1.2 Disk Chassis
1.2.2 MUX Printed Circuit Board
Using the MUX PCBs, the DA controller can access up to two banks of disks in
any one PDA enclosure. The MUX PCBs also provide disk status to the PDA
lightpipe and to the disk canister indicators.
The MUX circuitry can be divided into five functional blocks:
• Read data, read clock, drive selected, and command complete multiplexing
• Write data and clocks from array controller to disks
• Provide status to lightpipe indicators
• Provide status to disk canister indicator
• Provide disk sector-pulse monitoring
1.2.2.1 Data Multiplexing
The MUX circuitry multiplexes four groups of signals, two to one:
• Read data (rd)
• Read clocks (rc)
• Command complete (cc_)
• Drive selected (ds_)
The MUX receives read data and read clocks from two different banks, determines
which bank is selected, and passes the appropriate read data and clocks to the
controller.
1.2.2.2 Write Data
Write data and clock signals from the array controller are routed to the bank
selected by the array.
1.2.2.3 Sector Pulse Monitor
The sector monitor is a retriggerable monostable multivibrator. Sector pulses
from the disk keep the output active. If the sector pulse is lost, the output goes
low, signaling that the disk is spun down.
1.3 DPU-PDA Interface Cable
Two 50-pin DPU-PDA interface cables interface the DA controller to the VME 6U
interface PCB (mounted on a Parallel VME 6U Adapter PCB) in the DPU. One
cable carries control information (command/status); the other cable carries data
signals.
1.4 Power/Fan Tray
The power/fan tray mounted in the bottom of the enclosure contains the complete
power subsystem and the exhaust fan, including AC power connection, 20 A and
1 A circuit breakers. Figure 1–11 provides front and side views of the power/fan
tray.
A set of power distribution connectors allows the complete tray to slide in and
out of the enclosure without having to bolt or unbolt power cables. Only the AC
power cable, the temperature sensor cable, and the lightpipe power cable need to
be detached before removing the tray.
Parallel Disk Array Overview 1–13
