User`s guide

Appendix A • 53
A.2.1 Hot Swap Controller Hardware Interface
The US1010 low dropout regulator generates the 1V pre-charge voltage for
the data bus lines. The output of the US1010 is set to 1.8V, but the voltage
is further dropped by the 1N4148 diode to generate the 1V. The pre-charge
circuit is capable of sourcing and sinking 40mA.
The hot-swap controller also supports bi-directional pin, l_stat. This signal
is a micro-switch sensor input and a LED control output. The ejector
handles a n on-board micro-switch that controls the l_stat signal, which in
turn controls the LED and indicates to the 21555 when the ejector is open
or closed.
The LED may also be controlled independently of the micro-switch and
hot-swap functionality by writing the LED On/Off (LOO) control bit in the
hot-swap control register.
The figure below shows how the l_stat signal is implemented. The 21555
assumes that the local reset signal, which is asserted upon card removal
or insertion, is OR’ed with the primary bus reset on the card, and then input
to the 21555’s p_rst_l reset input.
Figure 5: l_stat Signal Implementation