Revision 1.10 - July 10, 2008
PPC405EXr – PowerPC 405EXr Embedded Processor
DDR 2/1 SDRAM I/O Specifications
Preliminary Data Sheet
The DDR SDRAM controller times its operation using the internal PLB clock signal and generates MemClkOut from
the PLB clock. The PLB clock is an internal signal that cannot be directly observed. However MemClkOut is the
same frequency as the PLB clock signal and is in phase with the PLB clock signal.
Note: MemClkOut can be advanced with respect to the PLB clock by means of the SDRAM0_CLKTR
programming register. In a typical system, users advance MemClkOut by 90°. This depends on the specific
application and requires a thorough understanding of the memory system in general (refer to the DDR
SDRAM Controller chapter in the PPC405EXr Embedded Processor User’s Manual).
The signals are terminated as indicated in Figure 8 for the DDR timing data and output currents in the following
sections.
Figure 8. DDR SDRAM Simulation Signal Termination Model
MemClkOut0
10pF
120Ω
10pF
MemClkOut0
V
= SOV /2
DD
TT
PPC405EXr
50
Ω
Addr/Ctrl (DDR2)
Addr/Ctrl/Data/DQS/DM (DDR1)
30pF
Note: This diagram illustrates the model of the DDR SDRAM interface used when generating simulation timing data.
It is not a recommended physical circuit design for this interface. An actual interface design depends on many
factors, including the type of memory used and the board layout.
DDR2 SDRAM On-Die Termination Impedance Setting
For all DDR2 applications, the On-Die Termination (ODT) impedance value must be set to 75 ohms in the DIMM
Extended Mode Register (EMR) in order to optimize the data transmission during memory write operations.
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