si2439-a-gm Silicon Laboratories, si2439-a-gm Datasheet - Page 23

• Manufacturer Part Number: si2439-a-gm
• Description: V.92 And V.34 Isomodem With Global Daa
• Manufacturer: Silicon Laboratories

4.15. Caller ID Operation
The Si2494/39 supports full type I and type II caller ID detection and decode. Caller ID is supported for the US
Bellcore, European ETSI, UK, and Japanese protocols and is enabled via the +VCID, +VCDT, and +PCW
commands.
4.16. Parallel Phone Detection
The ISOmodem
allows the host to avoid interrupting another phone call when the phone line is already in use and to intelligently
handle an interruption when the ISOmodem is using the phone line.
4.16.1. On-Hook Line-in-use Detection
When the ISOmodem is sharing the telephone line with other devices, it is important that it not interrupt a call in
progress. To detect whether another device is using the shared telephone line, the host can use the ISOmodem to
monitor the TIP-RING dc voltage with the line voltage sense (LVS) register (U6C, bits 15:8). The LVS bits have a
resolution of 1 V per bit with an accuracy of approximately ±10%. Bits 0 through 6 of this 8-bit signed twos
complement number indicate the value of the line voltage, and the sign bit (bit 7) indicates the polarity of TIP and
RING. The ISOmodem can also monitor the TIP-RING dc voltage using the LVCS register (U79, bits 4:0). See
Figure 8 on page 23. See also the %Vn commands for automatic line-in-use detection.
4.16.2. Off-Hook Intrusion Detection
When the ISOmodem is off-hook, an algorithm is implemented in the ISOmodem to automatically monitor the TIP-
RING loop current via the LVCS register. During the off-hook state, the LVCS register switches from representing
the TIP-RING voltage to representing the TIP-RING current. See Figure 9 on page 24. Upon detecting an intrusion,
the ISOmodem alerts the host of the condition via the INT pin.
LVC S
BITS
30
25
20
15
10
®
5
0
is able to detect when another telephone, modem, or other device is using the phone line. This
0 3 6
9 12 15 18 21 24 28 30 33 36 39 42 45 47 51 54 57 60 63 66 69 72
Figure 8. Loop Voltage
Rev. 1.0
Loop Voltage (V)
75 78 81 84 87
Si2494/39
100
23