B-1
B
Appendix B
Calculating RCIM Cable Propagation Delays
This appendix provides calculations to determine if your cable connections introduce
signal delays.
RCIM III
2
The maximum cable length between each interconnected RCIM III board is 30 meters
(~100 feet).
The clock runs at 400ns per tick. If the clock signal takes more than 400ns to make it to
any given slave in the chain, clock skew will occur from that point on. The clock is re-
driven by each pass-through slave.
Due to synchronization and re-drive of the serial data on the cable, each RCIM III added
to an RCIM chain adds about 50ns of delay in addition to approximately ~7ns for each
meter of the cable, or ~200ns per 30 meter cable.
Two systems in an RCIM chain with the 30 meter cable will operate within a 400ns clock
tick. Having more than two results in less precise synchronization.
Note that if a pass-through slave system is powered off, the cable clock will not be
propagated to the slaves downstream from it. In this case, the downstream slaves will use
their local oscillator instead of the cable clock.
The user just needs to be aware of the delays associated with each RCIM and cable in a
chain to determine if the level of clock skew is acceptable for the application.
RCIM II
2
The maximum cable length between each interconnected RCIM II board is 30 feet.
The clock runs at 400ns per tick. If the clock signal takes more than 400ns to make it to
any given slave in the chain, clock skew will occur from that point on. The clock is
redriven by each pass-through slave.
Due to synchronization and redrive of the serial data on the cable, each RCIM II added to
an RCIM chain adds about 150ns of delay in addition to approximately 2ns for each foot
of the cable, or 60ns per 30 foot cable.
Three systems in an RCIM chain will operate within the desired 400ns. Having more than
three results in less precise synchronization.
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