Essentially, the IEEE - 1394 FireWire bus uses a memory mapped communication protocol. 1394 transactions can be considered to be a read or write of data to a specified memory address. 1394 uses 64bits of addressing: 16 bits for bus and node addressing with each node (or device) on the bus having 48 bits of address space. The IIDC specification defines how the address space on an IIDC compliant camera is implemented.
The 1394 spec uses big endian notation, that means that means that the most significant byte comes first and the most significant bit is bit 0. The PC uses little endian notation, where the least significant byte comes first.