Apparatus and method for digital communications with improved delimiter detection

A node circuit for connection to a transmission medium and being operative to couple Manchester encoded data between the transmission medium and an associated consumer device, wherein said Manchester encoded data is sent through the transmission medium in a message frame;

• the node circuit comprising:
• a first detector that detects a preamble of a message frame in which the preamble has a plurality of alternating high and low signal level pulses;
• a second detector that detects a start delimiter of the message frame in which the start delimiter has a specified pattern of a plurality of binary signal levels which satisfies the following criteria:
• (1) the start delimiter begins with a binary signal level that is opposite to a last binary signal level of the preamble,
• (2) the start delimiter ends with two different binary signal levels,
• (3) a maximum number of consecutive identical binary signal levels is two,
• (4) a digital sum variance which falls in a range of -1 to 2,
• (5) assuming proper synchronization of signal decoding, at least four binary signal levels must be in error in order for random valid data to alias into the specified pattern of said start delimiter,
• (6) assuming improper synchronization of signal decoding, at least two binary signal levels must be in error in order for random valid data to alias into the specified pattern of said start delimiter;
• a data decoder which is responsive to said a second detector detecting a start delimiter by decoding data in the message frame;
• and
• a signal path to carry decoded data from said data decoder to the associated consumer device.

A method of transmitting a digital data over a communication network from an originating node to a recipient node using Manchester data encoding in which the digital data is sent as a series of binary signal levels, said method comprising steps of:

• transmitting a preamble having a defined pattern of alternating high and low logic level pulses of substantially equal duration;
• transmitting a start delimiter that contains violations of Manchester data encoding and which satisfies the following criteria:
• (a) the start delimiter begins with a binary signal level that is opposite to a last binary signal level of the preamble,
• (b) the start delimiter ends with a pair of different binary signal levels,
• (c) a maximum number of consecutive symbol periods having identical binary signal levels is two,
• (d) a digital sum variance of the start delimiter falls in a range -1 to 2,
• (e) assuming proper synchronization of signal decoding, at least four binary signal levels must be in error in order for random valid data to alias into the start delimiter pattern, and
• (f) assuming improper synchronization of signal decoding, at least two binary signal levels must be in error in order for random valid data to alias into the start delimiter pattern;
• transmitting the digital data;
• transmitting a cyclic redundancy code that was derived from the digital data;
• and
• transmitting an end delimiter.