Figure 1 shows the original design of the SNO
electronics with ethernet connections between SNObus crates and
standard VME bus crates. Figure 2 shows the
final design with a translator card 
coupling the commercial VME crates with the dedicated SNObus
crates. The major operational difference
is that ethernet - even in the point to point configuration -
can only transfer about 1MB per second between crates, while the
Translator with a fully parallel RS485 path between the XL1 and XL2
objects will easily exceed 8MB per second per crate and will be limited
by the back end configuration of standard VME crates and processors,
not the connection to the SNObus crates. The trigger, low voltage,
and high voltage connections are essentially unchanged between the two figures.
Figure 3 shows a more two dimensional plan of the crate and cable organization without actually detailing the cables involved. Note that the actual number of SNObus crates read into a given VME crate depends upon a number of factors that can't be covered here, but the final configuration must take into account the event building strategy, the lookback trigger scheme, the number of additional commercial VME modules needed for other functions (controls, monitors, computing...), the physical layout of the deck, and, of course, costs.
