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Intel® Server Platform SR6850HW4 TPS SCSI Backplane Board
Revision 1.0
Intel order number D23151-001
73
7.2 Functional Architecture
This section provides an architectural description of the Server Platform SR6850HW4 SCSI
Backplane Board functional blocks.
7.2.1 SCSI Buses
The SCSI Backplane Board passes the SCSI bus from the Server Board Set SE8500HW4
Mainboard to the internal hot-swap SCSI hard disk drives. Each bus is Ultra320 SCSI low-
voltage differential (LVD) capable. Single-ended (SE) drives are not supported in the hot-swap
disk drive bay. Do not install an internal SE drive because the behavior of the drives is
unpredictable and data corruption could result. This bus is comprised of 68 signals, operating at
an 80MHz clock rate. The SCSI bus is capable of a 320MB data rate, from double transition
(DT) data transfers on a two-byte wide bus. The bus attaches to the Server Board Set
SE8500HW4 Mainboard with a standard 68-pin SCSI connector.
320 MB/s = 2 byte bus * 80 MHz clock * double transitions.
Note: Drives and the SCSI controller on the Server Board Set SE8500HW4 Mainboard
negotiate the actual SCSI bus data rate.
7.2.2 SCSI Drive Power Control
SCSI power control is provided under control of the Programmable Logic Device (PLD). SCSI
power control includes drive power switching, initial power-on charge pumping, over-current
protection, system status notification, and drive status LEDs.
The system is notified when a hot-swap SCSI hard disk drive is detected. The SCSI Backplane
Board applies power to the designated hot-swap SCSI hard disk drive and illuminates the status
LED to provide visual indication of the event.
7.2.2.1 Internal SCSI Drive Power Switching
Each SCSI drive is supplied with +12V and +5V. Separate MOSFET switches are used to apply
and remove +12V and +5V to each hot-swap SCSI hard disk drive.
7.2.2.2 Initial Power-on Charge Pumping
An initial current surge (up to 20A) is applied when power is first applied to a hot-swap SCSI
hard disk drive. To reduce this initial current surge the SCSI Backplane Board charge pumps
the drives for ~700µs. Charge pumping the hard disk drives keeps the average power-on
current to approximately 3A.