Samsung M395T5160QZ4 M395T5160QZ4-CF760 Manuale Utente

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There are many frequency parameters including reference clock frequency, DRAM clock frequency, DRAM data transfer rate, channel
transfer rate and channel unit interval. All of frequency parameters are scaled with a certain gear ratio. External clock source provides
reference clock input to AMB and Host. External clock source is relatively slower than channel and DRAM frequency. Thus, AMB dou-
bles external clock input and generates clock inputs to DRAMs. DRAM use clock input from AMB which is two times faster than refer-
ence clock for DRAM operation. DRAM data transfer rate is two times faster than DRAM clock input with nature of double data rate
operation and four times faster than external clock source. Channel speed is represented by unit interval - average time interval between
voltage transitions of a signal in the FBD channel. It is six times faster than DRAM data transfer rate. For example, external clock source
gives 6ns clock (166MHz), AMB doubles it and gives 3ns clock (333MHz) to DRAM and FBD channel communicate with unit interval -
250ps (4.0Gbps transfer rate).

Figure 2 shows frequency scale ratio over frequency parameters in FBD memory system.

DDR2-533

312.5ps

266MHz

133MHz

3.2Gb/s

DDR2-667

250ps

333MHz

166MHz

4.0Gb/s

DDR2-800

208.33ps

400MHz

200MHz

4.8Gb/s

Host

DRAM

DRAM

AMB

DQs ADDR

CMD

CLK

Tx

Tx

Rx

Rx

Clk_Ref

SB (ADDR, CMD, Wdata)

NB(Rdata)

DRAM

DRAM

Clock

Reference CLK

Reference CLK

DDR667 Ex.

6ns

3ns

250ps

CLK_REF

CLK_DRAM

Packet T/F

12 UIs in one CLK_DRAM