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ST3917B

SPEECH - TONE/PULSE DIALER - LED INDICATOR

STMicroelectronics 

ST3917A - ST3917B

DEVICE OPERATION (continued)

Led Indicator / Tone Mode Indication

When the MU/MFI (Pin 24) is connected to any row

of the keypad input, the LED connected to Pin 15

(LED) becomes a Tone mode indicator.

The LED indicator is used in the following conditions :

- At Tone mode, LED will light up at off-hook. The

LED will turn off only when the telephone goes

on-hook.

Example : Tone mode

OFF-HOOK (LED turns on) <TONE> D1, D2, D3

ON-HOOK (LED turns off)

OFF-HOOK (LED turns on) <TONE> LND

ON-HOOK (LED turns off)

- At Pulse mode after off-hook, LED is off during

pulse dialing. When dialing is followed by the ”*”

or ”TONE” softswitch key depressed, the LED will

light up immediately at the softswitch after pulse

dialing is completed to indicate the signalling

mode change from pulse to tone.

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

the device will be in pulse mode and then LED is

turned off. Redialing from LND memory buffer will

repeat the softswitch, i.e. mixed mode redialing,

the LED will light up to indicate the switch to tone

mode or tone dialing. The LED will turn off only

when the telephone goes on-hook or is reset by

the Flash key

Examples : Pulse mode

a) OFF-HOOK (LED is off) <Pulse> D1, D2

(LED remains off),”*” <Tone> (LED turns on),

D3, D4

ON-HOOK or Flash (LED turns off)

b) OFF-HOOK (LED is off) <Pulse> LND

<Pulse> D1, D2 (LED remains off), ”*” <Tone>

(LED turns on) D3, D4,

ON-HOOK or Flash (LED turns off)

- At Pulse mode, after off-hook, LED is off during

pulse dialing. When switching the Tone/Pulse me-

chanical switch to Tone mode, LED will turn on.

Example : Pulse mode

OFF-HOOK (LED is off) <Pulse> D1, D2 Switch

”Tone/Pulse” mechanical switch to Tone mode

(LED turns on) <Tone> D3, D4,

ON-HOOK (LED turns off)

The function of the LED for Tone mode indicator is

described in the timing waveform in Figures 2, 3, 4

and 5.

Figure 2 : Tone Mode Timing with Lighted Dial LED (Pin 24 to VDD or GND)

* Dial Se que nc e 1

FLAS H 3

ENTE R

ENTER

Keybo ard

1

Inp ut

*

3

Keybo ard

Scan

E NTER

F LAS H

KE YBOARD S CAN

DTMF

Outpu t

(P in 17)

P ULS E

Outpu t

3

Tflas h

3 : Debounce Time

E NTE R

3

3

LE D

ON

OFF

ON

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