Data transfer
This application relates to methods and apparatus for transfer of multiple digital data streams, especially of digital audio data over a single communications link such as a single wire. The application describes audio interface circuitry comprising a pulse-length-modulation (PLM) modulator ( 204 ). The PLM is responsive to a plurality of data streams (PDM-R, PDM-L), to generate a series of data pulses (PLM) with a single data pulse having a rising and falling edge in each of a plurality of transfer periods defined by a first clock signal (TCLK). The timing of the rising and falling edge of each data pulse is dependent upon on a combination of the then current data samples from the plurality of data streams. The duration and position of the data pulse in the transfer window in effect defines a data symbol encoding the data. Circuitry for receiving and extracting the data is also disclosed. An interface receives the stream of data pulses (PLM) and data extraction circuitry ( 202 ) samples the data pulse to determine which of the possible data symbols the pulse represents and determines a data value for at least one received data stream.
1. An audio accessory apparatus for playback of audio signals received, in use, from an electronic device comprising:
at least first and second audio output transducers;
a connector for removably connecting the audio accessory apparatus to the electronic device in use, the connector having a plurality of contacts; and
interface circuitry for receiving said audio signals via said connector, the interface circuitry comprising a digital module for receiving digital audio signals via said connector and driving said audio output transducers based on said received digital audio signals;
wherein the interface circuitry is operable:
in a first mode to connect first and second contacts of said plurality of contacts directly to the first and second audio output transducers respectively to drive said audio output transducers with analogue audio signals received at said first and second contacts; and
in a second mode to disconnect the first and second contacts of the plurality of contacts from the first and second audio output transducers respectively and to provide at least a first digital signal path from the first contact to the digital module;
wherein, in the second mode of operation, the interface circuitry is configured to derive power for said digital module from at least one power supplying contact of said plurality of contacts of said connector; and
wherein the interface circuitry comprises discrimination circuitry configured to, when power is available via the at least one power supplying contact, determine whether to operate in the second mode and, if so, generate a control signal to disable the analogue signal paths.
2. An audio accessory apparatus as claimed in claim 1 comprising first and second switches for enabling/disabling the first and second analogue signal paths respectively wherein the first and second switches default to enabling the first and second analogue signal paths.
3. An audio accessory apparatus as claimed in claim 1 wherein, in the second mode of operation, the interface circuitry is configured to derive power for said digital module from at least one power supplying contact of said plurality of contacts of said connector.
4. An audio accessory apparatus as claimed in claim 3 wherein said at least one power supplying contact comprises at least one of the first and second contacts.
5. An audio accessory apparatus as claimed in claim 3 wherein, in the second mode of operation, one of said at least one power supplying contacts is used to receive a digital audio signal and the interface comprises a power harvesting module for deriving power from the received digital audio signal.
6. An audio accessory apparatus as claimed in claim 1 wherein said discrimination circuitry is configured to, when power is available via the at least one power supplying contact, to attempt handshaking with a device connected via said connector.
7. An audio accessory apparatus as claimed in claim 1 further comprising a first microphone, wherein said connector comprises a third contact and the interface circuitry is operable in the first mode to provide a third analogue signal path for providing a microphone bias from the third contact to the first microphone.
8. An audio accessory apparatus as claimed in claim 7 wherein the interface circuitry is operable in the second mode of operation to operate the microphone and derive a digital microphone signal and to transmit the digital microphone signal to the connected electronic device via said connector.
9. An audio accessory apparatus as claimed in claim 7 wherein in the second mode of operation the interface circuitry is configured to provide a second digital signal path from one of the second and third contacts to the digital module, wherein one of said first and second digital signal paths is used to receive digital data from the electronic device and the other of said first and second digital signal paths is used to transmit digital data to the electronic device.
10. An audio accessory apparatus as claimed in claim 1 further comprising at least one additional audio transducer wherein the apparatus is configured such the at least one additional audio transducer is disabled in the first operating mode and enabled in the second operating mode.
11. An audio accessory apparatus as claimed in claim 10 wherein the at least one additional audio transducer comprises at least one microphone.
12. An audio accessory apparatus as claimed in claim 1 wherein said connector is a jack plug.
13. An audio accessory apparatus as claimed in claim 12 wherein said connector is a TRS jack plug or a TRRS jack plug.
14. Audio interface circuitry for an accessory apparatus which can be removably connected to an electronic device via a removable connector, the audio interface circuitry comprising:
a plurality of connector nodes for coupling to respective contacts of the removable connector; and
a first output node for outputting analogue audio signals for driving an audio output transducer;
wherein the audio interface circuitry is operable:
in an analogue mode to forward analogue audio signals received at a first connector node of said plurality of connector nodes to the first output node via an analogue signal path; and
in a digital mode to disable the analogue signal path and forward digital audio signals received at the first connector node to a digital decoder, wherein the digital decoder converts the digital audio signal to an analogue audio signal which is forwarded to the first output node;
wherein in the digital mode the digital decoder is configured to receive an operating power supply from one of said plurality of connector nodes and in the absence of suitable power from the one of said plurality of connector nodes the audio interface circuitry is configured to default to the analogue mode; and
wherein the audio interface circuitry comprises discrimination circuitry configured to, when power is available via the one of said plurality of connector nodes, determine whether to operate in the digital mode and, if so, generate a control signal to disable the analogue signal path.