> Nice question itself. Here is a thought. Could the clock line(s) pick up
> interference since they would be *longer* than the standard practice?
>
> John
>


I think the larger concern is transmission line reflections. If the traces
go to exactly one location, you can use series termination at the source..
If its a bus driving several devices along the way, you need parallel
terination at the far end. If it's a multi-drop bus where several devices
along the line can drive it (not all at once, and pretty unlikely for a
clock), you need a parallel termination at each end. A clock distribution
chip is nice in that you have separate output for each line. You can drive
several lines with one output if it's a zero ohm output (lotsa current
capability). Otherwise, part of the source termination is in the chip and
things get messy driving multiple lines.

It's interesting to watch a line at the driver, right after the series
source termination. The line will go to 50% voltage, then, when the
reflection comes vack from the far end, go to 100% voltage. At the far
end, the voltage just goes straight to 100%.

Harold



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