Alan,
I attended a DDR presentation and some slides said:
PC Applications: PC266 Devices, PC2100 Modules, 1-4 slots, Long traces < 12", Termination, No Dummy modules
Small Systems: SS-400 Devices, Direct Connect, 2-8 DDR SDRAMS, Short traces < 2", No termination, Built for speed
DDR Signaling: SSTL_2 differential inputs, 2.5V I/O with 1.25V reference voltage, Low voltage swing with termination, Rail to rail if unterminated
So I guess that for 8 or fewer DDRs you can go unterminated but if a larger system you got to terminate. I think that the terminatiion method is to provide a series resistor at the source and a pullup at the destination. |
