A method and apparatus for performing logical attachments and detachments
in a hot-plug-in data bus is described. A hot-plug-in data bus may utilize
pull-down resistors to keep bus signals near a low voltage level when bus
units are physically detached. Active pull-up resistors may then raise the
bus signals away from ground when the bus units are physically attached
via cabling or other forms of interconnection. The pull-up resistors may
be switched away from the pull-up voltage source, which allows the
remaining pull-down resistors to pull the bus signals down to the voltage
levels corresponding to physical detachment of the cabling.
