSKen low prevents the FSK

demodulator from reacting to other in-band signals such as speech, CAS or DTMF tones.

3) The microcontroller in the CPE powers down the CNIC2 after CD has become inactive.
4) The microcontroller times out if CD is not activated.

1st Ring

2nd Ring

Ch. seizure

Mark

Data Packet

..101010..

Data

Note 1

Note 2

Note 3

Note 1

Note 4

TIP/RING

TRIGout

PWDN

OSCout

FSKen

DCLK

DATA

A = 2sec typical
B = 250-500ms
C = 250ms
D = 150ms
E = feature specific
Max C+D+E = 2.9 to 3.7sec
F

200ms

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