Pin Name

I/O

Internal

Connection

Description

RBK/KEY2

O

CMOS OUT

CPTD mode: RBK=HIGH: The detected input signal is a

ringback tone.

ABRC mode: Transmission gate input or output pin. Used to

trigger the row and column pin of the redial key when a dial

tone is received. It will output a 100ms pulse.

DIAL/KEY1

O

CMOS OUT

CPTD mode: DIAL=HIGH; The detected input signal is a

dial tone.

ABRC mode: Transmission gate input or output pin. Used to

trigger the row and column pin of the redial key when a dial

tone is received. It will output a 100ms pulse.

EN/KEY

I

CMOS IN

pins are pulled low or high impedance.

ABRC mode: The pin is schmitt trigger input structure.

Active low. Applying a negative going pulse to this pin can

toggle the auto-busy-redial function.

CLR

I

CMOS IN

When CLR is low and BREAK is high, the tone decoder is

reset. This pin can be connected to the mute pin of the dialer

IC for tone elimination.

X1

I

OSCILLATOR

The system oscillator consists of an inverter, a bias resistor

and the necessary load capacitor on-chip. Connect a standard

32.768kHz crystal or ceramic resonator.

X2

O

OSCILLATOR

X1 and X2 terminals implement the oscillator function.

The oscillator is turned off in the standby mode, and is

actuated whenever a keyboard entry is detected.

TEST

I

CMOS IN

Pull-low

For testing only, active high

Approximate internal connection circuits

HT9020

4

21st Aug ’98