I/O Drawer Features; I/O Drawer Addressing - IBM 7026-H80 - RS/6000 - 256 MB RAM Service Manual

I/O Drawer Features

I/O drawers may have two redundant power supplies. One of these power supplies is
capable of providing the necessary voltages and currents independently of the other.
The left and right power supply output voltages are connected and monitored by the
power distribution board contained in the 5 EIA-unit I/O drawer. Both power supplies
provide +12 V dc to the fans in the drawer to ensure sufficient cooling if one of the
supplies fails. However, the short circuit prevention is on the I/O board to protect
against shorts in one output, thus causing the +12 V dc to fail completely.
The left and right power supplies are hot-pluggable and may be changed one-at-a-time
while the system is operational. Each power supply provides 5 V dc, 3.3 V dc, 12 V dc,
and 5 V dc standby power.
The 5 V dc standby power is provided by both power supplies; this can be done
because the power supplies contain overload protection against one supply shorting the
other. Standby power (5 V dc) is provided to the part of the primary I/O drawer planar
on which the SPCN and service processor logic reside.

I/O Drawer Addressing

I/O drawer addressing refers to the drawer number that is displayed in the operator
panel on secondary I/O drawers. This address is the drawer's location in the RIO
(remote I/O) loop. The drawer number is displayed in the form U0.n, where n is the
drawer number. The primary I/O drawer number is 1 by default, but it is not displayed
on the operator panel. The first time that the system is booted after a service action or
configuration change that involves an I/O drawer or its backplane, the system may
detect a duplicate or incorrect I/O drawer number. This situation can result in duplicate
or incorrect drawer numbers being displayed when the system is booting up. The final
drawer number will be assigned and displayed, when the bootup is complete. The
drawer numbers are not reassigned unless a service action or configuration change
occurs.
When ac power has been disconnected from the system or from a drawer, then
reconnected, the I/O drawer address temporarily displays in the format *0n, where n is
the drawer number. After the system is powered on, and the boot sequence has been
initiated, the drawer numbers are restored to the U0.n format.
Chapter 1. Reference Information
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