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Intel
®
820E Chipset
R
Design Guide 163
4. Clocking
4.1. Clock Generation
Two clock generator components are required in an Intel 820E chipset-based system. The Direct
RDRAM clock generator (DRCG) generates clock for the Direct RDRAM interface, while the CK133
component generates clocks for the rest of the system. Clock synthesizers that meet the Intel CK98 Clock
Specification are suitable for an Intel 820E chipset-based system. The CK133 generates the clocks listed
in the following table.
Table 55. Intel
®
820E Chipset Platform System Clocks
Number Name on CK133 Used for Routed to Name on
Receiver
Frequency Voltage
4 CPUCLK[0–3] System bus clock 2 processors CLK 100/133 MHz 2.5 V
MCH HCLKIN
ITP BCLK
3 APIC[0–2] APIC bus clock 2 processors PICCLK 33 MHz 2.5 V
ICH2 APICCLK
8 PCICLK[1–7,F] PCI bus clock 5 PCI devices CLK 33 MHz 3.3 V
PCI, LPC, FWH Flash
BIOS bus clock
ICH2 PCICLK
FWH Flash BIOS I/F
clock
FWH Flash BIOS CLK
LPC I/F clock LPC CLK
4 3V66[0–3] Hub interface/AGP bus
clock
MCH CLK66 66 MHz 3.3 V
Hub interface clock ICH2 CLK66
AGP bus clock AGP device/ slot CLK
Unused N/A N/A
2 REF[0–1] Internal ICH2 logic ICH2 CLK14 14 MHz 3.3 V
Internal super I/O logic Super I/O Vendor
specific
1 48MHz USB ICH2 CLK48 48 MHz 3.3 V
2 CPU_DIV2[0–1] DRCG reference clock DRCG REFCLK 50/66 MHz 2.5 V
Unused N/A N/A
The CK133 is a mixed-voltage component. Some of the output clocks are 3.3 V, and some of the output
clocks are 2.5 V. As a result, the CK133 device requires both 3.3 V and 2.5 V. These power supplies
should be a clean as possible. Noise in the power delivery system for the clock driver can cause noise on
the clock lines.