Pin Description

Pin Name

I/O

Internal

Connection

Description

C1~C5

R1~R4

I/O

CMOS

IN/OUT

These pins form a 4

´5 keyboard matrix which can perform keyboard input detection

and dialing specification setting functions. When on-hook (HKS=high) all the pins are

set high. While off-hook the column group (C1~C5) remains low and the row group

(R1~R4) is set high for key input detection.

An inexpensive single contact 4

´5 keyboard can be used as an input device.

Pressing a key connects a single column to a single row, and actuates the system os-

cillator 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. Refer to the key-

board information for keyboard arrangement and to the functional description for dial-

ing specification selection.

X1

I

OSCILLATOR

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

resonator 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 detected.

X2

O

XMUTE

O

NMOS OUT

XMUTE is an NMOS open drain structure pulled to VSS during dialing signal

transmission. Otherwise, it is an open circuit. XMUTE is used to mute the speech

circuit when transmitting the dial signal.

HKS

I

CMOS IN

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

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

HKS=VDD: On-hook state (PO=low). Except for HFI/HDI

(hand-free/hold-line control input), other functions are all disabled.

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

receive the key input.

PO

O

CMOS OUT

This pin is a CMOS output structure which by receiving the HKS and HFO/HDO

signals, control the dialer to connect or disconnect the telephone line.

PO outputs a low to break line when HKS is high (on-hook) and HFO/HDO is low.

PO outputs a high to make line when HKS is low (off-hook) or HFO is high or HDO

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 high.

MODE

I/O

CMOS

IN/OUT

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

mode or Pulse mode, 10pps/20pps

MODE=VDD: Pulse mode, 10pps

MODE=OPEN: Pulse mode, 20pps

MODE=VSS: Tone mode

During the pulse mode dialing, switching this pin to the tone mode changes the

subsequent digit entry to tone mode. When the chips are in tone mode, switching

to pulse mode will also be recognized.

DTMF

O

CMOS OUT

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

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

amplifier circuit. The load resistor should not be less than 5k

W.

HDI

I

CMOS IN

Pull-High

This pin is a Schmitt trigger input structure. Active low. Applying a negative going

pulse to this pin can toggle the HDO output once.

An external RC network is recommended for input debouncing. The pull-high re-

sistance is 200k

W typ.

HDO

O

CMOS OUT

The HDO is a CMOS output structure. Its output is toggle- controlled by a negative

transition on HDI. When HDO is toggled high, PO keeps high to hold the line. The

hold function can be released by setting HFO high or by an on/off hook operation

or by another HDI input. Refer to the functional description for the hold-line func-

tion.

HT9315 Series

Rev. 1.20

3

October 1, 2002