[SI-LIST] SSTL_18 Class I and SSTL_18 Class II

Hi all,

I am trying to understand the DDR2 terminations.
I understand that DDR2 rely on SSTL_18 logic.
The DDR2 device supports 'Full Drive Strength ' and 'Reduced Drive 
Strength'.
Does SSTL_18 Class I mean 'Reduced Drive Strength' and SSTL_18 Class II 
mean 'Full Drive Strength '?
A typical SSTL_18 Class I environment uses a 25 OHM series resistor(Rs) 
and 50 OHM parallel resistor(Rt) whereas SSTL_Class II environment uses 
a 25 OHM series resistor and 25 OHM parallel resistor.
Is the change in the parallel resistance value due to doubled current in 
class II environment?

many thanks,

Sonu


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