Electronics > Microcontrollers

Using PC RAM with microcontrollers

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NiHaoMike:
Recently, I managed to get a bag of old RAM for free. It had a few 30 pin and 72 pin SIMMs, lots of SDRAM and DDR DIMMs, and even a few small DDR2 DIMMs. Since none of them are usable (or worth using) in a modern PC, is it possible to use them with high end microcontrollers like a PIC24/dsPIC or ARM M4?

mikeselectricstuff:
Forget DDR2 or later as they tend to have PLL clocks that require a minimum clock rate.
Standard SDRAM (unbuffered) can be interfaced fairly easily, either using onboard memory controllers on some of the higher end ARMs etc., or (slowly) via I/O ports.
If you want good info on the protocols check the Micron website - their datasheets are very clear and comprehensive.
SDRAM is also very easy to interface to FPGAs.

johnmx:
DRAM memories need a special controller to continuously refresh the memory cells. My guess is that this type of memory is not good for microcontrollers. SRAM type doesn’t have this problem.

mikeselectricstuff:

--- Quote from: johnmx on November 06, 2011, 09:26:26 pm ---DRAM memories need a special controller to continuously refresh the memory cells. My guess is that this type of memory is not good for microcontrollers. SRAM type doesn’t have this problem.

--- End quote ---
If you can access the  RAM at reasonable speed, then refresh is a relatively easy task.

Psi:
You won't be able to use external ram to extend the micros built in ram in order to have more variables etc.  unless external ram is a special feature of that micro.

But you can wire up the sram and write some code to read/write it yourself.

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