Self-clocked data transmission system having automatic signal reversing means

• US 4,216,426 A
• Filed: 06/05/1979
• Issued: 08/05/1980
• Est. Priority Date: 03/02/1979
• Status: Expired due to Term

• Current Assignee: Unisys Corporation
• Original Assignee: Burroughs Incorporated (Terreno Realty Corp.)
• Inventors: Flora, Laurence P.
• Primary Examiner(s): Pitts, Harold I.
• Application Number:
  US06/045,806
• Time in Patent Office: 427 Days
• Field of Search: 325/38 A, 340/347 DD, 178/53.1, 178/69 D
• US Class Current: 375/292
• CPC Class Codes: H04L 25/4925 using balanced bipolar ternary codes

Abstract

A two-wire digital data transmission system wherein pairs of binary input signals are encoded into a self-clocked three-level signal. Predetermined start bits and a valid signal are employed in a manner which permits signal reversing to automatically occur at the receiving end so as to provide proper polarity for the received signal.

Claims

1. In a digital data transmission system, the improvement comprising:

encoding means responsive to an applied clock signal and to an applied valid signal for encoding input binary signals into a three-level signal having first and second levels and an intermediate level with level transitions occurring at times determined by said clock signal and with encoding being performed in response to the presence of said valid signal;

said encoding means including means responsive to said valid signal for inserting a predetermined start signal at the beginning of the three-level signal provided in response to input binary signals applied along with a valid signal;

a two-wire transmission line;

driving means for coupling said three-level signal to one end of said transmission line for transmission thereby;

receiving and decoding means coupled to the other end of said transmission line for receiving the transmitted three-level signal, deriving said clock and valid signals therefrom, and employing the derived clock signal for decoding the received three-level signal into binary form;

said receiving and decoding means including signal reversing means responsive to the derived valid signal and start signal occurring at the beginning of a received three-level signal for automatically reversing the three-level signals received from said two-wire transmission line.

2. The invention in accordance with claim 1, wherein said encoding means is operable to encode pairs of input binary signals into corresponding pairs of sequential levels, and wherein said start signal comprises a first level followed by a second level.

3. The invention in accordance with claim 2, wherein signal reversing mans provides one polarity when said start signal is received with said first level followed by said second level and provides a reversed polarity when said start signal is received with said second level followed by said first level.

4. The invention in accordance with claim 1, 2 or 3, wherein said encoding means is operable to encode pairs of input binary signals into corresponding encoded pairs of sequential levels in a manner such that at least one encoded input pair is selectably encodable into either a first pair of sequential levels having a positive average value relative to said intermediate level or into a second pair of sequential levels having a negative average value relative to said intermediate level, said encoding means being operable to select said first or second pair in a manner so as to seek a predetermined average level for the encoded three-level signal relative to said intermediate level.

5. The invention in accordance with claim 4, wherein said first and second levels are equal and of opposite polarity relative to said intermediate level.

6. The invention in accordance with claim 5, wherein said intermediate average level is substantially zero.

7. The invention in accordance with claim 4, wherein said three-level signal is comprised of a high level H, a low level L and an intermediate level I, and wherein said encoding means is operable to encode an input pair into a pair of encoded levels as follows:

space="preserve" listing-type="tabular">______________________________________ INPUT PAIR ENCODED PAIR ______________________________________ 00 IH or IL 01 LH 10 HL 11 HI or LI ______________________________________

8. The invention in accordance with claim 7, wherein said encoding means selects between the encoded pair IH and IL for a 00 input pair and between the encoded pair HI and LI for a 11 input pair in response to detecting the accumulated average level of the encoded three-level signal.

9. The invention in accordance with claim 4, wherein said encoding means operates in response to an input pair designatable as AB to produce an encoded pair designatable as FS in accordance with the following Boolean equations:

space="preserve" listing-type="equation">F.sub.H =A·

B+A·

M

space="preserve" listing-type="equation">F.sub.L =A·

B+B·

M

space="preserve" listing-type="equation">S.sub.H =A·

B+A·

M

space="preserve" listing-type="equation">S.sub.L =A·

B+B·

M

wherein M is true when the encoded signal has an average level which is between L and I;

wherein the F_H and F_S equations set forth the relationships which determine whether the first encoded level F of an encoded pair will have an H or L level, and wherein the S_H and S_L equations set forth the relationships which determine whether the second encoded level S of a transmitted pair will have an H or L level, an I encoded level being produced when the respective equations above are inapplicable.