SI2493-C-FS Silicon Laboratories Inc, SI2493-C-FS Datasheet - Page 127

• 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

3.5.16. HDLC Example: Bit Errors on a Noisy Line
Bit errors can occur on an impaired line. The problem lies in determining and ignoring the spurious data resulting
from poor line conditions and recovering valid data. This example illustrates a typical data corruption problem due
to a noisy line and the method used to analyze it.
For this example, the modem is a Si2404 configured with the following initialization string after reset.
AT+ES=6,,8
AT+ESA=0,0,0,,1,0
AT+ITF=0383,0128
AT:U87,010A
AT+MS=V22
AT:U7A,3
The following data stream was received over a noisy line.
0D 0A 43 4F 4E 4E 45 43 54 20 31 32 30 30 0D 0A 19 BE 20 20 19 B1 19 B0 19 B2 30 93
19 B1 19 B2 30 93 19 B1 19 B2 30 93 19 B1 19 B2 30 93 19 B1 19 B2 19 B2 B6 9E F7 46
19 B0 19 B2 29 C6 19 B0 19 B2 FF 98 89 18 19 B0 19 B2 92 6E EF 14 65 19 B0 19 B2 DA
BE C6 07 EA D8 31 C2 05 3C FA C8 86 C4 40 E6 19 A0 CA EA A8 F9 19 B2 8D 00 57 A5 43
29 19 B0 19 B2 05 CB 14 9F 7C 2D 19 B0 19 B2 19 B2 19 BA 0D 0A 4E 4F 20 43 41 52 52
49 45 52 0D 0A
First, the data will be analyzed to point out the occurrence of bit errors and spurious data. Secondly, a simple
algorithm to filter the data will be proposed. Finally, the resulting valid data will be presented.
Table 86 lists an initial analysis of some recurring data patterns.
0D 0A 43 4F 4E 4E 45 43 54 20 31 32 30 30
0D 0A
19 BE 20 20
19 B0
19 B2
19 B1
Data
Table 86. Bit Errors
Rev. 0.9
Is an indication the modem has detected a pattern with >
6 marks in a row. Once this occurs, the receiver begins
looking for HDLC flags. Until the occurrence of HDLC
flags, 19 B2 and subsequent data is discarded.
This pattern has three meanings.
The data can be analyzed as follows with valid data
shown in bold.
Received first flag.
If the receiver is looking for HDLC flags, 19B2 means
that the receiver has found an HDLC flag.
If 19B2 is received after a packet has started (prior
data exists), the receiver assumes the CRC check
does not match the FCS bytes sent by the remote
transmitter and declares the packet bad.
An isolated 19 B2 pattern (no preceding data) is
normal. This can occur when the following example
data pattern is seen: 7E 7E XX 7E 7E (where XX can
be up to 2 bytes of non-FLAG bit patterns at the
DCE).
CONNECT 1200
tx 1200 rx 1200
Meaning
AN93
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