Pin Description

Pin Name

I/O

Internal

Connection

Description

C1~C3

R1~R4

I/O

CMOS

I/O

These pins along with the HKS form a 4

´4 keyboard matrix which can perform key-

board input detection. When on-hook (HKS=high) all the pins are set high. While

off-hook the column group (C1~C3) is set low and the row group (R1~R4) remains

high for input detection.

Pressing a key connects a single row to a single column HKS and actuates the sys-

tem oscillator that results in a dialing signal output. If more than two keys are

pressed at the same time, no response occurs. The key-in debounce time is 20ms.

X1

I

OSC

The system oscillator consists of an inverter, a bias resistor and the necessary load

capacitor on chip. Connecting a standard 3.579545MHz crystal or ceramic resona-

tor to the X1 and X2 terminals can implement the oscillator function. The oscillator is

turned off in the standby mode, and is actuated whenever a keyboard entry is de-

tected.

X2

O

XMUTE

O

NMOS

Open Drain

NMOS open drain structure pulled to VSS during dialing signal transmission. Other-

wise, it is an open circuit. This pin is used to mute the speech circuit when transmit-

ting the dial signal.

HKS

I

CMOS

This pin is used to monitor the status of the hook-switch and its combination with

HFI can control the PO pin output to make or break the line.

HKS=VDD: On-hook state (PO=low). Except for HFI (hand-free control input), other

functions are all disabled.

HKS=VSS: Off-hook state (PO=high). The chip is in the stand-by mode and ready

to receive the key input.

PO

O

NMOS

NMOS open drain output structure, which by receiving the HKS and HFO signals,

control the dialer so as to connect or disconnect the telephone line.

PO is pulled to VSS when HKS is high (on-hook) and HFO is low.

PO is an open circuit which make the line connection when HKS is low (off-hook) or

HFO is high.

During the off-hook state, this pin also outputs the dialing pulse train in pulse mode

dialing. While in the tone mode, this pin is always an open circuit.

MODE

I/O

CMOS

This is a tri-state input/output pin, used for dialing mode selection, either Tone

mode or Pulse mode, 10pps/20pps

MODE=VDD: Pulse, 10pps, M/B=1/2

MODE=Floating: Pulse, 20pps, M/B=1/2

MODE=VSS: Tone.

The MODE selection is checked each time a key input is received.

DTMF

O

CMOS

This pin is active only when the chip transmits tone dialing signals. Otherwise, it al-

ways outputs a low. The pin outputs tone signals to drive the external transmitter

W and any DC

KT

O

NMOS

NMOS open drain structure for keytone output. It outputs 34ms of 600Hz tone burst

when any key is pressed in the pulse mode or when a function key is pressed in the

tone mode.

HFI

I

CMOS

Pulled-high, this pin is a Schmitt trigger input structure. Active low. Applying a nega-

tive going pulse to HFI can toggle the HFO once and hence control the hand-free

function. The pull-high resistance of HFI is about 200k

W typ. An external RC net-

work is recommended for input debouncing.

HFO

O

CMOS

The HFO pin is a CMOS output structure. Its output is toggle- controlled by a nega-

tive transition on HFI pin. When HFO is high, the hand-free function is enabled and

PO outputs a high to connect the line.

The hand-free function can be released by an on-off-hook operation or by another

HFI input. Refer to the functional description for the hand-free functional operation.

VDD

¾¾

Positive power supply, 2.0V~5.5V for normal operation

VSS

¾¾

Negative power supply, ground

MODEO

O

NMOS

NMOS open drain output pin pulled to VSS during tone output and is an open circuit

during pulse output.

HT93214 Series

Rev. 1.10

3

October 2, 2002