4-248

CD22202, CD22203

FIGURE 2. CRYSTAL OSCILLATOR

HEX/B28

This pin selects the format of the digital output code. When

HEX/B28 is tied high, the output is hexadecimal. When tied

low, the output is binary coded 2-of-8. The following table

describes the two output codes.

ED

This pin, on the CD22203 only, indicates the presence of fre-

quencies which are likely to be DTMF digits, but have not yet

been verified by a DV signal. It is comparable to a “button-

down” output, and it is useful as an EARLY DETECT signal to

interrupt a microprocessor for digit storage and validation.

DV and CLRDV

DV signals a detection by going high after a valid tone pair is

sensed and decoded at the output pins D1, D2, D4, and D8.

DV remains high until a valid pause occurs or CLRDV is

raised high, whichever is sooner. This handshake can save

microprocessor time.

DTMF Dialing Matrix

IN1633

When tied high, this pin inhibits detection of tone pairs con-

taining the 1633Hz component. For detection of all 16 stan-

dard digits, IN1633 must be tied low.

N/C Pin

This pin has no internal connection and should be left floating.

Digital Inputs and Outputs

All digital inputs and outputs of the DTMF receivers are rep-

resented by the schematic below. Only the “analog in” pin is

different, and is described above. Care must be exercised

not to exceed the voltage or current ratings on these pins as

listed in the “maximum ratings” section.

FIGURE 3. DIGITAL INPUTS AND OUTPUTS

Input Filter

The CD22202 and CD22203 will tolerate total input noise of

a maximum of 12dB below the lowest amplitude tone. For

most telephone applications, the combination of the high

frequency attenuation of the telephone line and internal

band limiting make special circuitry at the input to these

receivers unnecessary. However, noise near the 56kHz

internal sampling frequency will be aliased (folded back)

into the audio spectrum, so if excessive noise is present

TABLE 1. OUTPUT CODES

DIGIT

HEXADECIMAL

BINARY CODED 2-OF-8

D8

D4

D2

D1

D8

D4

D2

D1

1

00010000

2

00100001

3

00110010

4

01000100

5

01010101

6

01100110

7

01111000

8

10001001

9

10011010

0

10101101

*

10111100

#

11001110

A

11010011

B

11100111

C

11111011

D

00001111

XEN

XEN

CD22202/22203

12

11

8

13

ATB

XIN

3.579545MHz

XOUT

1M

12

13

8

UP TO 10 DEVICES

CD22202/22203

COL 0

1209Hz

COL 1

1336Hz

COL 2

1477Hz

COL 3

1633Hz

ROW 0

697Hz

ROW 1

770Hz

ROW 2

852Hz

ROW 3

941Hz

NOTE: Column 3 is for special applications and is not normally used

in telephone dialing.

1

2

3

A

4

5

6

B

7

8

9

C

*

0

#

D

CMOS

DIGITAL

CIRCUITRY

DIGITAL

OUTPUT

DIGITAL

INPUT