Outline Of The 1394 Unit - Pioneer VSX-56TXi Service Manual

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7.1.4 OUTLINE OF THE 1394 UNIT

Operational Outline of the IEEE 1394 Unit
This unit supports the A&M protocol (Audio and Music Data transmission Protocol), which, among the IEEE 1394 audio and video
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protocols, is employed for audio equipment and electronic musical instruments, etc. As the unit does not support the MPEG2-TS protocol
(for BS digital tuners and D-VHS) or the DV protocol (for digital video cameras and Pioneer's DVR) among IEEE 1394 audio and video
protocols, it does not support video data transmission.
The main commands supported by this unit are: For sending, the PLAY command to a player, and for receiving, the commands for
switching functions, increasing/decreasing the volume, muting on/off, and stream information (for inquiring about the receiving
capabilities of the receiver).
Audio data (media) that can be received by the unit are as follows:
• DVD-A (2 channels, multiple channels)
• SACD (2 channels, multiple channels)
• IEC 60958 (DVD-V, DVD-RW, CD, VCD, MP3, DTS-CD, etc.)
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The received data are demodulated separately for the above three signal formats in the IEEE 1394 receiving IC, output to another IC for
jitterless transmission, then output to a third IC for DIR or to the DSP of the main unit.
As to SACD data, DSD streams are converted to multibit data at the SACD/PCM converting IC, and this enables SACD data processing at
the DSP of the main unit. But DSD streams are inputted directly into the DAC bypassing the DSP at SACD DIRECT mode.
In jitterless transmission, audio data with jitter generated during IEEE 1394 transmission (actually, jitter contained in sync signals that
cannot be reduced by the PLL for audio receiving) are cached in the buffer RAM in the receiver up to a certain amount, and then read out
by a highly accurate crystal-oscillation clock in the receiver, which enables reduction of jitter. The receiver controls the amount of cached
data in the buffer RAM such that a certain amount of data is always cached. If the amount of cached data falls below the specified level, a
request is sent to increase the playback speed (transmission volume per unit hour) (+1%). If the amount of cached data exceeds the
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specified level, a request is sent to decrease the playback speed (-1%). Thus, data transmitted in jitterless transmission are delayed by about
0.7 sec behind the time indicated on the FL of the transmitting device, compared with data transmitted in normal transmission. Moreover,
as mentioned above, because the sending device switches the system clock according to the request of the receiving device, sync of the
video signal may be unlocked, and the audio signal would be delayed behind a video signal because of its being cached. So many sending
devices do not adopt jitterless transmission for content having both audio and video signals.
Both the sending and receiving devices must support jitterless transmission to enable this type of transmission. Start of jitterless
transmission is requested by the receiving device; however, depending on the status of the sending device (type of media, etc.), jitterless
transmission may not be possible. Media for which jitterless transmission is supported and those for which it is not (only normal
transmission is supported) are shown below:
• Jitterless transmission
• Normal transmission only : DVD-V, DVD-RW, VCD, MP3
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Depending on the specifications of the sending device, it may not support jitterless transmission, even for those media for which it can be
supported.
As to copyright protection, IEEE 1394 employs the DTCP (Digital Transmission Content Protection) system, which consists of the
following:
1. Copy-control information
2. Authentication and key exchange
3. Encryption
4. System renewability
The procedures for copy protection are basically as follows: After authentication and key exchange for encryption/decryption, the sending
device will send the data encrypted using the keys. The receiving device in turn will decipher the data using the exchanged keys.
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• Media whose data can be encrypted: DVD-V, DVD-A, SACD, DVD-RW
• Media whose data cannot be encrypted: CD, DTS-CD, VCD, MP3
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: DVD-A, SACD, CD, DTS-CD
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