Electronic – How to add memory to an ARM Cortex Microcontroller

This really depends on the chips you are using - you didn't specify which one you got. Typically you would need at least a crystal, decoupling caps and reset logic. The programming interface might be a simple JTAG interface.

But all of this should be stated in the chips data sheet.

Update (for the STM32F407):

Look at the following pages in the data sheet

• 23ff. for the needed voltages (1.8-3.6V, so you need a regulator), and how to use the internal regulator (by pulling pin PDR_ON high)
• 69ff. for the pinouts
• 69+74 for the power supply scheme (this are the most interesting pages since they show the power supply connections and the needed capacitors)

You won't need a reset circuit (it's integrated - see page 23) or an oscillator (the integrated 16MHz oscillator is selected on startup, see page 22). So using a LQFP144 breakout board (like the one from futurlec(see bottom of page) might really be enough.

You can also look at the schematic of the STM32F4DISCOVERY board (see it's user manual, page 33. What you see there is the basic circuit - and it even contains the external crystals.

Some FAE explained this to me a few years back like this:

The process for fabricating DDR memory is a completely different one than the one used for the processing unit. Also, the average life time for a DDR2 IC or DDR3 IC or whatever DDR IC is much shorter (~ 3-5 years) than the availability for the processor (10-15 years). So even if they build this package-on-package IC they couldn't guarantee the lifetime, thus reducing their marketing point.

I know what you mean, laying out the DDR2/DDR3 interface is an error-prone task and requires some very low level software digging - I personally do not like that as well.