Preliminary

AS2520/21/20B/21B

Rev. 5.1

Page 3

May 1999

19

22

M1

M2

AI

Microphone Inputs

Differential inputs for handset microphone (electret).

20

21

M4

M3

AI

Handsfree Microphone Inputs

These are the input pins for the handsfree microphone (electret).

23

VOL

D/AI

Volume Control Input

Volume control for the receive signal.

AS2520: Digital control with +/– keys or from µC;

AS2521: Analogue dc control with potentiometer.

24

SS

AO

Supply Source Control Output

This N-channel open drain output controls the external high power source

transistor for supplying (V

loudhearing/handsfree mode.

25

CS

AO

Current Shunt Control Output

This N-channel open drain output controls the external high power shunt

transistor for the modulation of the line voltage and for shorting the line

during make period of pulse dialling.

26

V

SS

Supply

Negative Power Supply

27

LI

AI/O

Line Input

This input is used for power extraction and line current sensing.

28

RI

AI

Receive Input

This is the input for the receive signal.

DI:

Digital Input

AI:

Analogue Input

DO:

Digital Output

AO:

Analogue Output

DI/O:

Digital Input/Output

AI/O:

Analogue Input/output

Operating Modes

I/O Pins

Digital Inputs

Tone Input

Outputs

MODE

HS

LE

PD

MT

TI

CM

LI

RO

LO

Idle (on-hook)

0

0

0

0

Not connected

Low

-

PD

PD

Ringing

0

0

1

0

PDM signal to LO (DI)

SW

-

-

‘TI’

POT

1

0

0

0

Not connected

Low

‘M1/M2’

‘RI/STB’

-

POT/pulse dialling

1

0

1

1

Not connected

Low

V

BE

-

-

POT/DTMF dialling

1

0

0

1

DTMF to LI and RO (AI)

Low

‘TI’

‘TI’

-

Handsfree

0

1

0

0

Not connected

Low

‘M3/M4’

‘RI/STB’

‘LSI’

Handsfree/pulse dial

0

1

1

1

Not connected

Low

V

BE

-

Handsfree/DTMF dial

0

1

0

1

DTMF to LI and RO (AI)

Low

‘TI’

‘LSI’

Loudhearing

1

1

0

0

Not connected

Low

‘M1/M2’

‘RI/STB’

‘LSI’

Loudhearing/pulse dial

1

1

1

1

Not connected

Low

V

BE

Loudhearing/DTMF dial

1

1

0

1

DTMF to LI and RO (AI)

Low

‘TI’

‘LSI’

TAM without LSP

1

0

1

0

Signal to LI (AI)

Low

‘RI/STB’

TAM with LSP

1

1

1

0

Signal to LI (AI)

Low

‘RI/STB’

‘LSI’

Melody feedback

0

1

1

0

PDM signal to LO (DI)

Low

‘RI/STB’

Test mode 1

0

0

0

1

Reserved for testing

Test mode 2

0

0

1

1

Reserved for testing

Table 1: Operating Modes