SI2414 SILABS [Silicon Laboratories], SI2414 Datasheet - Page 35

• Manufacturer Part Number: SI2414
• Manufacturer: SILABS [Silicon Laboratories]

Data Compression
The modem can achieve DTE (host-to-ISOmodem)
speeds greater than the maximum DCE (modem-to-
modem) speed through the use of a data compression
protocol. The compression protocols available are the
ITU-T V.42bis and MNP5 protocols. Data compression
attempts to increase throughput by compressing the
information to be sent before actually sending it. The
modem is, thus, able to transmit more data in a given
period of time. Table 17 details the Si2456/33/14 error
correction and data compression modes of operation.
Error Correction
The Si2456/33/14 ISOmodem can employ error
correction (reliable) protocols to ensure error-free
delivery of asynchronous data sent between the host
and the remote end. The error control methods are
based on grouping data into frames with checksums
determined by the contents of each frame. The
receiving modem checks the frames and sends
acknowledgments to the transmitting modem. When it
detects a faulty frame, the receiving modem requests a
retransmission. Frame length varies according to the
amount of data transmitted or the number of
retransmissions requested from the opposite end.
The Si2456/33/14 supports V.42 and MNP2-4 error
correction protocols. V.42 (LAPM) is most commonly
used and is enabled in \N3 and \N4 modes. In the
default mode (\N3), the Si2456/33/14 attempts to
connect with V.42 error correction and V.42bis data
compression and falls back to either V.42 only or no
error correction (wire mode) if necessary. In \N4 mode,
the Si2456/33/14 hangs up if a V.42 connection cannot
be established. If the ISOmodem hangs up in V.42
mode after all data is successfully sent, the result code
is “OK”. If the modem hangs up before all data is
successfully sent, the result code is “No Carrier”. The
“No Carrier” result code will also be given in the \N4
V.42 (LAPM)
V.42bis
Wire
V.42 and
V.42bis only
V.42 only
MNP2-4 only
MNP2-5 only
No data compression and
no error correction
Table 17. Enabling Error Correction/Data
To Enable
Compression
\N3 and %C1 (default)
Use AT Commands
\N4 and %C1
\N4 and %C0
\N2 and %C1
\N0 and %C0
\N2
Rev. 0.9
mode if V.42 negotiation is unsuccessful.
The V.42 specification allows an alternate error
correction protocol, MNP2-4. MNP2-4 is enabled in \N2
mode. In \N2 mode, the Si2456/33/14 hangs up if an
MNP2, 3, or 4 connection cannot be established.
Wire Mode
Wire mode (\N0) is used to communicate with standard
non-error correcting modems. When optioned with \N3,
the Si2456/33/14 falls back to wire mode if it fails in an
attempt to negotiate a V.42 link with the remote modem.
Error correction and data compression are not active in
wire mode.
Caller ID Operation
The Si2456/33/14 supports full caller ID detection and
decode for the US Bellcore and European ETSI
protocols.
The Si2456/33/14 detects the first ring burst signal and
echoes “RING” to the host. The device starts searching
for the caller ID preamble sequence after the
appropriate time-out. When 50 continuous mark bits
have been detected, the “CIDM” response is echoed to
indicate that the mark has been detected and that caller
ID data follows. If enabled (via the +VCID and +VCDT
AT commands), the INT pin goes active.
At this point, the algorithm looks for the first start bit,
assemble the characters, and transmits them to the host
as they are detected. When the caller ID burst finishes,
the carrier is lost, and the modem echoes a “NO
CARRIER” to indicate that the carrier is lost.
At this point, the Si2456/33/14 continues detecting ring
bursts and echoing “RING” for each burst and answers
automatically after the correct number of rings.
UK Caller ID Operation
When the Si2456/33/14 detects a line reversal, it
echoes a “FLASH” to the host, and, if enabled, the INT
pin activates.
The ISOmodem begins searching for the Idle State Tone
Alert Signal. When this signal has been detected, it
echoes “STAS” to the host. After the Idle State Tone
Alert Signal is completed, the ISOmodem applies the
wetting pulse for the required 15 ms by quickly going
off-hook and on-hook. From this point on, the algorithm
is identical to that of Bellcore in that it searches for the
channel seizure signal and the marks before echoing
“CIDM” and reports the decoded caller ID data.
Japan Caller ID Operation
After a polarity reversal and the first ring burst are
detected, the Si2456/33/14 is taken off-hook, and, if
Si2456/Si2433/Si2414
35