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Backplane power distribution
32
Model 6276 User Guide
3 • System architecture
ommends that this configuration be maintained. However, in certain specific circumstances, users may wish
to connect these two potentials by installing a jumper between J4 and J5.
•
Shelf Geographic Address (SGA)
—S1 has a DIP switch that enables the user to configure the shelf enu-
meration feature, used for multi-shelf CompactPCI systems. The SGA effectively becomes a chassis identi-
fication code, which is used to uniquely identify the chassis in a multi-chassis environment. This is
currently not used in most ForeFront applications, as most cards/devices are uniquely identified by an IP
address, which is manually configured for each device in the system.
Slot designation
Consistent with CompactPCI specifications, the cPCI bus segment consists of one system slot, and three
peripheral slots. The system slot is located in the first slot, or bottom slot in the 2U model.
The system slot provides arbitration, clock distribution, and reset functions for all boards on the segment. The
system slot performs system initalization by managing each local board’s IDSEL signal. The peripheral slots
may contain simple boards, intelligent slaves, or PCI bus masters.
CompactPCI defines slot numbering based on the concept of physical and logical slots. Physical backplane
slots are designated 1, 2, 3, through N, where N is the number of slots. Physical slot numbering starts at the
bottom slot on the 2U Model 6276 Backplane/Midplane.
Logical slot numbers are defined by the IDSEL signal and associated address used to select the slot. Logical
numbers are used in the nomenclature to define the physical outline of a connector on a bus segment. Logical
and physical slot numbers may not always coincide.
Backplane power distribution
Power is distributed in a CompactPCI system via the backplane. The backplane provides standard direct cur-
rent (DC) supply voltages as specified in
table 5
below:
Table 5. Power specifications
Mnemonic Description Nominal Value Tolerance
5 V
+5 VDC
5.0 V
±5%
3.3 V
+3.3 VDC
3.3 V
±5%
+12 V
+12 VDC
12.0 V
±5%
-12 V
-12 VDC
-12.0 V
±5%
GND
Ground