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DFE-500TX Ethernet PC Card User's Guide
3
Startup communication between the two devices occurs when both devices are
power-on, the cable connection between them is good, and the Network
Operating System software is running. As soon as those conditions are
satisfied, the preparatory process of Autonegotiation between the DFE-500TX
and its supporting hub proceeds automatically. If the hub has Autonegotiation
functionality, then it and the DFE-500TX exchange a series of messages in
which each device signals its capabilities and listens for corresponding
information about the other. The Autonegotiation process requires only a few
milliseconds, and the two devices select the best communication parameters
supported by both devices.
If the hub does not have Autonegotiation functionality, then its monotone
(single capability) message will be recognized by the DFE-500TX’s
Autonegotiation facility, and the DFE-500TX will simply switch to the one of
its own capabilities which matches that of the hub.
When the preparatory procedure of Autonegotiation is completed, then the line
is ready and will provide a data channel which is optimal for the two devices.
The line will remain ready without further Autonegotiation action until the
linkage is broken. Autonegotiation then reoccurs at any time that the linkage is
restored, again making the line ready for optimal data communications.
About PCI Bus
Your DFE-500TX Adapter delivers outstanding performance by fully
exploiting the advanced features of your computer’s PCI bus. DFE-500TX
Adapters utilize the Bus Master Mode of the PCI bus, allowing direct transfers
of Ethernet packet content between computer memory and the adapter’s
controller, thus minimizing network demand on the CPU. The adapter’s
controller function is implemented by a DEC (Digital Equipment Corporation)
Intelligent Ethernet Controller chip, which provides the additional benefit of
reduced command processing overhead.
The working relationship between a DFE-500TX adapter and main memory
working in Bus Master mode is powered by the Bridge/Memory Controller of
the PCI bus. This reduces the CPU role in network operations, thus freeing the
CPU to service other tasks, with resulting improvement in overall computing
(multitasking) performance. At the same time, it produces superior network