The Holtek HT68F001: 16 Byes of RAM, 32kHz microcontroller at ~10-cents
holtek.com
holtek.com
Holtek makes a lot of esoteric parts, such as the IC for musical greeting cards.
Resource wise these are around 8048 or 1802 style programming. The kind of stuff I love to do.
Some projects just can't afford heavy resource parts. The Toy Industry for one.
EM Microelectronics also makes LOW end parts. 4-Bit parts are still a thing.
https://www.emmicroelectronic.com/product?title=&term_node_t...
The Preface to Murphy's Law:
We, the willing, .Lead by the unknowing. ..Are doing the impossible for the ungrateful. ...We have done so much for so long, ....With so little, .....We are now qualified to do anything, ......With nothing, .......Forever!
I did a brief search before posting, and one webpage suggested a 1000+ quantity price for $0.11 USD. However, upon closer inspection, this webpage is completely out-of-stock. (https://www.lcsc.com/product-detail/Others_Holtek-Semicon-HT...). I assumed the ~10-cent price point was still available and should have looked more into it before posting.
> Holtek 'Buy Online' shows $1.50 @ 500+
That is indeed terrible. ATTiny4 chips (cheapest chip on Digikey that's available... 512B Flash + 32B RAM) are available at 39-cents @100 Quantity from Digikey, so these HT68F001 chips need to come in significantly cheaper than the ATTiny4 before I consider them.
Sure, the ATTiny4 is like 20 uA at 128kHz, but this is all less than the leakage current of batteries, so we're definitely looking at multi-year battery lives. Also PWM, Analog Comparator, ADCs, and other such features are included. So its more capable.
In 2019, the HT68F001 _WAS_ a 8.75-cent chip or so. Alas, the 2020+ chip shortage may have killed the cost-effectiveness of this particular model.
Notes:
1. 512 12-bit words of Flash (12-bits per instruction).
2. Designed to be programmed directly in assembly.
3. 32kHz internal clock. When powered with 1.8V, the device is specified with 3.0 uA maximum current, and 1.5uA typical current. For reference, a 3000mA-hr AA battery with 15-year life span has ~22uA leakage current.
4. If that wasn't enough, the chip does have a "HALT" instruction, setting the processor into a sleep mode that further drops power consumption down.
5. All instructions require at least 4-clocks to execute. So this 32kHz CPU only executes 8 kilo-instructions per second... and some instructions require 2 cycles... meaning 4-kilo-instructions per second worst case.
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We programmers often forget how "small" the world of microcontrollers can get. Tiny chips, like this HT68F001 serve to remind us how small practical programs can be in the real world.
Despite the hilariously poor specs of this uC (even by other uC standards), the power-consumption specs are absolutely spectacular. Its difficult for me to think of a rival chip that can dome down to 3uA worst-case specified current consumption at 1.8V. (A lot of the "low power uCs", like STM32U5, cheat by using a buck-converter and write their specifications against 3.3V).
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By cutting clock speeds to the lowest reasonable speeds: these kinds of uCs allow the programmer to check on values thousands-of-times per second and react within microseconds to various events automatically.
And they do so while using the absolute lowest amounts of power possible.
That being said, communications will become an issue. An 8kHz uC without a UART will not even be able to communicate over 9600 Baud UARTs (aka: 9.6kHz communication speed), though bit-banging a signal out at 300 Baud might still be possible.