MCF548x Reference Manual, Rev. 3
18-8 Freescale Semiconductor
Figure 18-4. MCF548x Connections to 100-pin DDR SDRAM DIMM

18.4.5 DDR SDRAM Layout Considerations

Due to the critical timing for DDR SDRAM, there are a number of considerations that should be taken into
account during PCB layout:
Minimize overall trace lengths.
Each DQS, DM, and DQ group must have identical loading and similar routing to maintain timing
integrity.
Control and clock signals are routed point-to-point.
Trace length for clock, address, and command signals should match.
Route DDR signals on layers adjacent to the ground plane.
Use a VREF plane under the SDRAM.
VREF is decoupled from both SDVDD and VSS.
To avoid crosstalk, keep address and command signals separate from data and data strobes.
Use different resistor packs for command/address and data/data strobes.
Use single series, single parallel termination (25 series, 50 parallel values are recommended,
but standard resistor packs with similar values can be substituted).
Series termination should be between the MCF548x and memory, but closest to the processor.
The parallel termination at end of the signal line (close to the SDRAM).
0.1 uF decoupling for every termination resistor pack.
MCF548X DDR SDRAM
SDADDR[12:0]
SDDATA[31:0]
SDBA[1:0]
SDCS[1:0]
RAS
CAS
SDWE
SDCKE
SDCLK[1:0]
SDCLK[1:0]
SDDM[3:0]
SDDQS[3:0]
CLK[1:0]
CLK[1:0]
CKE
S[1:0]
RAS
CAS
WE
DM[3:0]
BA[1:0]
A[12:0]
DQ[31:0]
DQS[3:0]
SCL
SDA
SCL
SDA
SA0
SDVDD