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Chapter 8. FireWire > 1394-1995 Cable Physical Layer Attributes

8.2. 1394-1995 Cable Physical Layer Attributes

The 1394 shielded twisted pair cable-based physical layer can be characterized by its packet format, transceiver circuit, DATA/STROBE line code, and PSDs.

8.2.1. Packet Formats

There are three types of packets exchanged between FireWire transceivers. There are physical layer packets used during initialization and link management, primary packets for carrying asynchronous and isochronous data, and an acknowledge packet for reception of asynchronous packet acknowledgment. The general format of the physical layer packet is shown in Figure 8.15. The first 4 bytes of a physical layer packet consists of a packet type of 2 bits, a physical_ID of 6 bits, and a body of 3 bytes. The last 4 bytes of a physical layer packet are the logic inverse of the first 4 bytes for error detection parity checking. A physical layer packet is ignored if the logic inverse of the last 4 bytes does not match the bit pattern of the first 4 bytes.


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