AMD Elan SC520 - At 33.333 Mhz; Figure 9-5 PCI Bus Clocking Example 1: Lightly Loaded System; Figure 9-6 PCI Bus Clocking Example 2: Heavily Loaded System

PCI Bus Host Bridge
9-6 Élan™SC520 Microcontroller User’s Manual
Figure 9-5 PCI Bus Clocking Example 1: Lightly Loaded System
Figure 9-6 PCI Bus Clocking Example 2: Heavily Loaded System
9.3.1.1 Running the Élan™SC520 Microcontroller at 33.333 MHz
The clock that is supplied to the PCI bus (CLKPCIOUT) is exactly the same as the frequency
of the crystal. The ÉlanSC520 microcontroller simply buffers the 33-MHz crystal input and
provides it to the CLKPCIOUT pin. Because crystals have inaccuracies, it is possible that
these inaccuracies cause the period of CLKPCIOUT to become marginally less than 30 ns.
CLKPCIOUT
CLKPCIIN
PCI Device 0
CLK
Notes:
In this lightly loaded system, no clock buffering is required.
Élan™SC520 Microcontroller
CLKPCIOUT
CLKPCIIN
PCI Device 0
CLK
PCI Device 1
CLK
PCI Device 2
CLK
PCI Device 3
CLK
PCI Device 4
CLK
Notes:
In this heavily loaded system, clock buffering is required.
Élan™SC520 Microcontroller