ST75951 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'ST75951' PDF : 21 Pages View PDF
ST75951
FUNCTIONAL DESCRIPTION (continued)
Figure 15
VCM
D3
1MHz
VCM
D4
1MHz
RING
BIT &
OUTPUT
D5
D6
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
D5
VDD
F0
D6
D6 = VDD.
Figure 17
FO Output at D5
FO/2 Demod
Control Signal
Caller ID Mode Phase Relative Hip
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.
11/21
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