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Politics : Formerly About Advanced Micro Devices

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To: Joe NYC who wrote (108700)	5/1/2000 1:19:00 AM
From: Tenchusatsu	Read Replies (2) of 1571826

Jozef and others, re: quad-pumping, For double-pumped buses, it's a common misconception to think that the data is being latched on the rising and falling edges of the main clock signal. In fact, when data is sent down a double-pumped bus, strobes (both positive and negative) are sent along with the data. Then the data is latched off the rising and falling edges of the strobes. These strobes are essentially square waves, just like a clock signal, and in fact they run at the same frequency as the clock. However, the phase of the strobes are such that the edges line up with the data. Then with the phases all lining up, the strobes and the data are sent in parallel. Because of this parallel transmission, the phases (hopefully) stay lined up from sender to receiver. A quad-pumped bus would have strobes running at twice the frequency of the main clock. Combine 2x the frequency with rising and falling edges, and you have 4x the data rate. This is how it's done on the Itanium bus (2x133) and on the Willamette/Foster bus (4x100). I don't know how it's done on DDR, but I'd imagine it's pretty similar. Tenchusatsu

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