Intel 820E 2.7.5. Direct RDRAM* Clock Routing , 2.7.6. Direct RDRAM* Design Checklist

Intel® 820E Chipset
R
Design Guide 57
2.7.5. Direct RDRAM* Clock Routing
Refer to Chapter 4 Clocking for the Intel 820E chipset platform’s Direct RDRAM clock routing
guidelines.
2.7.6. Direct RDRAM* Design Checklist
Use the following checklist as a final check to ensure that the motherboard incorporates solid design
practices. This list is only a reference. For correct operation, all of the design guidelines within this
document must be followed.
Table 9. Signal List
RSL Signals High-Speed
CMOS Signals Serial CMOS Signal Clocks
• DQA[8:0]
• DQB[8:0]
• RQ[7:0]
• CMD
• SCK
• SIO • CTM
• CTM#
• CFM
• CFM#
• Ground isolation well grounded.
 Via to ground e very 0.5 inch around edge of isolation island
 Via to ground every 0.5 inch between RIMMs
 Via to ground every 0.5 inch between signals (from MCH to first RIMM)
 Via between every signal within 100 mils of the MCH edge and the connector edge
 No unconnected ground floods
 All ground isolation at least 10 mils wide.
 Ground isolation fills between serpentines
 Ground isolation not broken by C-TABs.
 Ground isolation connects to the ground pins in the middle of the RIMM connectors.
 Ground isolation vias connect on all 4 layers and should not have thermal reliefs.
 Ground pins in RIMM connector connect on all 4 layers.
• VTERM layout yields low noise.
 Solid VTERM island is on top layer. Do not split this plane.
 Ground island ( for ground side of VTERM caps) is on top.
 Termination resistors co nnect directly to the VTERM island on the top layer (without vias).
 Decoupling VTERM is critical!
 Decoupling capacitors connect directly to top-layer VTERM island and top-layer ground island.
(See the layout example.)
 Use at least 2 vias per decoupling capacitor in the top-layer ground island.
 Use 2 × 100 µF tantalum capacitors to decouple VTERM. (Aluminum/electrolytic capacitors are
too slow!)
 High-frequency dec oupling capacitors must be spread out across the termination island so that
all termination resistors are near high-frequency capacitors.
 100 µF tantalum capacitors should be at each end of the VTERM island.
 100 µF tantalum capacitors must be connected directly to VTERM island.
 100 µF tantalum capacitors must have at least 2 vias/cap to ground.
 VTERM island should be 50–75 mils wide.
 VTERM island should not be broken.