MT88E45

4-Wire Calling Number Identification Circuit 2

(4-Wire CNIC2)

Features

Compatible with:

· Bellcore GR-30-CORE, SR-TSV-002476,

ANSI/TIA/EIA-716, draft TIA/EIA-777;

· ETSI ETS 300 778-1 (FSK only variant) & -2;
· BT (British Telecom) SIN227 & SIN242

Bellcore `CPE Alerting Signal' (CAS), ETSI `Dual
Tone Alerting Signal' (DT-AS), BT Idle State and
Loop State `Tone Alert Signal' detection

1200 baud Bell 202 and CCITT V.23 FSK
demodulation

Separate differential input amplifiers with
adjustable gain for Tip/Ring and telephone hybrid
or speech IC connections

Selectable 3-wire FSK data interface (bit stream
or 1 byte buffer)

Facility to monitor the stop bit for framing error
check

FSK Carrier detect status output

3 to 5V +/- 10% supply voltage

Uses 3.579545MHz crystal or ceramic resonator

Low power CMOS with power down

Applications

Bellcore CID (Calling Identity Delivery) and
CIDCW (Calling Identity Delivery on Call
Waiting) telephones and adjuncts

ETSI, BT CLIP (Calling Line Identity
Presentation) and CLIP with Call Waiting
telephones and adjuncts

Fax and answering machines

Computer Telephony Integration (CTI) systems

Description

The MT88E45 is a low power CMOS integrated circuit
suitable for receiving the physical layer signals used
in North American (Bellcore) Calling Identity Delivery
on Call Waiting (CIDCW) and Calling Identity Delivery
(CID) services. It is also suitable for ETSI and BT
Calling Line Identity Presentation (CLIP) and CLIP
with Call Waiting services.

The MT88E45 contains a 1200 baud Bell 202/CCITT
V.23 FSK demodulator and a CAS/DT-AS detector.
Two input op-amps allow the MT88E45 to be
connected to both Tip/Ring and the telephone hybrid
or speech IC receive pair for optimal CIDCW
telephone

architectural

implementation.

FSK

demodulation is always on Tip/Ring, while CAS
detection can be on Tip/Ring or Hybrid Receive. Tip/
Ring

CAS

detection

required

for

Bellcore's

proposed Multiple Extension Interworking (MEI) and
BT's on-hook CLIP. A selectable FSK data interface
allows the data to be processed as a bit stream or
extracted from a 1 byte on chip buffer. Power
management has been incorporated to power down
the FSK or CAS section when not required. Full chip
power down is also available. The MT88E45 is
suitable for applications using a fixed power source
(with a +/-10% variation) between 3 and 5V.

Figure 1 - Functional Block Diagram

Anti-Alias
Filter

FSK
Bandpass

FSK
Demodulator

Data Timing
Recovery

Carrier
Detector

2130Hz
Bandpass

2750Hz
Bandpass

Tone
Detection
Algorithm

FSKen+Tip/Ring CASen

Hybrid CASen

Guard
Time

STD

Bias
Generator

Oscillator

Control Bit
Decode

FSKen

CASen

PWDN

IN1+

IN1-

GS1

IN2+

IN2-

GS2

REF

OSC1

OSC2

CB0

CB2

CB1

DATA

DCLK

DR/STD

ST/GT

EST

Vdd
Vss

MODE

FSKen

CASen

PWDN

DS5143

ISSUE 3

September 2001

Advance Information

Ordering Information

MT88E45AS

20 Pin SOIC

MT88E45AN

20 Pin SSOP

-40

°C to 85°C

MT88E45

Advance Information

Figure 2 - Pin Connections

Pin Description

Pin #

Name

Description

REF

Voltage Reference (Output). Nominally Vdd/2. It is used to bias the Tip/Ring and Hybrid input op-
amps.

IN1+

Tip/Ring Op-amp Non-inverting (Input).

IN1-

Tip/Ring Op-amp Inverting (Input).

GS1

Tip/Ring Gain Select (Output). This is the output of the Tip/Ring connection op-amp. The op-
amp should be used to connect the MT88E45 to Tip and Ring. The Tip/Ring signal can be
amplified or attenuated at GS1 via selection of the feedback resistor between GS1 and IN1-. FSK
demodulation (which is always on Tip/Ring) or CAS detection (for MEI or BT on-hook CLIP) of the
GS1 signal is enabled via the CB1 and CB2 pins. See Tables 1 and 2.

