MSC8144E Reference Manual, Rev. 3
12-10
Freescale
Semiconductor
DDR SDRAM Memory Controller
12.2
JEDEC Standard DDR SDRAM Interface Commands
This section describes the commands and timings for DDR or DDR2 modes. The DDR memory
controller performs all read or write accesses to DDR SDRAM using JEDEC standard DDR
SDRAM interface commands. The SDRAM device samples command and address inputs on
rising edges of the memory clock; data is sampled on both the rising and falling edges of
DQS
.
Data read from the DDR SDRAM is also sampled on both edges of
DQS
.
Following are the DDR SDRAM interface commands (summarized in Table 12-7) provided by
the DDR controller. All actions for these commands are described from the perspective of the
SDRAM device.
Row activate. Latches row address and initiates memory read of that row. Row data is
latched in SDRAM sense amplifiers and must be restored by a precharge command before
another row activate occurs.
Precharge. Restores data from the sense amplifiers to the appropriate row. Also initializes
the sense amplifiers in preparation for reading another row in the memory array,
(performing another activate command). Precharge must occur after read or write, if the
row address changes on the next open page mode access.
Read. Latches column address and transfers data from the selected sense amplifier to the
output buffer as determined by the column address. During each succeeding clock edge,
additional data is driven without additional read commands. The amount of data
transferred is determined by the burst size, which is set to 4.
Write. Latches column address and transfers data from the data pins to the selected sense
amplifier as determined by the column address. During each succeeding clock edge,
additional data is transferred to the sense amplifiers from the data pins without additional
write commands. The amount of data transferred is determined by the data masks and the
burst size, which is set to four by the DDR memory controller.
13
x
10
x
2
MRAS
12 11 10 9
8
7
6
5
4
3
2
1
0
MBA
1
0
MCAS
9
8
7
6
5
4
3
2
1
0
13
x
9
x
2
MRAS
12 11 10 9
8
7
6
5
4
3
2
1
0
MBA
1
0
MCAS
8
7
6
5
4
3
2
1
0
Table 12-6. DDR2 Address Multiplexing for 32-bit Data Bus (Continued)
Row
x
Col
MSB
Address from Core Initiator
LSB
30
29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
8
7
6
5
4
3
2
1–0
Содержание MSC8144E
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