Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-03-13
2001-12-04
Holloway, III, Edwin C. (Department: 2635)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S503000, C370S465000, C369S059270
Reexamination Certificate
active
06327272
ABSTRACT:
The invention relates to a data transfer system comprising a transmitter and at least one receiver; the transmitter and receiver being connected by a data line for time-multiplexed transfer of data words. The invention further relates to a transmitter for time-multiplexed transfer of data words via a data line. The invention also relates to a receiver for receiving time-multiplexed data words via a data line.
U.S. Pat. No. 4,755,817 describes a data transfer system, known as I
2
S (Inter-IC Sound), which is widely used for transferring digital audio data between digital audio components, such as digital input/output interface, including A/D and D/A converters and IEC 958 transceivers, digital filters, digital error correctors, dedicated digital coders/decoders and general purpose digital signal processors. The transmitter and receiver(s) are connected via three signal lines: a clock signal (SCK), a word-select signal (WS) and a serial data signal (SD) line. The data is serially transferred from the transmitter to the receiver(s) via the serial data line, in synchronisation with periodic clock pulses of the clock signal. The transmitter and the receiver(s) are synchronised to the same clock signal. I
2
S supports data transfer for two channels (the first and second channel, corresponding to the left and right audio channel respectively). The data of the channels is transferred in a time-multiplexed manner: transfer of a data word of the left channel is followed by transfer of a data word of the right channel and vice versa. The length of a data word is variable, up to 32 data bits. The two-level word-select signal controls the transfer of the data words. A change of the signal level indicates the start of the transfer of a new data word. The transmitter comprises for each data channel a corresponding channel register. A register selection means of the transmitter selects from which of the two channel registers a data word is transmitted. When the word-select signal becomes low (‘0’) the first channel register, corresponding to the left channel, is selected and when the word-select signal become high (‘1’) the second channel register, corresponding to the right channel, is selected. As such, the duration of the word-select signal in clock pulses indicates the length of the data word and the level of the signal indicates to which channel the data word corresponds. In a manner analogue to the transmitter, the receiver comprises two channel registers and a register selection means which operate for receiving data words.
For digital audio channels, the audio data is typically encoded using a linear-PCM coding, where a PCM word corresponds one-to-one to an I
2
S word. It is, however, allowed that the transmitter and receiver operate with a different word-size than used at system level and indicated by the word-select signal. Also the transmitter and receiver word lengths may be different. To guarantee compatible operation when different word-sizes are used, a data word is transmitted starting with the most significant bit (MSB). If the transmitter word is longer than the system word, only the most significant part of the transmitter word is transmitted with a number of bits corresponding to the length of the system word. If the transmitter word is shorter than the system word, the transmitter word is complemented for transmission with the required number of ‘0’ bits at the least significant bit positions to form a word having the same length as the system word. Similarly, if the receiver word is shorter than the received word only the most significant bits of the received word that fit into the receiver word are processed. If the receiver word is longer, the received word is complemented during reception with the required number of ‘0’ bits at the least significant bit positions to form a word having the same length as the receiver word. Instead of linear-PCM, other coding formats, such as MPEG-1 or MPEG-2, may be used as well in combination with a suitable manner of packaging the coded data in data words for transfer via I
2
S. WO patent application PCT/IB96/01267 (PHN 15603) describes a burst format of the MPEG encoded audio for transfer via the IEC 958 transmission system, which uses a same frame sampling rate and contains the same number of data bits in a frame as I
2
S . The data format described in the burst format may, advantageously, also be used for transfer of data via I
2
S.
In a typical application, I
2
S is used in a CD player for transfer of the two-channel digital audio read from a CD to an audio decoder for producing an analogue output signal for the left and right audio channel. The digital audio is also transferred via 1
2
S to an IEC 958 interface (also referred to as SPDIF) for transfer in a digital form to another device, such as a digital amplifier or recording device.
Increasingly, audio systems, such as surround sound systems, process more than a left and right audio channel. In fact, present-day MPEG2 technology has standardised five audio channels (plus one support channel): a Left, Right, Centre, Left Surround, Right Surround, and furthermore a low frequency enhancement (LFE) channel. Typically, the channels are read from a digital medium, such as a Digital Video Disc (DVD), in an encoded form and decoded, for instance by an MPEG decoder. DVD also supports a variable number of up to eight linear-PCM audio channels. The decoded MPEG audio channels or the linear PCM audio channels may be transferred to a local audio decoder for producing an analogue output signal for, for instance, the left and right audio channel. The audio channels may also be transferred in a digital form to a separate audio reproduction device, such as a surround amplifier, or a recording device. The transfer from the player device to the audio reproduction device or recording device may take place via the IEC 958 protocolled interface. For certain basic systems or certain applications (e.g. playing a CD), local transfer of two channels may be sufficient. For more advanced systems or applications (e.g. playing a DVD), local transfer of more than two channels is required.
I
2
S is designed for isochronous transfer of two-channel digital data and has no provisions for transferring data for more channels.
It is an object of the invention to provide a system, transmitter and receiver capable of transferring isochronous data for more than two channels. It is a further object that such a system, transmitter and receiver are based on I
2
S, simplifying (re-)design of components and enabling to cost-effectively provide components which are compatible with I
2
S.
To achieve this object, the data transfer system according to the invention comprises a transmitter and at least one receiver; the transmitter and receiver being connected by a data line for time-multiplexed transfer of data words of, in a first mode, up to a predetermined number N of data channels; N being larger than two and each data word comprising at least one data element. The transmitter comprises a sequence of N channel registers, each corresponding to a different one of the data channels; register selection means for selecting one of the channel registers for supply of a data word for transmission; the selection comprising selecting a first one of the channel registers in synchronisation with a frame-begin signal, and selecting a next one of the channel registers in synchronisation with a regular trigger provided by a word-select signal; the frame-begin signal having priority over the word-select signal; and means for, in synchronisation with a periodic clock signal, transmitting a data word from the selected channel register via the data line. The receiver comprises a sequence of N channel registers, each corresponding to a different one of the data channels; register selection means for selecting one of the channel registers for receipt of a data word; the selection comprising selecting a first one of the channel registers in synchronisation with the frame-begin signal, and selecting a next one of the channel registers in sync
Biren Steven R.
Holloway III Edwin C.
U.S. Philips Corporation
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