As a followup of my clock kit, I’m growing a genuine interest into the 8051. While more modern MCU are vastly more powerful, the 8051 is just barely as complex as needed to be useful. That’s a sweet spot that makes it invaluable for learning purposes.

It is more on the verge of retroputing1, but I’m more on the side that one should learn simple things first, even if long past due date.

It always helped me to have the full process of invention. Every step is obvious in retrospect, and I can remember much more easily.

Programming should be done in logic gates first, then assembly, then higher and higher. Starting with Stratch is a nonsense. That said, if it makes younger people interested in programming, I can see its usefulness. Just not for the learning part.

Simplicity is everything

That said, there is a very interesting trait in looking into very simple things. And the 8051, simple, it is.

Nowadays, in that 8051 family, there’s a lot of diversity. As said elsewhere, the 8051 will not be extinct soon.

I also think that the AT89C2051 hits the very sweet spot for hobbyists. Its rather small DIP-20 form factor makes it super easy to insert to almost any design. And while its more recent editions versions (AT89S2051 & AT89LP2052) are much faster (1T instead of 12T) and have more features, they are much more expensive.

Having less features makes it also easier to learn. As one has to revert to more creative ways. It is even possible to use multiple MCU to achieve what we want, leaning into the world of multi-chip computing.

In addition, the fact that the AT89C2051 is used is almost every cheap DIY clock kit is a guarantee of very cheap availability, because it give incentives to provide clones that are binary compatible, if not recycling original chips from obsolete hardware.

Funnily, each clock model I encountered has a different chip signature2, whereas the markings are looking like the original AT89C2051. I didn’t detect any other issue with them. But are obviously fakes.

The only real pain point for the AT89C2051 is the 12V high-voltage requirement for its programming, as it needs a HVPP3. Which I have solved in my previous post.


Now, as I’m learning about the architecture, relying on programming/test/reprog/retest cycles only goes for a while.

As there is no debugging tool on the hardware part, I searched for an emulator. Here also, the fact that the 8051 is a standard part (such as NE555) makes those plentiful.

I selected emu8051 from Jari Komppa which did not require any libraries outside ncurses. The others being too cumbersome. I love the terminal, but a visual UI is still a must.

The fact that the code wasn’t very optimized for speed, but more for readability and accuracy was the decisive factor.

I implemented a rustic TX serial to be able to easily see what was sent.

  1. Contraction of “Retro Computing” 

  2. for example 1C 20 instead of the official 1E 21 

  3. High Voltage Parallel Programmer