Networking Silicon — 82551IT
11.4
Timing Specifications
11.4.1
Clocks Specifications
PCI Clock Specifications
11.4.1.1
The 82551IT uses the PCI Clock signal directly. Figure 20 shows the clock waveform and required
measurement points for the PCI Clock signal. Table 55 summarizes the PCI Clock specifications.
Figure 20. PCI Clock Waveform
0.6VCC
0.475VCC
0.4VCC
0.4VCC p-to-p
(minimum)
0.325VCC
0.2VCC
T_low
T_high
T_cyc
Table 55. PCI Clock Specifications
Symbol
Tcyc
Parameter
Min
Max
Units
Notes
T1
T2
T3
T4
CLK Cycle Time
CLK High Time
CLK Low Time
CLK Slew Rate
30
11
11
1
ns
ns
1
Thigh
Tlow
ns
Tslew
4
V/ns
2
NOTES:
1. The 82551IT will work with any PCI clock frequency up to 33 MHz.
2. Rise and fall times are specified in terms of the edge rate measured in V/ns. This slew rate is met across the
minimum peak-to-peak portion of the clock waveform as shown in Figure 20.
11.4.1.2
X1 Specifications
X1 serves as a signal input from an external crystal or oscillator. Table 56 defines the 82551IT
requirements from this signal.
Table 56. X1 Clock Specifications
Symbol
Parameter
Min
Typical
Max
Units
Notes
T8
T9
Tx1_dc
Tx1_pr
X1 Duty Cycle
X1 Period
40%
60%
40
ns
±30 ppm
Datasheet
81
INTEL [ INTEL ]
