L3924AN datasheet(3/15 Pages) STMICROELECTRONICS

Part #	L3924AN

Description	SPEECH AND 14 MEMORY DIALER WITH HOLD FUNCTION

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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A valid keypad entry is either a single Row con-

nected to a single Column or GND simultaneously

presented to both a single Row and a single Col-

unm.

In its quiescent or standby state, during normal

off-hook operation, either the Rows or the Col-

umns are at logic level 1 (VDD). Pulling one input

low enables the on chip oscillator. Keyboard

scanning then begins.

Scanning consists of Rows and Columns alter-

nately switching high through on chip pullups. Af-

ter both a Row and Column key have been de-

tected, the debounce counter is enabled and any

noise (bouncing contacts, etc) is ignored for a de-

bounce period (TKD) of 32ms. At this time, the

keyboard is sampled and if both the Row and Col-

umn information are valid, the information is buff-

ered into the LND location. After scanning starts,

the row and column inputs will assume opposite

states.

In the tone mode, if two or more keys in the same

row or if two or more keys in the same column are

depressed a single tone will be output. The tone

will corresponds to the row or column for which

the two keys were pushed. This feature is for test-

ing purposes, and single tone will not be redialed.

Also in the tone mode, the output tone is continu-

ous in the manual dialing as long as the key is

pushed. The output tone duration follows the Ta-

ble 1. When redialing in the tone mode, each

DTMF output has 100ms duration, and the tone

separation (inter signal delay) is 100ms.

Table 1: Output Tone Duration

Key-Push Time, T

Tone Output

T<= 32ms

32ms < = T < = 100ms +

Tkd

T > = 100ms + Tkd

No output, ignored by

one chip phone.

100ms Duration

Output Duration = T - Tkd

OSC

Output. 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

(pin 8). The nominal resonator frequency is

3.579545MHz and any deviation 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 tol-

erance 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-hooked, it will be pulled high by external resis-

tor. The pulse out will go high when the Hold key

is pressed, in this way the phone will stay con-

nected to the line untill the parallel phone is

hooked-OFF or the Hold Key is pressed again.

MODE/PACIFIER TONE

Input (MODE). Pin 7. MODE determines the di-

aler’s default operating mode. When the device is

powered up or the hookswitch input is switched

from on-hook (VDD) to off-hook (GND), the default

determines the signalling mode. A VDD connec-

tion defaults to tone mode operation and a GND

connection 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 * key is depressed. Subsequent * key inputs will

cause the DTMF code for an * to be dialed.. The

softswitch will only switch from pulse to tone. After

returning to on-hook and back to off-hook, the

phone will be in pulse mode. Redial by the LND key

or the MEM key will repeat the softswitch.

Output (PACIFIER TONE). Pin 7. In pulse mode,

all valid key entries activate the pacifier tone. In

tone

mode, any non DTMF entry (FLASH,

PROG, PAUSE, LND, HOLD, MEM, E1, E2 and

E3), activates the pacifier tone. The pacifier tone

provides audible feedback, confirming that key

has been properly entered and accepted. It is a

500Hz square wave activated upon acceptance of

valid key input after the 32ms debounce time. The

square wave terminates after a maximum of

75ms or when the valid key is no longer present.

The pacifier tone signal is simultaneously sent to

earphone and the buzzer. The buzzer can be re-

moved without affecting this function.

HKS

Input. Pin 8. This is the hookswitch input to the one

chip phone. This is a high impedance input and

must be switched high for on-hook operation or low

for off-hook operation. A transition on this input

causes the on chip logic to initialize, terminating

any operation in progress at the time. The signaling

mode defaults to the mode selected at pin 7. Fig-

ures 1 and 2 illustrate the timing for this pin.

GND

Pin 9 is the negative line terminal of the device.

This is the voltage reference for all specifications.

RXOUT, GRX, RXIN

RXOUT (pin 10), GRX (pin 11) and RXIN (pin 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 11dB and 41dB to suit the sen-

sitivity of the earphone used. The amplification is

proportional to the external resistor connected be-

tween GRX and RXOUT.

FUNCTION PIN DESCRIPTION (continued)

L3914A - L3924A - L3934A

3/15

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