I/O Drawer Features; I/O Drawer Addressing - IBM RS/6000 Enterprise Server M80 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 of U0.n, where n is the drawer number. The drawer number is not displayed on the
primary I/O drawer operator panel but it is assumed to be *01 (or U0.1). The first time you boot the system
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 chance occurs.
When ac power (dc power in a dc-powered system) has been disconnected from an I/O drawer and then
reconnected, the I/O drawer addresses on the secondary drawers will temporarily appear 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 will be restored to the U0.n format.
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Service Guide