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Functional Description 4–15
DC Power Distribution
4.7 DC Power Distribution
The AlphaPC 164SX derives its system power from a user-supplied PC power sup-
ply. The power supply must provide +12 V dc and −12 V dc, −5 V dc, +3 V dc, and
+5 V dc (Vdd). The dc power is supplied through power connector J2 , as shown in
Figure 4–8. Power is distributed to the board logic through dedicated power planes
within the six-layer board structure.
Figure 4–8 shows that the +12 V dc, −12 V dc, and −5 V dc are supplied to ISA con-
nectors J22 and J23. The +12 V dc and −12 V dc are supplied to ISA connectors and
PCI32 connectors J15 and J17. The +12 V dc is also supplied to the CPU fan connec-
tor J14, and auxiliary fan connector J16. Vdd (+5.0 V) is supplied to ISA connectors,
PCI32 connectors, and most of the board’s integrated circuits. Vdd also drives the
+2.5-V regulator, which supplies the 21164PC microprocessor.
Figure 4–8 AlphaPC 164SX Power Distribution
+12 V
−12 V
+5 V (Vdd)
−5 V
Gnd
+3.3 V
10
12
4, 6,
19, 20
18
1, 2, 11
3,5,7,13,
15,16,17
ISA Conn.
PCI32
Conn.
Spkr
Conn.
Integrated
Circuits/Clocks
Fan
CPU
Fan
21164PC
+2.5-V
Regulator
+3.3-V Pull-Ups
Pull-Downs
+5-V
Pull-Ups
Power Connector J2
PCI64
Conn.