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Bus connections and ports
On-Board SCSI Controllers
The system board includes two Adaptec controller chips, channels A and B,
interfacing directly to the second PCI bus.
SCSI bus A
Controlled by an on-board Adaptec AIC7850 having integrated single ended
SCSI drivers for direct connection to an 8 bit fast (10Mhz) bus. Bus
connection is via a 50 pin header. This is a provision for direct control of
devices such as SCSI CD-ROM or Tape drives fitted in the front, removable
media, drive bay.
SCSI bus B
Controlled by an on-board Adaptec AIC7880 similar to the above, but for
connection to either fast (10Mhz) or ultrafast (20Mhz) bus. Bus connection
is via a 68 pin 'P' type connector. This is a very high specification device
aimed at UltraSCSI hard drives.
In both cases the Adaptec SCSI bus is incorporated into the motherboard
BIOS. Both bus systems have active termination, the power supply for which
is protected by a 1A resettable fuse. This in turn is monitored by the system
management cards.
Active negation outputs reduce the chance of data errors by actively driving
both polarities of the SCSI bus and avoiding indeterminate voltage levels and
common-mode noise on long cable runs. The SCSI output drivers can
directly drive a 48 mA, single-ended SCSI bus.
Power Connections
The main power input to the motherboard is via two sets of 5v. connections
at the bottom of the board. These are designed to be fitted with supply
busbars direct to the Power Supply Unit (PSU) located in the bottom of the
server. The PSU functions as an Uninteruptable supply, having a battery
back up in case of mains interruptions or failure, allowing the system to shut
down in a predescribed and orderly manner.
All the other required voltages for add-in EISA/ISA boards, PCI boards, and
the system board are supplied through the auxiliary connector on the lower
right side of the motherboard. All power connector pins are rated at 5
amperes. In addition there are connections at the top of the motherboard for
the supply to the Power Distribution board, which in turn, returns a 3.3 v.
supply required by system logic.
Floppy disk
There is a standard floppy disk interface provided at the top of the
motherboard. This will normal be ribbon cabled to the removable media
drive bay and the 3.5 inch floppy drive. The system can boot from this drive.
M o t h e r b o a r d
12/7
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