SI2493-C-FS Silicon Laboratories Inc, SI2493-C-FS Datasheet - Page 123

• Manufacturer Part Number: SI2493-C-FS
• Description: IC ISOMODEM SYSTEM-SIDE 16SOIC
• Manufacturer: Silicon Laboratories Inc

Specifications of SI2493-C-FS

• Mfg Application Notes: SI2493/57/34/15/04, Appl Note AN93
• Data Format: V.21, V.22, V.23, V.29, V.32, V.34, V.90, V.92, Bell 103, Bell 212A
• Baud Rates: 56k
• Interface: UART
• Voltage - Supply: 3 V ~ 3.6 V
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

3.5.5. Intrusion/Parallel Phone Detection
The modem may share a telephone line with a variety of
other devices, particularly telephones. In most cases,
the modem has a lower priority for access to the phone
line. Someone dialing 911 in an emergency, for
example, has a higher priority than a set-top box
updating billing information. If someone is using a
telephone, the modem should not go off-hook. If
someone picks up a phone while the modem is
connected or dialing, the modem should drop the
connection and allow the phone call to proceed. The
modem must monitor the phone line for intrusion in both
the on-hook and off-hook conditions.
3.5.6. Intrusion Detection—On-Hook Condition
When the ISOmodem is on-hook, the U79[4:0] (LVCS)
value represents TIP-RING voltage; the ISOmodem is
in the command mode, and the host can easily monitor
LVCS with the AT:R79 command. A typical local loop
has a TIP-to-RING voltage greater than 40 V if all
devices sharing the loop (telephones, FAX machines,
modems, etc.) are on-hook. The typical local loop has a
large dc impedance that causes the TIP-RING voltage
to drop below 25 V when a device goes off-hook. The
host can monitor LVCS to determine whether the TIP-
RING voltage is approximately 40 V or something less
than 25 V to determine if a parallel device is off-hook.
This type of monitoring may also be performed with the
%V1 command. Alternatively, the host could be
programmed to periodically monitor LVCS and store the
maximum value as the “all devices on-hook” line voltage
and establish the on-hook intrusion threshold as a
fraction (possibly 50%) of that value. This allows the
system to adapt to different or changing local loop
conditions. An on-chip adaptive monitoring algorithm
may be enabled with the %V2 command.
3.5.7. Line Not Present/in Use Indication
If enabled with %V1, this feature checks the line status
before going off-hook and again before dialing. Before
going off-hook with the ATD, ATO, or ATA command, the
Si2493/57/34/15/04
compares it to U83 (NOLN)[15:0] and U84 (LIUS)[15:0].
Example
(Method 1 - Fixed)
reads
the
line
voltage
and
Rev. 0.9
A debounce timer controlled by U-registers 50 and 51
prevents polarity reversals from being detected as a
loss of loop current. The intrusion detection algorithm
continues to operate if U77(HOI)[11] is set. In this case,
a parallel phone intrusion while off-hook gives a “LINE
IN USE” result code to indicate the Si2493/57/34/15/04
has gone on-hook due to a parallel phone intrusion.
Note: This method may not be as desireable as method 2,
Pros:
Cons:
3.5.8. Line Not Present/In Use Indication
This method is enabled through %V2. This feature
checks the line status before going off-hook and again
before dialing. While on-hook, the part monitors line
voltage and updates U85(NLIU)[15:0] with this value.
Before going off-hook with the ATD, ATO, or ATA
command, the Si2493/57/34/15/04 reads the line
voltage and compares it with the stored reference.
0 < LVCS < U83
U83 < LVCS < U84
(U-register)
U84 < LVCS
0 < LVCS < 6.25% x U85
6.25% U85. < LVCS < 85% x
U85
85% U85. < LVCS
Loop voltage
Easy to understand and predict
Allows reference level control
Chosen levels must work for all lines—Not adaptive
(Method 2—Adaptive)
particularly for low-voltage lines.
Loop Voltage
Report “NO LINE” remain on-hook
Report “LINE IN USE” remain on-
hook
Go off-hook and establish connec-
tion
Report “NO LINE”
remain on-hook
Report “LINE IN
USE” remain on-hook
Go off-hook and
establish connection
Action
Action
AN93
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