Simplified 3-phase mapping and coding

1. A method for data communication, comprising:

configuring a 3-phase encoder for a first mode of operation in which data is encoded in a sequence of two-bit symbols;

transmitting a first three-phase signal that is representative of the sequence of two-bit symbols on each of three wires, wherein the first three-phase signal is in a different phase on each wire when each symbol in the sequence of two-bit symbols is transmitted, and wherein a transition in signaling state in one or more wires occurs between transmission of each pair of symbols in the sequence of two-bit symbols;

configuring the 3-phase encoder for a second mode of operation in which data is encoded in a sequence of three-bit symbols; and

transmitting a second three-phase signal that is representative of the sequence of three-bit symbols on each of the three wires, wherein the second three-phase signal is in a different phase on each wire when each symbol in the sequence of three-bit symbols is transmitted, and wherein a transition in signaling state in at least one wire occurs between transmission of each pair of symbols in the sequence of three-bit symbols.

2. The method of claim 1 , wherein signaling states of the three wires are defined by polarity and direction of rotation when the 3-phase encoder is configured for the first mode of operation.

3. The method of claim 2 , wherein each symbol in the sequence of two-bit symbols selects between four transitions that are available from each signaling state of the three wires when the 3-phase encoder is configured for the first mode of operation.

4. The method of claim 2 , wherein each symbol in the sequence of two-bit symbols comprises a first bit that determines whether a next signaling state has a different polarity than a current signaling state, and a second bit that defines phase rotation associated with the next signaling state.

5. The method of claim 2 , wherein each symbol in the sequence of three-bit symbols selects between five transitions that are available from each signaling state when the 3-phase encoder is configured for the second mode of operation.

6. The method of claim 5 , wherein each symbol in the sequence of three-bit symbols comprises a first bit that determines whether a next signaling state has a different polarity than a current signaling state, a second bit that defines phase rotation associated with the next signaling state, and a third bit that determines whether the next signaling state involves only a polarity switch from the current signaling state.

7. The method of claim 1 , further comprising:

determining presence of a misalignment of the three wires involving two or more wires;

inverting a phase rotation bit of each symbol in the sequence of two-bit symbols when the misalignment of the three wires is determined to affect phase relationships between signals carried on the three wires when the 3-phase encoder is configured for the first mode of operation; and

inverting a phase rotation bit of each symbol in the sequence of three-bit symbols when the misalignment of the three wires is determined to affect phase relationships between signals carried on the three wires when the 3-phase encoder is configured for the second mode of operation.

8. The method of claim 7 , wherein the presence of the misalignment of the three wires is determined during a training transmission.

9. A data communication apparatus, comprising:

a bus interface configured to couple the apparatus to three wires of a communication link;

a 3-phase encoder adapted to provide sequences of symbols used to configure three-phase signals transmitted over the three wires; and

a processing circuit configured to:

configure the 3-phase encoder for a first mode of operation in which data is encoded in a sequence of two-bit symbols;

transmit a first three-phase signal that is representative of the sequence of two-bit symbols on each of the three wires, wherein the first three-phase signal is in a different phase on each wire when each symbol in the sequence of two-bit symbols is transmitted, and wherein a transition in signaling state in one or more wires occurs between transmission of each pair of symbols in the sequence of two-bit symbols;

configure the 3-phase encoder for a second mode of operation in which data is encoded in a sequence of three-bit symbols; and

transmit a second three-phase signal that is representative of the sequence of three-bit symbols on each of the three wires, wherein the second three-phase signal is in a different phase on each wire when each symbol in the sequence of three-bit symbols is transmitted, and wherein a transition in signaling state in at least one wire occurs between transmission of each pair of symbols in the sequence of three-bit symbols.

10. The apparatus of claim 9 , wherein signaling states of the three wires are defined by polarity and direction of rotation when the 3-phase encoder is configured for the first mode of operation.

11. The apparatus of claim 10 , wherein each symbol in the sequence of two-bit symbols selects between four transitions that are available from each signaling state when the 3-phase encoder is configured for the first mode of operation.

12. The apparatus of claim 10 , wherein each symbol in the sequence of two-bit symbols comprises a first bit that determines whether a next signaling state has a different polarity than a current signaling state, and a second bit that defines phase rotation associated with the next signaling state.

13. The apparatus of claim 10 , wherein each symbol in the sequence of three-bit symbols selects between five transitions that are available from each signaling state when the 3-phase encoder is configured for the second mode of operation.

14. The apparatus of claim 13 , wherein each symbol in the sequence of three-bit symbols comprises a first bit that determines whether a next signaling state has a different polarity than a current signaling state, a second bit that defines phase rotation associated with the next signaling state, and a third bit that determines whether the next signaling state involves only a polarity switch from the current signaling state.

15. The apparatus of claim 9 , wherein the processing circuit is further configured to:

determine presence of a misalignment of the three wires involving two or more wires;

invert a phase rotation bit of each symbol in the sequence of two-bit symbols when the misalignment of the three wires is determined to affect phase relationships between signals carried on the three wires when the 3-phase encoder is configured for the first mode of operation; and

invert a phase rotation bit of each symbol in the sequence of three-bit symbols when the misalignment of the three wires is determined to affect phase relationships between signals carried on the three wires when the 3-phase encoder is configured for the second mode of operation.

