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Author Topic: Determining which AVRS support external RAM  (Read 805 times)
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Evening all,

A quick pointer in the right direction please; what should I look for in an AVR's datasheet that would tell me whether or not the device supports external RAM?
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Valencia, Spain
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I think it's only the ATmega128 which can have external RAM.

Here's the datasheet: http://www.atmel.com/Images/doc2467.pdf

On page one it says "Up to 64Kbytes Optional External Memory Space", that's what to look for.
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Atmega1280/2560 as well.

Also search for "External Memory Interface" although it should be on page 1 as fungus says.

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Rob
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Rob Gray aka the GRAYnomad www.robgray.com

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An example for you to look at http://ruggedcircuits.com/html/quadram.html

These folks build rugged Arduino boards.

Paul
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Unfortunately although the SAM3 has an external memory interface the Due designers chose not to bring out one of the address lines and so IMO stuffed up royally.

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Unfortunately although the SAM3 has an external memory interface the Due designers chose not to bring out one of the address lines and so IMO stuffed up royally.

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Rob

Well they were in hurry to meet a deadline for release.  smiley-grin

Lefty
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nr Bundaberg, Australia
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smiley

One pin and they screwed external memory use. Go figure.

Maybe I should re do this

http://arduino.cc/forum/index.php/topic,129198.msg1020544.html#msg1020544

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Rob
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Quote
external RAM?
Why?  By the time you add external RAM to an Arduino, you're looking at a system cost comparable to one of the microprocessor-based boards (Beaglebone, Raspberry Pi, Xmega-A1 Xplained) that already includes RAM (typically, quite substantial amounts of RAM.  The XPlained, with 8MByte is the smallest.)
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It's easy to add SPI-bus addressable RAM to an Arduino for extra storage but if that's not suitable then you probably need to go to an ARM based board.
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Why?  By the time you add external RAM to an Arduino, you're looking at a system cost comparable to one of the microprocessor-based boards (Beaglebone, Raspberry Pi, Xmega-A1 Xplained) that already includes RAM (typically, quite substantial amounts of RAM.  The XPlained, with 8MByte is the smallest.)

I'm not adding it to an Arduino per se - but rather I've been working on my own board as part of a project for the last 3 months using an ATMega1284, but it's got to the point where I've run out of I/O (I have port expanders yes, but I can't see me activating another SPI chips' SS pin using the port expander) I'd also like more interrupts, not pin change interrupts. Changing to a larger AVR seems like a much more realistic option than throwing away the last three months and starting again. I'd also like to retain the ability to use the Arduino IDE for a while...

8 bit AVR is my first experience with micros, so I don't fancy jumping on the bandwagon of microprocessors just yet - i'll stick with controllers. Plus, I don't see the educational benefit of buying ready made hardware...

As for cost, an external RAM chip only costs a couple of £s or $s, depending which side of the ocean you're on! smiley-grin
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I can't see me activating another SPI chips' SS pin using the port expander

Why not?
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I'm already using an SPI port expander, so I'll then be accessing two SPI devices at once?
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I'm already using an SPI port expander, so I'll then be accessing two SPI devices at once?

Oh, the "port expander" is an SPI device. That would make it awkward, yes.

Still, there has to be a way to juggle it around and make it work. Can you add an extra 74HC595 or something...?




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Yep, could be a pain :-D

I'll take a look re your suggestion - but I may just stick with my current solution and look at a 32 bit chip in a later version that'll inherently have more RAM, plus CAN capability etc.
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