MITEL MH8843AE, MH8843AS Datasheet
5-21
Features
• Compatible with B riti sh Telecom (BT) SIN227 &
SIN242, Cable Television Association (CTA)
TW/P&E/312, and Bellcore TR-NWT-000030 &
SR-TSV-002476
• Ring and lin e revers al de tectio n
• Bellcore "CP E Alert ing Si gnal (C AS) " and B T
"Idle State Tone Alert Signal" d etecti on
• 1200 baud BELL 202 and CCITT V.23
Frequenc y Shift K eying (FSK) demo dulati on
• High input sensi tivity
• Dual mode 3 -wire da ta in terface
• Low power CMO S wi th powerd ow n mode
• Input gain ad jus table 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
• Database qu ery an d Co mpute r 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-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.
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
TRIGRCTRIGin
DATA
DR
DCLK
MODE
FSKen
CD
CAP
OSCin OSCout
IN+
IN-
GS
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 Identif ica tion Circuit 2
CMOS
Preliminary Information
Preliminary Information MT8843
5-23
18 DR 3-wire FSK Interface Data Ready (CMOS Output). Active low.This output goes low after
the last DCLK pu lse of eac h word. Th is ident ifies the data (8 -bit word ) bound ary on the
serial output strea m. Typically, DR
is used to latch 8 -bi t words from th e serial -to-para llel
converte r into a m icrocon trol ler.
19 CD
Carrier Detect (CMOS Output). Active low. A logic low indicates the presence of in-band
signal at the ou tput of t he FSK band pass f ilter.
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 quali fied al ert sig nal ha s bee n det ected .
22 ESt Dual Tone Alert Signal Ea rly Ste ering Outp ut. Alert signa l det ection ou tput. Used in
conjuncti on with S t/G T and ex terna l circui try to im pleme 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
TGt
detected at St causes the de vice to regist er the detected to ne
pair and update the output latch. A voltage less than V
TGt
frees the d evic e to acc ept a
new tone pa ir. The GT outpu t acts to re set th e ex ternal steerin g tim e-constant ; its stat e is
a functio n of ESt and t he voltag e o n St.
24 V
DD
Positive Power Supply.
Pin Description
Pin # Nam e 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 microcontrolle r.
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-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.
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 VT+, TRIGRC is
pulled low as C3 discharges. TRIGout
stay s 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 sle ep mode to c o n se r v e po w e r.
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.
a. The off -ho ok s ig na l le ve l i s - 15 dB m to - 34 dB m pe r to ne to b e
specifie d in the BT C ID C W s pe c ifi ca tion in th e fut ur e .
b. The si gn al po wer i s e xp res s ed in dBm r ef ere nc ed to 600 ohm
at the CPE A/B (tip/r ing) int erf ace.
c. ASL = ac ti ve s pe ec h le ve l ex pressed in dB m r efe r en c 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 e as ur e d
according to method B of Recommendation P.56 "Objective
Measurem e nt of Activ e S pe e ch Level " pu bl 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 it ion time sh ou ld be n ot less
than 20m s if both ton es a re de te cted.
Item BT 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
a
(0.22dBm
b
to
-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
c
near end speech
Duration 88ms to 110ms
d
75ms to 85ms
Speech
present
No Yes
Table 1. Dual Tone Alert Signal Ch arac teri stics
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 Aler ti ng Si g 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
REC
= tGP + tDP, where
t
GP
is the tone present guard time and tDP 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
= tGA + tDA, where
t
GA
is the tone absent guard time and tDA 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 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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