Vss

Power supply ground.

OSC1 Oscillator (Input). Crystal connection. This pin can also be driven directly from an external clock

source.

OSC2 Oscillator (Output). Crystal connection. When OSC1 is driven by an external clock, this pin

should be left open.

CB0

Control Bit 0 (CMOS Input). This pin is used primarily to select the 3-wire FSK data interface
mode. When it is low, interface mode 0 is selected where the FSK bit stream is output directly.
When it is high, interface mode 1 is selected where the FSK byte is stored in a 1 byte buffer which
can be read serially by the application's microcontroller.
The FSK interface is consisted of the DATA, DCLK and DR/STD pins. See the 3 pin descriptions
to understand how CB0 affects the FSK interface.
When CB0 is high and CB1, CB2 are both low the MT88E45 is put into a power down state
consuming minimal power supply current. See Tables 1 and 2.

DCLK

3-wire FSK Interface Data Clock (Schmitt Input/CMOS Output). In mode 0 (when the CB0 pin
is logic low) this is a CMOS output which denotes the nominal mid-point of a FSK data bit.
In mode 1 (when the CB0 pin is logic high) this is a Schmitt trigger input used to shift the FSK data
byte out to the DATA pin.

REF

IN1+

IN1-

GS1

Vss

OSC1

DCLK

DATA

IN2+

IN2-

GS2

CB2

CB1

Vdd

ST/GT

MT88E45

OSC2

CB0

EST

DR/STD

Advance Information

MT88E45

DATA

3-wire FSK Interface Data (CMOS Output). Mark frequency corresponds to logical 1. Space
frequency corresponds to logical 0.
In mode 0 (when the CB0 pin is logic low) the FSK serial bit stream is output to the DATA pin
directly.
In mode 1 (when the CB0 pin is logic high) the start bit is stripped off, the data byte and the trailing
stop bit are stored in a 9 bit buffer. At the end of each word signalled by the DR/STD pin, the
microcontroller should shift the byte out onto the DATA pin by applying 8 read pulses to the DCLK
pin. A 9th DCLK pulse will shift out the stop bit for framing error checking.

DR/STD 3-wire FSK Interface Data Ready/CAS Detection Delayed Steering (CMOS Output). Active

low.
When FSK demodulation is enabled via the CB1 and CB2 pins this pin is the Data Ready output.
It denotes the end of a word. In both FSK interface modes 0 and 1, it is normally hi and goes low
for half a bit time at the end of a word. But in mode 1 if DCLK starts during DR low, the first rising
edge of the DCLK input will return DR to high. This feature allows an interrupt requested by a low
going DR to be cleared upon reading the first DATA bit.
When CAS detection is enabled via the CB1 and CB2 pins this pin is the Delayed Steering output.
It goes low to indicate that a time qualified CAS has been detected.

EST

CAS Detection Early Steering (CMOS Output). Active high. This pin is the raw CAS detection
output. It goes high to indicate the presence of a signal meeting the CAS accept frequencies and
signal level. It is used in conjunction with the ST/GT pin and external components to time qualify
the detection to determine whether the signal is a real CAS.

ST/GT CAS Detection Steering/Guard Time (CMOS Output/Analog Input). It is used in conjunction

with the EST pin and external components to time qualify the detection to determine whether the
signal is a real CAS.
A voltage greater than V

TGt

at this pin causes the MT88E45 to indicate that a CAS has been

detected by asserting the DR/STD pin low. A voltage less than V

TGt

frees up the MT88E45 to

accept a new CAS and returns DR/STD to high.

Carrier Detect (CMOS Output). Active low.
A logic low indicates that an FSK signal is present. A time hysteresis is provided to allow for
momentary signal discontinuity. The demodulated FSK data is inhibited until carrier detect has
been activated.

Vdd

Positive power supply.

CB1

Control Bit 1 (CMOS Input). Together with CB2 this pin selects the MT88E45's functionality
between FSK demodulation, Tip/Ring CAS detection and Hybrid CAS detection.
When CB0 is high and CB1, CB2 are both low the MT88E45 is put into a power down state
consuming minimal power supply current. See Tables 1 and 2.

CB2

Control Bit 2 (CMOS Input). Together with CB1 this pin selects the MT88E45's functionality
between FSK demodulation, Tip/Ring CAS detection and Hybrid CAS detection.
When CB0 is high and CB1, CB2 are both low the MT88E45 is put into a power down state
consuming minimal power supply current. See Tables 1 and 2.

