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178
Rev. 1.4
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 118 lists an initial analysis of some recurring data patterns.
Table 118. 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
Содержание Si2404
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Страница 27: ...AN93 Rev 1 4 27 Figure 7 Parallel Interface Read Timing Figure 8 Parallel Interface Write Timing ...
Страница 200: ...AN93 200 Rev 1 4 Figure 31 TAM Handset and Speakerphone Voice Paths ...
Страница 201: ...AN93 Rev 1 4 201 Figure 32 Si3000 Codec Gain and Signal Selection Options ...
Страница 290: ...AN93 290 Rev 1 4 Figure 57 256 Band Spectral Display Figure 58 2048 Band Spectral Display ...
Страница 305: ...AN93 Rev 1 4 305 Figure 76 Parallel or SPI Port Interrupt Service Flowchart ...