Large external RAM

[baris_togrul]

Posted on April 30, 2012 at 00:58

Hi guys.I have been playing with Stm32f4 discovery for couple months.

My problem follows like this;I have to take 2 vga images from CMOS camera and store them.I will make some mathematical operations on both images.And this system will work all day long.That's way i cant use flash memory(due to read-write cycle is not infinite,at least i know it like that).2 vga images (raw RGB coded) occupies about 4MB.So i checked ebay and some other sites but i could not find any proper ram.digikey has some but their ram packages not solderable by hand 🙂 What should i do? What if i use flash memory instead of ram?Or what kind of ram can be found ?

[Tesla DeLorean]

Posted on April 30, 2012 at 04:35

Flash is going to be totally useless for the bandwidth you need. Aside from the life cycles, the stuff is SLOW, and you have a lot of data.

If you can solder TSOP 48 packages, then perhaps the CY62177E will work for you. If the packaging is unsuitable for your soldering skills, then you're going to have to pick some lower density parts, and use multiple devices, or frankly consider using a micro-controller that can use SDRAM. The industry is moving to denser and smaller parts using tight pitch BGA's, you'll need to embrace these form factors if you expect to find mass volume parts. ie utilized in phones, tablets, notebooks, PCs, etc.

[baris_togrul]

Posted on May 01, 2012 at 22:09

Thanks for quick reply.I checked them but it seems quite expensive(35 bucks for each) I think i will use QVGA for this case.Can you offer MCU with SDRAM controller? And can i use pc133 DIMM rams?

[Tesla DeLorean]

Posted on May 01, 2012 at 23:27

Cost is a factor of using a niche part, DigiKey is always about twice as expensive as dealing with the mfg directly. The semi mfgs are moving to built-to-order, with long delivery times, and killing older lines and unprofitable products.

DIMMs aren't something typically seen on embedded micros, except perhaps some eval boards, you could look at some embedded PC boards. Embedded micro's tend to utilize a handful of SDRAM chips, tightly coupled. The kind of pin counts needed to interface to a DIMM gets you back to your packaging issue, the routing of a PCB is also significantly challenging for 100-133+ MHz signals. The chips on the DIMMs are often just 16-bit wide SDRAM's, Micron offers these as 100 or 133 MHz in TSOP packages. When you get to DDR2 or DDR3 you're back in BGA land. You could take a look at ST's older SPEAr parts, problematic because of the BGA, but mentioned because it's their site. I'd look at some FreeScale ColdFire or Kinetis, NXP LPC32xx, or ATMEL AT91SAM9xxx parts. I'd go dig but you have some tight cost and packaging limitations. You're basically going to be looking at ARM9 devices, capable of running WinCE or Linux, at perhaps 200-400 MHz, for older tech that was built in enough volume to be lower cost, and still available. Most of this market is now chasing ARM A9 designs in phones and tablets.