Multiplexed digital audio and control/status serial protocol

• US 5,532,556 A
• Filed: 09/28/1994
• Issued: 07/02/1996
• Est. Priority Date: 05/12/1992
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Oxford, William V., Anderson, Eric C., Wilson, David F.
• Primary Examiner(s): Tse, Young T.
• Assistant Examiner(s): LUTHER, WILLIAM A
• Application Number:
  US08/314,538
• Time in Patent Office: 643 Days
• Field of Search: 370/110.1, 370/110.4, 370/111, 370/105.1, 370/105.2, 370/103, 370/85.11, 370/100.1, 370/105.5, 370/101, 370/105.4, 381/2, 381/77, 375/356, 375/238, 375/220, 375/257, 375/368, 369/1, 379/67, 371/37.1, 371/42, 371/47.1
• US Class Current: 375/356
• CPC Class Codes: H04H 60/04 Studio equipment; Interconnection of studios
• CPC Class Codes: H04L 7/0331 with a digital phase-locked loop [PLL] processing binary samples, e.g. add/subtract logic for correction of receiver clock H04L7/0337 takes precedence

Abstract

A protocol for transferring audio data and control/status data between audio functional units. The protocol involves multiplexing the audio data and control/status data. The multiplexed data is then transferred between a first audio unit and a second audio unit on two wires, each corresponding to the direction of data flow, and according to a clock rate and a synchronization pattern on third and fourth wires respectively.

Claims

1. A method for transferring audio and auxiliary data between a first audio functional unit and a plurality of second audio functional units using a plurality of conductors, wherein said auxiliary data is capable of including control and status information, said method comprising the steps of:

said first audio functional unit generating a clock signal on a first of the plurality of conductors and generating a synchronization signal having variable length synchronization pulses on a second of the plurality of conductors that identifies each of a plurality of frames and each of a plurality of subframes contained therein;

said first audio functional unit combining audio data with auxiliary data having control information for controlling the plurality of second audio functional units to produce first combined data;

said first audio functional unit transferring said first combined data on a third of said plurality of conductors to the plurality of second audio functional units to control functionality of the plurality of second audio functional units and to request status information from the plurality of second audio functional units, such that the first audio functional unit exerts control on the plurality of second audio functional units;

each of said plurality of second audio functional units receiving a distinct portion of said first combined data only during separate and distinct subframes in each of the plurality of subframes to which said each second audio functional unit is tuned, wherein said step of receiving comprises the steps of

said each of said plurality of second audio functional units identifying said plurality of frames and said separate and distinct subframes according to synchronization pulses of the synchronization signal on the second conductor, and

each of said plurality of second audio functional units tri-stating inputs during subframes other than one of said separate and distinct subframes to which said each second audio functional unit is tuned in each of the plurality of frames;

said plurality of second audio functional units combining audio data with auxiliary data having status information to produce second combined data; and

said each of said plurality of second audio functional units transferring said second combined data on a fourth of said plurality of conductors to the first audio functional unit to supply status information regarding the plurality of second audio functional units only during said separate and distinct subframes in each of the plurality of subframes to which said each of said plurality of second audio functional units is tuned and in response to a status request on said third of said plurality of conductors wherein said step of said each of said plurality of second audio functional units transferring said second combined data on a fourth of said plurality of conductors further comprises the steps of

said each of said plurality of second audio functional units identifying said plurality of frames and said separate and distinct subframes according to synchronization pulses of the synchronization signal on the second conductor, and

said each of sold plurality of second audio functional units tri-stating outputs during subframes other than one of said separate and distinct subframes to which said each second audio functional unit is tuned in each of the plurality of frames.

2. The method as defined in claim 1 wherein said steps of combining comprise multiplexing said audio data with said auxiliary data.

3. The method as defined in claim 2 wherein said steps of multiplexing includes the step of formatting said audio data and said auxiliary data into said one of the plurality of subframes, wherein each of said plurality of subframes comprises a pair of audio channels.

4. The method as defined in claim 3 wherein said steps of formatting comprises arranging said audio data and said auxiliary data within each of said plurality of subframes into a left and a right audio channel.

5. The method as defined in claim 1 further comprising the step of separating the audio data and auxiliary data.

6. An audio system comprising:

a first audio functional unit;

a second audio functional unit; and

an interface coupled between the first audio functional unit and the second audio functional unit, wherein the interface comprises a first conductor, a second conductor, a third conductor and a fourth conductor, wherein the first conductor transfers combined audio and auxiliary data from the first audio functional unit to the second audio functional unit and the second conductor transfers combined audio and auxiliary data from the second audio functional unit to the first audio functional unit, and further wherein transfers between the first audio functional unit and the second audio functional unit occur according to a clock on the third conductor that is generated by the first audio functional unit and according to a synchronization signal on the fourth conductor;

wherein auxiliary data transferred on the first conductor controls functionality of the second audio functional unit and requests status information from the second audio functional unit, such that first audio functional unit exerts control over functionality of the second audio functional unit, and further wherein auxiliary data transferred on the second conductor provides status information regarding the second audio functional unit in response to status information requests from the first audio functional unit, such that the first audio functional unit accesses status information from the second audio functional unit

and further wherein data is transferred in a plurality of frames comprising a plurality of subframes, said second audio functional unit being tuned to one of the plurality of subframes in each of the plurality of frames, such that said second audio functional unit receives data from and transfers data to the first audio functional unit only during a subframe associated with said second audio functional unit, said second audio functional unit disabling its outputs and inputs during subframes other than the subframe associated with said second audio functional unit, and

wherein a variable length synchronization pulse on the fourth conductor indicates a start of each frame and each of the plurality of subframes to enable the first audio functional unit and the second audio functional unit to identify the subframe associated with said second audio functional unit.

7. The system defined in claim 6 wherein said second audio functional unit tri-states the outputs and inputs during subframes other than the subframe associated with said second audio functional unit.

8. A system comprising:

a first unit;

a plurality of audio functional units;

an interface connecting the first unit to the plurality of audio functional units, wherein the interface comprises a first conductor, a second conductor, a third conductor and a fourth conductor, wherein the first conductor transfers combined audio and auxiliary data from the first unit to the plurality of audio functional units and the second conductor transfers combined audio and auxiliary data from the plurality of audio functional units to the first unit, and wherein data transfers occur according to a clock signal on the third conductor generated by the first unit;

and further wherein data is transferred in frames comprising a plurality of subframes, each of said plurality of audio functional units tuned to one of the plurality of subframes, such that data transfers between the first unit and each of a plurality of audio functional units are made using the subframe associated with each audio functional unit, wherein inputs and outputs of each of said plurality of audio functional units are tri-stated during all other subframes, and

wherein variable length synchronization pulses on the fourth conductor indicate a start of each frame and each of the plurality of subframes to enable the first unit and the plurality of audio functional units to identify the subframe associated with said each audio functional unit.

9. The system defined in claim 8 wherein the start of each frame is indicated to the plurality of audio functional units by one of the variable length synchronization pulse having a first length.

10. The system defined in claim 9 wherein a start of each subframe is indicated by one of the variable length synchronization pulse having a second length different from the first length.

11. The system defined in claim 10 wherein said one of the synchronization pulse having the second length comprises a word sync pulse.