Tone Decoding

FLOW

FHIGH

Key (ref.)

OE

Q4

Q3

Q2

Q1

697

1209

1

H

0

0

0

1

697

1336

2

H

0

0

1

0

697

1477

3

H

0

0

1

1

770

1209

4

H

0

1

0

0

770

1336

5

H

0

1

0

1

770

1477

6

H

0

1

1

0

852

1209

7

H

0

1

1

1

852

1336

8

H

1

0

0

0

852

1477

9

H

1

0

0

1

941

1336

0

H

1

0

1

0

941

1209

S

H

1

0

1

1

941

1477

#

H

1

1

0

0

697

1633

A

H

1

1

0

1

770

1633

B

H

1

1

1

0

852

1633

C

H

1

1

1

1

941

1633

D

H

0

0

0

0

ANY

ANY

ANY

L

Z

Z

Z

Z

L = logic low, H = logic high, Z = high impedance

M-8870

www.clare.com

5

Rev. 3

Differential Input Configuration

Common Crystal Connection

stops the oscillator and the functioning of the filters.

On the M-8870-01 models, this pin is tied to ground

(logic low).

Inhibit mode is enabled by a logic high input to pin 5

(INH). It inhibits the detection of 1633 Hz. The output

code will remain the same as the previous detected

code (see Pin functions table on page 4). On the M-

8870-01 models, this pin is tied to ground (logic low).

Input Configuration

The input arrangement of the M-8870 provides a dif-

ferential input operational amplifier as well as a bias

source (V

is made for connection of a feedback resistor to the

op-amp output (GS) for gain adjustment.

In a single-ended configuration, the input pins are

connected as shown in the Single - Ended Input

Configuration on page 3 with the op-amp connected

for unity gain and V

The Differential Input Configuration bellow permits

gain adjustment with the feedback resistor R

DTMF Clock Circuit

The internal clock circuit is completed with the addition

of a standard 3.579545 MHz television color burst crys-

tal. The crystal can be connected to a single M-8870 as

shown in the Single - Ended Input Configuration on

page 3, or to a series of M-8870s. As illustrated in the

Common Crystal Connection below, a single crystal

can be used to connect a series of M-8870s by cou-

pling the oscillator output of each M-8870 through a 30

pF capacitor to the oscillator input of the next M-8870.