ST75951 datasheet(11/21 Pages) STMICROELECTRONICS

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FUNCTIONAL DESCRIPTION (continued)

1MHz

RING

BIT &

OUTPUT

1MHz

Figure 15

D5 = D6 = VDD.

7.3 - Caller ID

Depending on Pin HM status (see Table 2), 2 pos-

sibilities are offered to control the device to go in

caller ID state.

F0 clock is send to D5, in caller ID mode the

modulation frequency of ST952 is equal to F0/2, so

the demodulation on the receive signal at D3, D4

is at F0/2 in caller ID mode.

Figure 16

D6 = VDD.

O Output at D5

O/2 Demod

Control Signal

Caller ID Mode Phase Relative Hip

Figure 17

8 - Phone Line Monitoring Features

This chipset is intended to be used for a wide range

of application such as modem, answering machine,

telephony on PC, so because the home PSTN

phone line will be shared by several terminals,

information concerning the line status has to be

sent to the host.

As long as there is an alerting signal at D3, D4 Pins,

the ADC converter is saturated and outputs 7FFF

or 8000 at DOUT Pin.

8.1 - Line In Use Checking

Before going OFF-HOOK the modem software can

check that the line is free by setting the CLID mode

and check that the RING Pin/bit output a low pulse.

When in CLID mode if the line is free the ST952 will

output a F0/2, 5VPP differential signal on D3, D4

(see Figure 18).

8.2 - Digital Phone Line or Over Loop Current

Limit Detect

When portable modem plug into digital line, it will cause

over loop current during modem off-hook state.

The modem controller should know this condition

and go onhook to avoid the DAA being damaged.

ST952 when OFF-HOOK will determine if the loop

current exceeds the current limit or not (160mA).

If we have overcurrent ST952 will continuously

output a low level on RING output Pin.

ST75951

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