Make it to the Right and Larger Audience
This topic contains 3 replies, has 3 voices, and was last updated by JingZh 5 years, 2 months ago.
So when read data out of DDR mem, DDR outputs DQS and DQ and their toggling edges are aligned. I assume controller still samples data in the middle of data but how? For write access, DDR mem samples data at DQS toggling edge or in the middle?
For read, controller PHY will delay DQS by 90° so that DQS toggles right in the middle of DQ.
For write, yes, DDR samples DQ at DQS toggling edges.
My understand is no matter read or write, DQ(Data) is always aligned with clock edges. For read, DQS 90º adjust is done by controller. For write, DQS adjust is done by DDR memory. Is above right?
Correct for read access. For write, actually DQS is aligned with clock and DQ has a 90 degree phase shift since DQS toggles in the middle of DQ.
Here is a good tutorial about how DDR mem works. Check section 9.
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