Matrox Meteor-II /1394 Installation And Hardware Reference page 24

24 Chapter 4: Hardware reference
Link Layer
Galvanic isolation
barrier (optional)
The link layer (Link) is the second component in the
bi-directional interface between the physical layer (PHY) and
PCI bus. The Link is a PCI-to-1394 Host controller and is
compliant with both PCI and 1394 OHCI specifications. The
link layer supports both asynchronous and isochronous data
transfer between nodes. When transmitting packets, the Link
must send a request to the PHY, which controls the direction of
transmission between the two layers. The link layer also
controls the transfer speed between itself and the PHY, and
supports data transfers of 100, 200, or 400 Mbits per second. In
addition, the Link is capable of transferring a cacheline of data
at 132 Mbytes per second over the PCI bus after connecting to
the memory controller on the Host. In order to overcome high
or long PCI latency, the link layer also provides deep FIFOs.
The optional galvanic isolation barrier isolates the Matrox
Meteor-II /1394's ground from that of the 1394 network. For
example, 1394 network could consist of several PCs, or other
devices such as a digital television or digital VCR. If each device
in the network has a different ground, a potential difference is
created across them; this situation is called a ground loop, and
can eventually lead to loss of data, or even damage to system
components. If a power surge occurs, the circuit tries to ground
excess power, but the Matrox Meteor-II /1394 would be
protected because its ground is isolated from the rest of the
network.