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 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.

19

CD

Carrier Detect (CMOS Output). Active low. A logic low indicates the presence of in-band

signal at the output of the FSK bandpass 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 qualified alert signal has been detected.

22

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.

23

St/GT

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

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.

24

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.