Relative Bus Delay-Time Space Mode

Ideal first-incident-wave switching required
Very low-capacitance custom transceivers
Detailed attention to timing & reflections budget

Example: Ethernet 10BASE-5

• 2000 meters long (10,000 ns)
• 10 MHz clock (100 ns)
• bus timing ratio 100.

Probably among the premier examples of this type of system is the original Ethernet 10-Mbs coax-based system. This system bears the moniker 10BASE-5.

The original Ethernet operates at a relatively pedestrian rate of 10 MHz, which doesn't sound like much until you realize that with repeaters it can span up to 2-km.

At that maximum radius there can be more than 100 bits in storage, distributed along the cable, at any given time.

The 10BASE-5 Ethernet system is a serial data communications system which encodes its clock as part of the data stream. The clock is extracted by PLL circuits within each receiver. There is an elaborate distributed-control algorithm for deciding who gets to talk when.

Ethernet serves as an extreme example of a large bus timing ratio. If we study this example, it may provide some clues as to how we achieve the printed-circuit board bus structures of the future.

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