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DDR_CLK
DDR_CKE
DDR_CS
DDR_WE
DDR_CAS
DDR_DQM[1:0]
DDR_D[15:0]
DDR_A[13:0]
DDR_RAS
DDR_DQS[1:0]
COL
BANK
DDR_A[10]
DDR_BA[2:0]
CAS Latency
D0
D1
D2
D3
D4
D5
D6
D7
DDR_CLK
Architecture
378
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
DDR2/mDDR Memory Controller
14.2.3.4 READ Command
shows the DDR2/mDDR memory controller performing a read burst from DDR2/mDDR
SDRAM. The READ command initiates a burst read operation to an active row. During the READ
command, DDR_CAS drives low, DDR_WE and DDR_RAS remain high, the column address is driven on
DDR_A[13:0], and the bank address is driven on DDR_BA[2:0].
The DDR2/mDDR memory controller uses a burst length of 8, and has a programmable CAS latency of 2,
3, 4, or 5. The CAS latency is three cycles in
. Read latency is equal to CAS latency plus
additive latency. The DDR2/mDDR memory controller always configures the memory to have an additive
latency of 0, so read latency equals CAS latency. Since the default burst size is 8, the DDR2/mDDR
memory controller returns 8 pieces of data for every read command. If additional accesses are not
pending to the DDR2/mDDR memory controller, the read burst completes and the unneeded data is
disregarded. If additional accesses are pending, depending on the scheduling result, the DDR2/mDDR
memory controller can terminate the read burst and start a new read burst. Furthermore, the DDR2/mDDR
memory controller does not issue a DAB/DEAC command until page information becomes invalid.
Figure 14-8. DDR2/mDDR READ Command