U3900BM

Rev. A2, 25-Aug-98

Target Specification

10 (34)

2.2.8

SCWID: Overview

14608

EGT

Alert signal

high-frequency

logic part

Alert signal

low-frequency

logic part

Analog

filter

Analog

filter

2130 Hz

2750 Hz

UGT

DGT

FC

Time guard

Command bits CDE < 0...8 >

from serial bus

Wetting

pulse

W pulse

Alert

To interrupt

system

CLASS

signal

To CLID FSK filter

Figure 8. Alert detection

General information:

All the control bits provided for the SCWID function can be modified at any time with the microprocessor.

2.2.9

CAS Detect Process

Typical application:

The incoming signal from the CO is not polluted with speech or music. (The feature early guard time is not used)

Choice of 4

DGT values

Down guard

time

Interrupt

to the

µP

CAS signal duration: 80

frequencies: 2130 Hz + 2750 Hz

Interrupt

to the

µP

Up guard

time

Choice of 4

UGT values

IN SCWID

detector

OUT SCWID

detector

14609

Figure 9. Timing diagram of standard alert detection

If any drop in the CAS signal occurs before the end of the

UGT specified value, then the time counter restarts and

the OUT SCWID detector remains low.

If any spike in the blank signal occurs before the end of

the DGT specified value, then the time counter restarts

and the OUT SCWID detector remains high.