Intel 440GX manual DIMM Solution With FET Switches, Registered SDRAM, F E T, 8 2 4 4 3 G

Models: 440GX

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3.6.2DIMM Solution With FET Switches

Design Checklist

3.6.2DIMM Solution With FET Switches

With existing 64Mbit technology, 512 MB, 1 GB and 2 GB support for servers and workstations must have 4 double sided DIMMs.

500 ohm - 1K ohm pull-down resistors on each of the second inputs (1A2, 2A2, etc.) are recommended on the FET switches (500 ohms is recommended based on simulation) to prevent a direct short to ground while switching.

Figure 3-3. Current Solution With Existing FET Switches

 

 

 

 

D

D

 

DQ 0 - 71

F E T

DQA 0 - 71

I

I

 

 

 

 

 

S W

DQB 0 - 71

M

M

8 2 4 4 3 G X

 

 

M

M

 

 

 

 

 

 

 

0

4

R 0

R 7 1

FENA

 

 

 

 

 

 

 

 

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All 72 DQ lines are fed through the FET switch.

The current FET switch is Pericom PI5C16212A, package type A56. See third-party vendor list for more FET switch vendors.

12 functional units per part requires 6 devices on motherboard.

3.6.3Registered SDRAM

There may be power and thermal considerations for registered DIMMs. If a design is going to support registered DIMMs, the DIMM spacing may need to be evaluated based on mechanical and cooling issues.

REGE, pin 147 on all the DIMMs needs a 0 ohm pull-up to enable registered DIMMs.

Data lines are directly connected to the SDRAM components, while all address and control signals are registered. The clock signal is routed via a PLL to all the SDRAM devices.

Access to registered DIMMs requires an additional clock of leadoff latency, programmable in the 82443GX.

Intel®440GX AGPset Design Guide

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Intel 440GX manual DIMM Solution With FET Switches, Registered SDRAM, 3. Current Solution With Existing FET Switches, F E T