Majestic microcontroller mixup

Article By : Michael Dunn, EDN

The mother of all sub-$1 microcontroller comparisons.

I like to think of myself as the King of Cataloguing and Comparing, but I am also happy to share the glory, or in this case, completely cede it.

Reader Jay Carlson has composed a massive missive comparing 21 sub-$1 microcontrollers, and it’s glorious. Not just a simple look at chip specs, Jay dives deep into performance, and perhaps most importantly, ecosystems, devboards, and devtools. After all, any reasonably experienced engineer can get a handle on the hardware by scanning the datasheet, but the knowledge gleaned from spending a day or three with the devtools? Priceless.


Plus, this information will be applicable to higher-end processors too.

I didn’t read every word of the article, but I did notice one small item I’d like to rectify. Jay says:

Old-timers associate the 8051 with “old and slow” because the original was a 12T microcontroller — each machine cycle took 12 clock cycles to complete. Since there was no pipelining, every instruction byte took a machine cycle to fetch, plus one or more additional machine cycles to execute — altogether, it could take more than 50 clock cycles to execute a given instruction. Ouch.

I have to disagree. The 8051 was a minor miracle when it appeared in 1980. I don’t recall anyone thinking it was slow. In fact, most instructions executed in 1µs – faster than a Z-80 for the most part. Plus…hardware multiply and divide!?! In a microcontroller?!? Wow. It’s irrelevant that 12 clock cycles went by in that microsecond.

I did a “similar” comparison to Jay’s about seven years ago – though spanning a wider price range – when I needed to select a very low-end part for a very cost-sensitive project. It’s not nearly as thorough, but perhaps still of some interest.

And Jay, next time you have an idea for a project like this, get in touch! EDN would be happy to run it.

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Michael Dunn is Editor in Chief at EDN with several decades of electronic design experience in various areas.



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