Method of encoding data for serial transmission

• US 4,599,723 A
• Filed: 02/14/1984
• Issued: 07/08/1986
• Est. Priority Date: 02/14/1984
• Status: Expired due to Fees

• Current Assignee: Westinghouse Air Brake Co (Westinghouse Air Brake Technologies Corporation)
• Original Assignee: Pulse Electronics Incorporated (Yageo Corporation)
• Inventors: Eck, Henry H.
• Primary Examiner(s): Atkinson, Charles E.
• Application Number:
  US06/580,172
• Time in Patent Office: 875 Days
• Field of Search: 371/70, 371/47, 360/40, 360/47, 360/53, 375/114, 375/116
• US Class Current: 714/798
• CPC Class Codes: H04L 1/08 by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence
• CPC Class Codes: H04L 25/068 by sampling faster than the nominal bit rate
• CPC Class Codes: H04L 7/0066 detection of error based on transmission code rule

Abstract

A technique for redundantly encoding data for synchronous or asynchronous serial transmission or recording and the correlative technique for decoding the serial bit stream are disclosed. The encoding technique involves making the second data string of a data string pair the complement of the first data string and formatting to the format H₁ Data H₂ Data where H₁ and H₂ are headers wherein at least one bit is the same in corresponding bit positions of the headers. Decoding involves first detecting the headers and then checking to confirm that the data fields are complements. Also disclosed is a technique for extracting bits from the data stream.

Claims

1. A method of encoding data for serial transmission or recording comprising the steps of

accepting a data string composed of binary "1'"'"'s" and "0'"'"'s" for transmission or recording,

complementing said data string,

providing each of said data string and its complement with a header, wherein at least one bit is the same in corresponding bit positions of the headers, said headers being used to identify and synchronize transmitted or recorded data by comparing said corresponding bit positions in the headers, and

framing the data to be transmitted or recorded by ordering said data string with its header and the complement of said data string with its header in series.

2. The method according to claim 1 wherein the two headers have at least two bits, at least one bit being the same and at least one bit being different in corresponding bit positions of the headers.

3. A method of decoding a serial bit stram encoded to the format H₁ Data H₂ Data where H₁ and H₂ are headers wherein at least one bit is the same in corresponding bit positions of the headers and Data is a data string and Data is its complement, said method comprising the steps of

shifting said serial bit stram into a buffer,

checking the bits in the buffer to detect the presence of the headers H₁ and H₂ and synchronize the data string by detecting the presence of identical bits in said corresponding bit positions of the headers,

if the headers H₁ and H₂ are detected, checking the data fields to confirm that the data strings are complements, and

if the data fields are complements, providing an indication that data is available, otherwise resume shifting said serial bit stram into the buffer and checking for the presence of the headers H₁ and H₂.

4. The method according to claim 3 wherein the two headers have at least two bits, at least one bit being the same and at least one bit being different in corresponding bit positions of the headers.

5. The method according to claim 3 further comprising extracting the bits individually from the serial bit stream prior to shifting into the buffer, the step of extracting comprising the steps of

sampling the bit stream at a rate n times the bit rate, where n is a positive integer,

framing sequences of n samples, ensuring that the center samples correspond to the center of the transmitted bit,

using all or part of the samples to determine if the bit is a "1" or a "0", and

sending the bit to the buffer.

6. The method according to claim 5 wherein n=1 and the serial bit stream is accompanied by a synchronous clock, said clock being used to sample the bit stream at or near the center of a bit time.

7. The method according to claim 5 wherein n>

1, said method further comprising the steps of

detecting transitions in previous frames, and

moving the current frame forward or backward in the series of samples if the transitions occur near the center of the frame.

8. The method according to claim 7 wherein n=8 and the frame is moved backward if a transition occurs between the fifth and seventh samples, and the frame is moved forward if a transition occurs between the second and fourth samples.

9. The method according to claim 7 wherein the step of moving produces a forward or backward movement of more than a single sample.

10. The method according to claim 7 wherein the bit stream is sampled at a rate greater than n times the bit rate and the step of moving is made only in the backward direction.

11. The method according to claim 7 wherein the bit stream is sampled at a rate less than n times the bit rate and the step of moving is made only in the forward direction.

12. The method according to claim 5 wherein the determination as to whether a bit is a binary "1" or "0" is made by majority vote.

13. The method according to claim 5 further comprising the steps of

detecting bit transitions, and

increasing or decreasing the time between samples of at least a limited number of subsequent samples if the bit transitions occur near the center of the frame.

14. The method according to claim 13 wherein the step of increasing or decreasing the time between samples is performed for all subsequent samples.

15. A method of transmitting and receiving a serial data stream comprising the steps of

accepting a data string composed of binary "1'"'"'s" and "0'"'"'s" for transmission,

complementing said data string,

providing each of said data string and its complement with a header, wherein at least one bit is the same in corresponding bit positions of the headers,

framing the data to be transmitted by ordering said data string with its header and the complement of said data string with its header in series,

serially transmitting the framed data to a receiver,

receiving the transmitted data at said receiver,

shifting the received data into a buffer,

checking the bits in the buffer to detect the presence of the headers by detecting the presence of identical bits in said corresponding bit positions of the headers,

if the headers are detected, synchronizing the receiver with the received data and checking the received data to confirm that the data strings are complements, and

if the data strings are complements, providing an indication that data is available, otherwise resume shifting received data into the buffer and checking for the presence of the headers.

16. The method according to claim 15 wherein the two headers have at least two bits, at least one bit being the same and at least one bit being different in corresponding bit postions of the headers.