A one-bit processor explained: the vintage MC14500B #VintageComputing @kenshirriff

The Motorola MC14500B is a 1-bit processor introduced in 1976. While a 1-bit processor might seem almost useless, it was marketed as an Industrial Control Unit for applications that made simple decisions based on Boolean logic, for example, air conditioning, motor control, or traffic lights.

Ken Shirriff discusses reverse engineering this classic chip.

The MC14500B has an unusual architecture, making it more of a building block than a complete microprocessor. In particular, the chip doesn’t include any support for memory or addresses; it didn’t even have a program counter. The program counter, instruction fetches, jumps, subroutine calls, and I/O needed to be implemented with external circuitry. This is a key reason that the chip was so simple. (The other reason, of course, was that it only supported one bit.)

Since the MC14500B was designed for industrial control applications, you’d expect it to be a microcontroller, but it’s the opposite of a microcontroller in many ways. A typical microcontroller is a computer-on-a-chip including RAM and ROM, with strong I/O support, providing a single-chip solution. The MC14500B, however, requires multiple external chips to make it usable.

Read the full details on Ken’s blog here.


Have an amazing project to share? The Electronics Show and Tell is every Wednesday at 7:30pm ET! To join, head over to YouTube and check out the show’s live chat and our Discord!

Join us every Wednesday night at 8pm ET for Ask an Engineer!

Join over 38,000+ makers on Adafruit’s Discord channels and be part of the community! http://adafru.it/discord

CircuitPython – The easiest way to program microcontrollers – CircuitPython.org


New Products – Adafruit Industries – Makers, hackers, artists, designers and engineers! — New Products 11/15/2024 Featuring Adafruit bq25185 USB / DC / Solar Charger with 3.3V Buck Board! (Video)

Python for Microcontrollers – Adafruit Daily — Python on Microcontrollers Newsletter: A New Arduino MicroPython Package Manager, How-Tos and Much More! #CircuitPython #Python #micropython @ThePSF @Raspberry_Pi

EYE on NPI – Adafruit Daily — EYE on NPI Maxim’s Himalaya uSLIC Step-Down Power Module #EyeOnNPI @maximintegrated @digikey

Adafruit IoT Monthly — The 2024 Recap Issue!

Maker Business – Adafruit Daily — Apple to build another chip at TSMC Arizona

Electronics – Adafruit Daily — SMT Tip – Stop moving around!

Get the only spam-free daily newsletter about wearables, running a "maker business", electronic tips and more! Subscribe at AdafruitDaily.com !


1 Comment

  1. Steampunk Professor

    We used these as part of our electronics unit when I did my Phystcs degree back in the mists of time. They were a fun introduction to the nitty gritty of microcontrollers.

Sorry, the comment form is closed at this time.