16. The apparatus of claim 15 , wherein the presence of the misalignment of the three wires is determined during a training transmission.

17. A processor-readable storage medium having one or more instructions which, when executed by at least one processor of a processing circuit, cause the processing circuit to:

configure a 3-phase encoder for a first mode of operation in which data is encoded in a sequence of two-bit symbols;

transmit a first three-phase signal that is representative of the sequence of two-bit symbols on each of three wires, wherein the first three-phase signal is in a different phase on each wire when each symbol in the sequence of two-bit symbols is transmitted, and wherein a transition in signaling state in one or more wires occurs between transmission of each pair of symbols in the sequence of two-bit symbols;

configure the 3-phase encoder for a second mode of operation in which data is encoded in a sequence of three-bit symbols; and

transmit a second three-phase signal that is representative of the sequence of three-bit symbols on each of the three wires, wherein the second three-phase signal is in a different phase on each wire when each symbol in the sequence of three-bit symbols is transmitted, and wherein a transition in signaling state in at least one wire occurs between transmission of each pair of symbols in the sequence of three-bit symbols.

18. The storage medium of claim 17 , wherein signaling states of the three wires are defined by polarity and direction of rotation when the 3-phase encoder is configured for the first mode of operation.

19. The storage medium of claim 18 , wherein each symbol in the sequence of two-bit symbols selects between four transitions that are available from each signaling state of the three wires when the 3-phase encoder is configured for the first mode of operation.

20. The storage medium of claim 18 , wherein each symbol in the sequence of two-bit symbols comprises a first bit that determines whether a next signaling state has a different polarity than a current signaling state, and a second bit defines phase rotation associated with the next signaling state.

21. The storage medium of claim 18 , wherein each symbol in the sequence of three-bit symbols selects between five transitions that are available from each signaling state when the 3-phase encoder is configured for the second mode of operation.

22. The storage medium of claim 21 , wherein each symbol in the sequence of three-bit symbols comprises a first bit that determines whether a next signaling state has a different polarity than a current signaling state, a second bit defines phase rotation associated with the next signaling state, and a third bit that determines whether the next signaling state involves only a polarity switch from the current signaling state.

23. The storage medium of claim 17 , further comprising:

determine presence of a misalignment of the three wires involving two or more wires;

invert a phase rotation bit of each symbol in the sequence of two-bit symbols when the misalignment of the three wires is determined to affect phase relationships between signals carried on the three wires when the 3-phase encoder is configured for the first mode of operation; and

invert a phase rotation bit of each symbol in the sequence of three-bit symbols when the misalignment of the three wires is determined to affect phase relationships between signals carried on the three wires when the 3-phase encoder is configured for the second mode of operation.

24. The storage medium of claim 23 , wherein the presence of the misalignment of the three wires is determined during a training transmission.

25. An apparatus comprising:

means for configuring a 3-phase encoder, wherein in a first mode of operation, data is encoded in a sequence of two-bit symbols, and wherein in a second mode of operation, data is encoded in a sequence of three-bit symbols; and

means for transmitting three-phase signals on each of three wires,

wherein in the first mode of operation, a first three-phase signal that is representative of the sequence of two-bit symbols is transmitted on each of the three wires, wherein the first three-phase signal is in a different phase on each wire when each symbol in the sequence of two-bit symbols is transmitted, and wherein a transition in signaling state in one or more wires occurs between transmission of each pair of symbols in the sequence of two-bit symbols, and

wherein in the second mode of operation, a second three-phase signal that is representative of the sequence of three-bit symbols is transmitted on each of the three wires, wherein the second three-phase signal is in a different phase on each wire when each symbol in the sequence of three-bit symbols is transmitted, and wherein a transition in signaling state in one or more wires occurs between transmission of each pair of symbols in the sequence of three-bit symbols.

26. The apparatus of claim 25 , wherein signaling states of the three wires are defined by polarity and direction of rotation when the 3-phase encoder is configured for the first mode of operation.

27. The apparatus of claim 26 , wherein each symbol in the sequence of two-bit symbols selects between four transitions that are available from each signaling state when the 3-phase encoder is configured for the first mode of operation.

28. The apparatus of claim 26 , wherein each symbol in the sequence of two-bit symbols comprises a first bit that determines whether a next signaling state has a different polarity than a current signaling state, and a second bit defines phase rotation associated with the next signaling state.

29. The apparatus of claim 26 , wherein each symbol in the sequence of three-bit symbols selects between five transitions that are available from each signaling state when the 3-phase encoder is configured for the second mode of operation.

30. The apparatus of claim 29 , wherein each symbol in the sequence of three-bit symbols comprises a first bit that determines whether a next signaling state has a different polarity than a current signaling state, a second bit defines phase rotation associated with the next signaling state, and a third bit that determines whether the next signaling state involves only a polarity switch from the current signaling state.