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SDRAM memory width with Atmel AT91RM9200

Started by Stephen Jones December 7, 2004
We are designing a microcomputer based on the Atmel AT91RM9200
controller. We are gong to give it 128Mb of SDRAM, 4M X 32. I am
trying to decide whether to use 2 x 4M x 16 or 1 x 4M x 32. The
reference design uses 16 bit wide memories, which appear to be
slightly cheaper than the equivalent 32 with perhaps more
manufactureres. What do people feel, what are the advantages of each,
easier layout, better EMC, lower bus capacitance for a single chip ? I
am also looking at the option of adding two Ethernet ports but as yet
haven't worked out how to do it as it only has one MAC, could anyone
help?
Thanks


Steve Jones
> We are designing a microcomputer based on the Atmel AT91RM9200 > controller. We are gong to give it 128Mb of SDRAM, 4M X 32. I am > trying to decide whether to use 2 x 4M x 16 or 1 x 4M x 32. The > reference design uses 16 bit wide memories, which appear to be > slightly cheaper than the equivalent 32 with perhaps more > manufactureres. What do people feel, what are the advantages of each, > easier layout, better EMC, lower bus capacitance for a single chip ? I > am also looking at the option of adding two Ethernet ports but as yet > haven't worked out how to do it as it only has one MAC, could anyone > help? > Thanks
Using a single SDRAM chip reduces size, and capacitance on the adress bus, reducing power. Routing may be less complex but this is unclear. Using serial flash (Dataflash) will remove capacitance on the databus as well. External Ethernet is not so high cost. SMC91 seems to be popular in the Linux community. The alternatives I guess are to have an external three or four port switch but this is possibly more expensive. Yet another alternative is to use a USB <->Ethernet device, but throughput should be quite limited. -- Best Regards Ulf at atmel dot com These comments are intended to be my own opinion and they may, or may not be shared by my employer, Atmel Sweden.