Hot-Swap Capability
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Model 6476 User Guide
3 • System Architecture
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Hot-Swap Capability
Hot-swapping is the capability of removing and replacing components without turning off the system. Hot-
swap capability is becoming increasingly important in systems requiring continuous operation at some level.
Because boot times of many popular operating systems are long, the hot-swap capability is crucial for high-end
PC servers, and even more so for telecommunication systems, such as base stations, where board-level
exchanges must be made without any downtime. CompactPCI supports dynamic configuration to allow hot
removal/insertion of boards without interrupting backplane transactions or disturbing DC voltages in the
power system.
The hot-swap feature is implemented on the CPCI boards, not on the backplane. The backplane remains pas-
sive. Therefore, CompactPCI boards either are or are not hot-swappable.
Signal lines must be precharged to 1V before being plugged into the backplane to maintain ongoing bus trans-
actions. Also, power must be ramped up or down in a controlled manner to allow the power supply to adjust to
the change in load. The power supply, ground and signal pins on the connectors are staged to allow sequenc-
ing, so as to not disturb the operation of the surrounding boards in the bus. The three levels of sequencing are:
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Short pins for BD_SEL#
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Medium pins for signals
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Long pins for power/ground
The system uses two levels of sequencing so that power/ground is made first/broken last. The short pin
(BD_SEL#) connection is made only when the board is firmly seated, which signals the control circuitry to
power up any high-current devices. Conversely, BD_SEL# breaks first to provide early warning to the
control circuitry.
The dual frame ground lugs on DC interfaces must be used to connect the chas-
sis to earth ground. Failure to do this will cause excessive RF emissions and
could possibly create a safety hazard.
WARNING
