I/O Subsystem
R
Intel
®
855PM Chipset Platform Design Guide
203
Table 54. Bus Capacitance Reference Chart
Device
# of Devices/
Trace Length
Capacitance Includes
Cap (pF)
ICH4-M 1
Pin
Capacitance
12
CK408 1
Pin
Capacitance
10
2
28
SO-
DIMMS
3
Pin Capacitance (10 pF) + 1 inch worth of trace capacitance (2 pF/inch)
per SO-DIMM and 2 pF connector capacitance per SO-DIMM
42
2
86
3
129
4
172
5
215
PCI
Slots
6
Each PCI add-in card is allowed up to 40 pF + 3 pF per each connector
258
≥
24
48
≥
36
72
Bus
Trace
Length
in inches
≥
48
2 pF per inch of trace length
96
Table 55. Bus Capacitance/Pull-Up Resistor Relationship
Physical Bus Segment Capacitance
Pull-Up Range (For Vcc = 3.3 V
0 to 100 pF
8.2 k
to 1.2 k
100 to 200 pF
4.7 k
to 1.2 k
200 to 300 pF
3.3 k
to 1.2 k
300 to 400 pF
2.2 k
to 1.2 k
