ST3917B 查看數據表（PDF） - STMicroelectronics

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ST3917B

SPEECH - TONE/PULSE DIALER - LED INDICATOR

STMicroelectronics 

ST3917A - ST3917B

PIN DESCRIPTION (continued)

SEL (Input, Pin 4)

This is an option selectable pin for four Flash

duration. The four options are summarised in the

table 2.

For option 1, softswitch feature is inhibited. It

means redialed by the LND key in pulse mode will

not repeat the softswitch and subsequent digits,

only pulse digits are dialed out.

Table 2 : Options Selectable for Flash Duration

Options

1

2

3

4

SEL

VDD

GND

Any Row

Any Col

Flash (ms)

100

600

300

100

Softswitch

Inhibited

Enable

Enable

Enable

OSC (Input, Pin 5)

Only one pin is needed to connect the ceramic

resonator to the oscillator circuit. The other end of

the resonator is connected to GND. The nominal

resonator frequency is 3.579545MHz and any de-

viation from this standard is directly reflected in the

Tone output frequencies. The ceramic resonator

provides the time reference for all circuit functions.

A ceramic resonator with tolerance of ±0.25% is

recommended.

PULSE (Output, Pin 6)

This is an output consisting of an open drain N-

channel device. During on-hook, pulse output pin

is in high impedance and once off-hook, it will be

pulled high by external resistor.

MODE/PT (Input, Pin 7)

Input (MODE). MODE determines the dialer’s de-

fault operating mode. When the device is powered

up or the hookswitch input is switched from on-

hook (VDD) to off-hook (GND), the default deter-

mines the signalling mode. A VDD connection

defaults to tone mode operation and a GND con-

nection defaults to pulse mode operation.

When dialing in the pulse mode, a softswitch fea-

ture will allow a change to the tone mode whenever

the * or softswitch key (TONE) is depressed. Sub-

sequent * key inputs will cause the DTMF code for

an * to be dialed. The softswitch will only switch

from pulse to tone. The phone will be in pulse mode

only after returning to on-hook and back to off-

hook. Redialed by the LND key will repeat the

softswitch unless the softswitch redial feature is

inhibited.

Output (PT). Pacifier Tone Output. In pulse mode,

all valid key entries activate the pacifier tone. In

tone mode, any non DTMF entry (FLASH, PAUSE,

LND, TONE) activates the pacifier tone. The paci-

fier tone provides audible feedback, confirmingthat

the key has been properly entered and accepted.

It is a 500Hz square wave activated upon accep-

tance of valid key input after the 32ms debounce

time.

The square wave terminates after 75ms typically or

when the valid key is no longer present. The pacifier

tone signal is simultaneously sent to the earphone

and the buzzer. The buzzer can be removed with-

out affecting this function. The resistor value set on

MODE/PT pin determines the level of the pacifier

tone in the earphone.

HKS (Input, Pin 8)

This is the hookswitch input to the device. It is a

CMOS input with a high pull up internal resistance

and must be switched high or open for on-hook

operation and low for off-hook operation. A transi-

tion on this input causes the on-chip logic to initial-

ize, terminating any operation in progress at the

time. The signalling mode defaults to the mode

selected at MODE/PT pin. Figures 2, 3 and 4, 5

illustrate the timing for this pin.

GND (Pin 9)

GND is the negative line terminal of the device.This

is the voltage reference for all specifications.

RXOUT, GRX, RXIN (Pins 10, 11 and 12)

The receive amplifier has one input RXIN and a non

inverting output RXOUT. Amplification from RXIN

to RXOUT is typically 31dB and it can be adjusted

between 21dB and 41dB to suit the sensitivity of

the earphone used. The amplification is propor-

tional to the external resistor connected between

GRX and RXOUT. For the hearing impaired, a

specific application to offer 17dB additional gain at

3kHz is permitted.

IREF (Pin 13)

An external resistor of 3.6kΩ connected between

IREF and GND will set the internal current level.

Any change of this resistor value will influence the

microphone gain, DTMF gain, earphone gain and

sidetone level.

VCC (Pin 14)

VCC is the positive supply of the speech network. It

can be stabilized by a decoupling capacitor be-

tween VCC and GND. The VCC supply voltage may

also be used to supply external peripheral circuits.

3/16

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