GS2

Hybrid Gain Select (Output). This is the output of the hybrid receive connection op-amp. The op-
amp should be used to connect the MT88E45 to the telephone hybrid or speech IC receive pair.
The hybrid receive signal can be amplified or attenuated at GS2 via selection of the feedback
resistor between GS2 and IN2-. When the CPE is off-hook CAS detection of the GS2 signal
should be enabled via the CB1 and CB2 pins. See Tables 1 and 2.

IN2-

Hybrid Op-amp Inverting (Input).

IN2+

Hybrid Op-amp Non-Inverting (Input).

Pin Description (continued)

Pin #

Name

Description

MT88E45

Advance Information

Functional Overview

The MT88E45 is compatible with FSK and FSK plus
CAS (CPE Alerting Signal) based Caller ID services
around the world. Caller ID is the generic name for a
group of services offered by telephone operating
companies whereby information about the calling
party is delivered to the subscriber. In Europe and
some other countries Caller ID is known as Calling
Line Identity Presentation (CLIP). ETSI calls CAS
`Dual Tone Alerting Signal' (DT-AS), BT calls it `Tone
Alert Signal'.

Depending on the service, data delivery can occur
when the line is in the on-hook or off-hook state. In
most countries the data is modulated in either Bell
202 or CCITT V.23 FSK format and transmitted at
1200 baud from the serving end office to the
subscriber's

terminal.

Additionally

off-hook

signalling, the special dual tone CAS is used to alert
the terminal before FSK data transmission. BT uses
CAS to alert the terminal prior to FSK in both on-
hook

(Idle

State)

and

off-hook

(Loop

State)

signalling.

Table 1 - CB0/1/2 Functionality

The number of control bits (CB) required to interface the MT88E45 with the microcontroller depends on the
functionality of the application, as shown in Table 2.

Table 2 - Control Bit Functionality Groups

CB0 CB1 CB2

FSK

Interface

Function

0/1

Set by CB0 FSK Demodulation. Tip/Ring input (GS1) selected. DR/STD is DR.

0/1

Set by CB0 Hybrid CAS Detection. Hybrid Receive input (GS2) selected. DR/STD is STD.

0/1

Set by CB0 Tip/Ring CAS Detection. Tip/Ring input (GS1) selected. DR/STD is STD.

When the line is off-hook, a Bellcore Multiple Extension Interworking (MEI)
compatible Type 2 CPE should be able to detect CAS from Tip/Ring while the
CPE is on-hook because it may be the ACK sender. Tip/Ring CAS detection is
also required for BT's on-hook CLIP.

Mode 1

Power Down. The MT88E45 is disabled and draws virtually no power supply
current.

Mode 0

Reserved for factory testing.

Functionality Group

Control

Description

FSK (mode 0 or 1) and
Hybrid CAS only
(Non MEI compatible)

CB2

CB0 is hardwired to Vdd or Vss to select the FSK
interface.
CB1 hardwired to Vdd.
The microcontroller uses CB2 to select between the 2
functions.

FSK (mode 0 or 1),
Hybrid CAS,
Tip/Ring CAS
(MEI compatible or BT on-hook CLIP)

CB1
CB2

CB0 is hardwired to Vdd or Vss to select the FSK
interface.
The microcontroller uses CB1 and CB2 to select between
the 3 functions.

FSK (mode 1),
Hybrid CAS,
Tip/Ring CAS,
Power Down
(MEI compatible or BT on-hook CLIP)

CB1
CB2

CB0 is hardwired to Vdd to select FSK interface mode 1.
The microcontroller uses CB1 and CB2 to select between
the 4 functions.

FSK (mode 0), Hybrid CAS,
Tip/Ring CAS, Power Down
(MEI compatible or BT on-hook CLIP)

CB0
CB1
CB2

All 3 pins are required.

Advance Information

MT88E45

In North America, Caller ID uses the voiceband data
transmission

interface

defined

the

Bellcore

document GR-30-CORE. The terminal or CPE
(Customer Premises Equipment) requirements are
defined

Bellcore

document

SR-TSV-002476.

Typical services are CND (Calling Number Delivery),
CNAM

(Calling

Name

Delivery),

VMWI

(Visual

Message Waiting Indicator) and CIDCW (Calling
Identity Delivery on Call Waiting).

