Preliminary Information
Pin Description
Pin #
18
Name
DR
Description
MT8843
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.
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.
Dual Tone Alert Signal Delayed Steering Output.
When high, it indicates that a guard
time qualified alert signal has been detected.
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.
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.
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.
19
20
21
22
CD
INT
StD
ESt
23
St/GT
24
V
DD
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
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