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.

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.

Answer 3

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 4

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.