Silicon Laboratories SI2493/57/34/15/04, SI2494/39 manual Bit Errors, Dce, Beginning of Packet

AN93

		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			CONNECT 1200
0D	0A
	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	Good Packet.
	19	B1
		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	Good Packet
	19	B1

Beginning of Packet

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