In Europe, Caller ID requirements are defined by
ETSI. The CPE documents are ETS 300 778-1 for
on-hook, ETS 300 778-2 for off-hook. The end office
requirements are ETS 300 659-1 (on-hook) and ETS
300 659-2 (off-hook). ETSI has defined services
such as CLIP and CLIP with Call Waiting which are
similar

those

Bellcore.

Some

European

countries produce their own national specifications.
For example, in the UK BT's standards are SIN227
and SIN242, the UK CCA (Cable Communications
Association) standard is TW/P&E/312.

In on-hook Caller ID, such as CND, CNAM and CLIP,
the information is typically transmitted (in FSK) from
the end office before the subscriber picks up the
phone. There are various methods such as between
the first and second rings (North America), between
an abbreviated ring and the first true ring (Japan,
France and Germany). On-hook Caller ID can also
occur without ringing for services such as VMWI. In
BT's on-hook CLIP, the signalling begins with a line
polarity reversal, followed by CAS and then FSK.
Bellcore calls an on-hook capable Caller ID CPE a
`Type 1 CPE'.

In off-hook Caller ID, such as CIDCW and CLIP with
Call Waiting, information about a new calling party is
sent to the subscriber who is already engaged in a
call. Bellcore's method uses CAS to alert the CPE.
When the CPE detects CAS and there are no off-
hook

extensions,

the

CPE

should

mute

its

transmission path and send an acknowledgment to
the end office via a DTMF digit called ACK. Upon
receiving ACK, the end office will send the FSK data.
Bellcore calls an off-hook capable CPE a `Type 2
CPE'. A Type 2 CPE is capable of off-hook and Type
1 functionalities and should ACK with a DTMF `D'.
The ETSI and BT off-hook signalling protocols are
similar to Bellcore's but with timing and signal
parametric differences. ETSI has no requirement for
off-hook extension checking before ACK.

One factor affecting the quality of the CIDCW service
is the CPE's CAS speech immunity. Although the
end office has muted the far end party before and
after it sends CAS, the near end (the end which is to
receive the information) user may be still talking.
Therefore the CPE must be able to detect CAS

successfully in the presence of near end speech.
This is called the talkdown immunity. The CPE must
also be immune to imitation of CAS by speech from
both ends of the connection because the CAS
detector

continuously

exposed

speech

throughout the call. This is called

the talkoff

immunity.

If the CPE is a telephone, one way to achieve good
CAS speech immunity is to put CAS detection on the
telephone hybrid or speech IC receive pair instead of
on Tip and Ring. Talkdown immunity improves
because the near end speech has been attenuated
while the CAS level is the same as on Tip/Ring,
resulting in improved signal to speech ratio. Talkoff
immunity is also improved because the near end
speech has been attenuated.

In the present Bellcore off-hook protocol, the CPE
should not ACK if it detected an off-hook extension.
The FSK will not be sent and the customer will not
receive a paid for service. Bellcore, in conjunction
with

the

TIA

(Telecommunications

Industry

Association) TR41.3.1 working group, has defined a
CPE

capability

called

Multiple

Extension

Interworking (MEI) which will overcome this problem.

In the MEI scheme, all MEI compatible CPE's must
be capable of detecting CAS when the line is off-
hook, even though the CPE itself may be on-hook.
This is because under some conditions an on-hook
CPE may become the ACK sender. Another reason
for the on-hook CPE to detect CAS is to maintain
synchronous call logs between on and off-hook
CPEs. When CAS is received and all off-hook CPEs
are MEI compatible, one of the CPEs will ACK and
all compatible sets will receive FSK.

A problem arises in a CPE where the CAS detector
is connected only to the hybrid or speech IC receive
pair: it cannot detect CAS when it is on-hook. The
reason is that when the CPE is on-hook either the
hybrid/speech IC is non functional or the signal level
is severely attenuated. Therefore an on-hook Type 2
CPE must be capable of detecting CAS from Tip/
Ring, in addition to detecting CAS from the hybrid/
speech IC receive signal when it is off-hook.

The MT88E45 offers an optimal solution which
combines

good

speech

immunity

and

MEI

compatibility. Two input op-amps allow the MT88E45
to be connected both to Tip/Ring and to the hybrid/
speech IC receive pair. Both connections can be
differential or single ended. FSK demodulation is
always on the Tip/Ring signal. CAS detection can be
from the Tip/Ring or hybrid/speech IC receive signal.

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