Are there any current non-Harvard architecture microcontrollers?

Question

I have used and like the Atmel ATMEGA and ATTINY series microcontrollers, and think them quite good. One thing I am not terribly fond of though is the fact that they (and Microchip PIC uC family also) are all Harvard machines, meaning I can't really put external memory to use or execute out of RAM, only the flash.

While there are obvious advantages to this design, it makes it technically very difficult to do things like FORTH using an AVR or PIC. (I know there is at least one implementation, but it does not work like a normal FORTH and will wear out the flash rather rapidly)

FORTH was originally created for interactive machine control type systems where lots of flexibility was needed, so things like the Z80 or 6809 were used as microcontrollers with the control program executing out or RAM or some other storage device.

Does anyone know of current devices of similar complexity (preferably available in DIP packages) to the AVR/PIC that are von Neumman machines?

Answer 1

Farnell has a nice search function that let's you search for microcontrollers in DIP packages. Though you'll have figure out which families are non-Harvard by looking at the data sheets.

Take a look at the 68K ones and the HCS08.

Update: In the meantime some ARM Cortex-M controllers in DIP packages have become available, the LPC810M021FN8 and the LPC1114FN28 from NXP.

Answer 2

In addition to Freescale processors (that starblue has already pointed out), the Texas Instrument MSP430 family uses von Neumann architecture. However only the smallest ones are available in a DIP package.

UPDATE to include PIC32:

In my original post, I had forgotten that PIC32 microcontrollers have always been able to execute out of RAM, as demonstrated by this code example;and now Microchip has come out with the new PIC32MZ line of microcontrollers, with up to 2 MB of Flash and 512K of RAM which makes them feasible for fairly large RAM-based programs. Unfortunately none of them chips are available in DIP packages.

However Olimex, sort of the Bulgarian equivalent of SparkFun and Adafruit, has a PIC32-HMZ144 development board for $21.95 EUR, which is about $24. This is a smoking hot deal since the processor alone costs over $12 at Digi-Key. (There are other boards available from US suppliers from around $50 and up.)

The original PIC32MX line has twenty variants in 28-pin DIP packages, but they are limited to a maximum of 64K of RAM, still useful for some projects.

Answer 3

You might want to peruse the designs available at the OpenCores project. That is an open source project devoted to CPU core designs implemented in VHDL, Verilog, and similar FPGA design languages. There are complete and respectable implementations of classic 8-bit CPUs such as the 8080, 6502, and 8051. The 6502 I linked to claims to be cycle-accurate compared to the original chip. Others are functionally complete, but often have more modern buses and signals.

They won't (I think) be available in DIP packages, but you can always find breakout boards.

The designs are all open source, under a wide variety of licenses.

Answer 4

The arm based ones, even the cortex-m3 claims to be harvard, but you can load programs into data ram and execute from that ram. it is really not harvard. Other arms are normally not harvard, some have external memory interfaces you can use to expand the internal resources.

Answer 5

This is actually not a question, but more of a related query. Why would you go to von-neumann in a microcontroller if the previous generation was harvard? Isnt it all win-win in terms of performance? other than complexity (which if the original PIC's can handle it, should not be that great) what are the downsides of having Harvard architecture?

Answer 6

You may also have a look at the Zilog eZ80. Since they're binary-compatible with the old Z80, you should be able find a FORTH implementation that runs on them, but you'd probably need to run it on top of good old CP/M :)

Also, these are the only ones that I found that have the memory bus accessible from the outside, i.e. allow code execution from external memory.

Answer 7

The new Kinetis line of microcontrollers from Freescale puts an ARM Cortex-M4 inside a microcontroller package, and program code can be located anywhere in addressable space (RAM or FLASH, or even Flex Memory.)

The Kinetis Solution Advisor is a powerful selector guide that can help you find the micro you want. Memory from 32kB to 1MB, all the peripherals you could want, and pricing from under a dollar to around 10.