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Rich Quinnell

32-Bit MCUs Invade 8-Bit Territory

Rich Quinnell
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Jim Turley
Jim Turley
3/28/2012 4:04:43 PM
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Re: Not just performance
That's an interesting take. The die size (i.e. silicon area) of a 32-bit MCU is small enough but the package often isn't. I wonder what the solution is. Packing a 32-bit MCU into a 6- or 8-pin package obviously means all the RAM and ROM have to be on-chip, but also most of the peripherals. Power, ground, and a couple of serial interfaces is all you'd have room for. Still... an interesting idea.

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duanebenson
duanebenson
3/28/2012 2:24:31 PM
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Not just performance
It's not just performance or cost that keeps the 8-bitters in. Packaging is a factor as well. When all other things are equal, or nearly so, form-factor comes in to play. I recently put a microcontroller into a cell-phone car charger. A six-pin MCU would have been perfect for the application. A 48-pin QFP would not have fit. Were the MCU in the original design, a tiny QFN would not have physically fit but would not have been suitable. It's an all thru-hole design (Amazing in this day but it still happens) so an eight or six pin DIP would be the order of the day. If there are any 32-bit processors in those anachronistic form factors, I'd love to hear about it and take a look at one or two.

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raimond
raimond
3/28/2012 7:29:46 AM
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Word wizard
pin compatible chips
Atmel did it some time ago. The first AVR chips were pin compatible with clasical 80C51/52 chips. The Atmega8515 still is. I used this feature once, myself. The 8515 was the perfect drop-in replacement for an 89C52.

If I will find a cortex-m chip to fit in my current ATmega8 designs for example, I will use it for sure. Of course, the designs are 5V, the chip is the "big" 0.8mm pitch QFP32 .... A lot to think about for the cortex chip manufacturers ...

The 32bitters does have some problems though, with the RAM. On the Cortex-m chips you need over 32 bytes for the stack just for starting to use the interrupts. And another 32 bytes if you have more than one level of interrupts, even if you use the two stacks system of the cortex. So I estimate that an 8K flash/1K ram atmega8 will be about 8K flash /1.5K ram cortex-m equivalent.

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northstar
northstar
3/28/2012 6:43:51 AM
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Program Manager
IAR tools
As a first signal from tools vendors, IAR is already announced support for the upcoming Freescale (and ST) chips:

http://www.marketwatch.com/story/iar-systems-supports-arm-cortex-m0-and-freescales-new-kinetis-l-series-2012-03-27-93200

One thing is for sure: supporting a single type of architecture (e.g. ARM) is easier for tools vendors.


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