Minimal ARM circuit requirements

Question

I have done some development with the ATMega and I'm looking to broaden my horizons. I have a couple Cortex M4 series chips and would like make an ARM equivalent to the Breadboarduino

I plan to either etch my own board or use a breakout board for the ARM and breadboard the rest. A reference or schematic of the minimum components would be greatly appreciated.

Are there any good resources for determining the minimum required components to operate, and ideally program, an ARM chip?

UPDATE:

I'm open to alternative hardware suggestions. Below is the chip that I'm currently trying to work with:

• STM32F407ZGT6
• Datasheet

Answer 1

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.

Answer 2

Are you sure you want to do this for a Cortex-M4? It's a big leap from AVR, and I don't see how you would make use of all the features it provides. To start with a Cortex-M4 usually comes in a large package, typically more than 80 pins for the entry level parts, and 200+ is not an exception, think QFP or BGA. Are going to make a breakout board with two rows of 40 pins to breadboard?

The Cortex-M4 is also designed for high-speed: 120 MHz to 200+ MHz typically. OK, you may not need to design your PCB for those speeds if you use an on-chip PLL. But what about the peripherals, like USB or Ethernet?

Of course you can run it at lower speeds, and leave out much of the on-chip functionality, but I wonder what's the use of a Cortex-M4 to start with. I think a Cortex-M3 or even -M0 is more appropriate to start with. I don't want to discourage you, I want to remain realistic.

If you do want to go ahead with the Cortex-M4 you can do with minimal external hardware. The NXP LPC407x for instance has an internal RC-oscillator which is the default oscillator at reset, so you don't even need a crystal. A reset circuit and proper power supply decoupling will be all you need to get it up and running.

For a Cortex-M0 the NXP LPC111x may be worth having a look at. Granted, it doesn't come with lots of memory, but it's available in a DIL-28 package, which is a rarity for ARMs. Alternatively you can use a development board like the LPCXpresso,

where the right half is the application board, which can be separated from the LPC-link. As you can see there's hardly any external hardware required for the application. And if you solder a set of headers on it you can plug it onto a breadboard.

Answer 3

As Steven says it's quite a big leap to ARM from an 8-bit micro, so expect a fair bit of learning/time spent on the way.
I also wouldn't go for the M4 for your first ARM, simply because it hasn't be out too long and there is less support/info out there for it. I think an M3 or M0 is a better choice, and will be plenty to be getting on with.

You can certainly make your own board, but it would maybe be better to grab a small/cheap dev board first. Development wise, there are lots of options, from free (eclipse + GCC + OpenOCD) to expensive (Keil, Rowley, etc) Personally I use the Raisonance Ride7 IDE and tools with the STM32 series ARM M3/M4s, which is a bit cheaper than Keil/Rowely but good enough.

Have a look at one of the simple dev boards from someone like ST, Olimex, etc. This dev board has about the simplest schematic I could find, for an STM32 Cortex-M3.

Answer 4

The Arduino Due should be out fairly soon:

Chip is a SAM3X8 Cortex-M3 from Atmel. Might be worth the wait if you're already familiar with Arduino style boards and Atmel style documentation. And since it will be open source to satisfy the Arduino requirements, you could of course breadboard-duino it.

Answer 5

I would recommend you check Mbed its a cortex-m3 device with a few nice peripherals, nxp provides compiler and lots of library and community libraries, a really easy way to program it and its already in a package to be used on a breadboard. I think it would be the easiest way to transition from AVR to ARM.

Answer 6

Many of the ST parts can, at least if not using a USB transceiver, run off their internal high speed oscillator.

That basically means your "circuit" consists of bypass caps and a few resistors on things like the reset and as termination on the SWD interface.

ST's $8-10 eval boards will program parts you put on your own board over the SWD bus; there are open source tools for them too, so you can put the programming operation right in your Makefile.

Going for something in the 48 PQFP probably will make life easier on your first board attempt. You can assembly these without magnification (just have fine braid available to fix the bridge or two you will probably create per side), but having a loupe available to check your work would be helpful.