Weird memory design in M5282EVB

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Hello!

I just had a look at the manual to the motorola coldfire 5282 evb, and
I´d like to understand why they connected the sdram-chips to the
processor the way they did.

The schematics can be found at
http://e-www.motorola.com/files/soft_dev_tools/hardware_tools/printed_circuit_boards/M5282EVB-SCH.pdf

In short: They connected the chips to A9...A23. A0...A8 are not used by
sdram, but by the flash-rom, which ist connected as usual.

Any idea?

Tankred.


Re: Weird memory design in M5282EVB

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http://e-www.motorola.com/files/soft_dev_tools/hardware_tools/printed_circuit_boards/M5282EVB-SCH.pdf
Quoted text here. Click to load it
My guess is that the chip has a built in SDRAM controller, and that is the
configuration you need to wire it in for the controller to work correctly.
DRAM is address by row and column, not by decoded address.
Tony




Re: Weird memory design in M5282EVB
Yes, you are right!
I wasn´t aware that an internal memory controller doesn´t have to be
connected in the "normal" way.

Thanks for your help, today I got a bit smarter than yesterday...

Tankred.




Re: Weird memory design in M5282EVB
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It's common on uCs that share (S)DRAM and flash/SRAM controller
functions on a single address bus, to have the flash address pins
count up from one "end" of the bus and the SDRAM address lines either
to count down from the other "end" or just to be translated left some
number of bits.

I think the rationale is to cut down on the number of
pin-state-changes in interleaved flash-SDRAM access cycles, in order
to reduce EMI and perhaps improve performance in
high-capacitative-loading situations. Since it's the LSbits that will
be changing most frequently (on the flash controller anyway), it makes
sense to separate those bits from the SDRAM control bits.

Someone correct me please if this is grossly wrong and based on flawed
science...

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