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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