Texas Instruments DM648 DSP - Manual (Page 15)

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REFR
DDR_CLK
DDR_CLK
DDR_CS
DDR_CKE
DDR_RAS
DDR_WE
DDR_DQM[3:0]
DDR_CAS
DDR_BA[2:0]
DDR_A[13:0]
2.4.3 Activation (ACTV)
ACTV
BANK
ROW
DDR_CLK
DDR_CLK
DDR_CS
DDR_CKE
DDR_RAS
DDR_WE
DDR_DQM[3:0]
DDR_CAS
DDR_BA[2:0]
DDR_A[13:0]
Peripheral Architecture
Figure 4. Refresh Command
The DDR2 memory controller automatically issues the activate (ACTV) command before a read or write to
a closed row of memory. The ACTV command opens a row of memory, allowing future accesses (reads or
writes) with minimum latency. The value of DDR_BA[2:0] selects the bank and the value of A[12:0] selects
the row. When the DDR2 memory controller issues an ACTV command, a delay of t
RCD
is incurred before
a read or write command is issued. Figure 5 shows an example of an ACTV command. Reads or writes to
the currently active row and bank of memory can achieve much higher throughput than reads or writes to
random areas because every time a new row is accessed, the ACTV command must be issued and a
delay of t
RCD
incurred.
Figure 5. ACTV Command
SPRUEK5A – October 2007 DSP DDR2 Memory Controller 15
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