DDR SDRAM Clocking and Interface Timing
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
12-17
Figure 12-10. Write Timing Adjustments Example for Write Latency = 1
12.3.4
DDR SDRAM Refresh
The DDR memory controller supports auto refresh and self refresh. Auto refresh is used during
normal operation and is controlled by the DDR_SDRAM_INTERVAL[REFINT] value; self
refresh is used only when the DDR memory controller is set to enter a sleep power management
state or a soft-stop state. The REFINT value, which represents the number of memory bus clock
cycles between refresh cycles, must allow any outstanding transactions to complete before a
refresh request is sent to the memory after the REFINT value is reached. If a memory transaction
is in progress when the refresh interval is reached, the refresh cycle waits for the transaction to
complete. In the worst case, the refresh cycle must wait the number of bus clock cycles required
by the longest programmed access. To ensure that the latency caused by a memory transaction
does not violate the device refresh period, it is recommended that the programmed value of
REFINT be less than that required by the SDRAM. When a refresh cycle is required, the DDR
memory controller does the following:
1.
Completes all current memory requests.
2.
Closes all open pages with a
PRECHARGE
ALL
command to each DDR SDRAM bank
with an open page (as indicated by the row open table).
ACTTORW
ROW
COL
SDRAM Clock
MCS
MCAS
MA[15–0]
MWE
MRAS
00
MDQ[0–31]
MDQS
MDM[0–3]
1/4 Delay
COL
MDQ[0–31]
MDQS
MDM[0–3]
1/2 Delay
0
1
2
3
4
5
6
7
8
9
10
11
12
D0 D1 D2 D3 D0 D1 D2 D3
D0 D1 D2 D3 D0 D1 D2 D3
00
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...