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July 17, 2002
68
SDR Memory Design
The critical timing parameters of the processor memory controller and SDR SDRAM devices are shown in
Table 13. The design rules described in this document satisfy these timings.
Careful placement and routing of the SSDR DRAM interface signals results in the best possible memory
performance. Trace lengths can be controlled and clock feedback delays correctly calculated. If provision is
made to compensate for layout and timing uncertainties with zero
Ω
resistors, it is possible to attain PC133
data rates on TM5500/TM5800 processor-based system designs.
5.3.2 Example Design Strategy
Layout of the TM5500/TM5800 processor SDR SDRAM interface is simplified with the application of one
basic strategy:
Laying out the SDR SDRAM design using only JEDEC-compliant SODIMMs is very straightforward. Place the
SODIMMs close together, using reverse-image connectors, routing signals from the processor to the
SODIMMs.
Note that if the SODIMM connectors are placed in close proximity, it does not matter whether a star or daisy-
chain topology is used.
If the SDR SDRAM memory is laid out in this way, the system has the best possible performance, as long as
the read and write timings are carefully controlled.
Table 13:
SDR SDRAM Interface Device Specifications
Device
Output Hold Time
Input Setup Time
Input Hold Time
TM5500/TM5800 (800 MHz SKU)
1
1.
The figures listed here are examples only. See the
Data Book
for processor memory timing
specifications.
1.38-1.96 nS
1.7 nS
1.9 nS
JEDEC-compliant SDRAM
2.2-5.0 nS
1.5 nS
0.8 nS
Critical Rule
The TM5500/TM5800 processor SDR SDRAM layout works optimally with SODIMMs, specifically JEDEC-
compliant SODIMMs.
Figure 10:
Physical SDRAM Configurations
CPU
SODIMM 0
SODIMM 1
CPU
Содержание Crusoe TM5500
Страница 1: ...TM5500 TM5800 System Design Guide July 17 2002...
Страница 6: ...July 17 2002 6 List of Tables...
Страница 8: ...July 17 2002 8 List of Figures...
Страница 50: ...July 17 2002 50 Processor Power Supplies and Power Management...
Страница 110: ...July 17 2002 110 System Design Considerations...
Страница 122: ...July 17 2002 122 System Design Checklists...
Страница 128: ...July 17 2002 128 Serial Write protection PLD Data...
Страница 130: ...July 17 2002 130 Index...