Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 166)

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166 Rev. 1.3
Table 104. Bit Errors
Data Meaning
19 B0 Is an indication the modem has detected a pattern with
more than 6 marks in a row. Once this occurs, the
receiver begins looking for HDLC flags. Until the occur-
rence of HDLC flags, 19 B2 and subsequent data are
discarded.
19 B2
This pattern has three meanings.
 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).
The data can be analyzed as follows with valid data
shown in bold.
0D 0A 43 4F 4E 4E 45 43 54 20 31 32 30 30
0D 0A
CONNECT 1200
19 BE 20 20 tx 1200 rx 1200
19 B1 Received first flag.
Beginning of Packet
19 B0 A spurious byte received with more than 6 mark bits in a
row. The modem is looking for HDLC flags.
19 B2 HDLC flag detected.
Beginning of Packet
30 93
19 B1
Good Packet.
Beginning of Packet
19 B2 If a 1-bit error is received in an HDLC flag, the modem
assumes a new single-byte packet. Since a 1-byte
packet is invalid, 19 B2 is generated by modem.
Beginning of Packet
30 93
19 B1
Good Packet
Beginning of Packet