Motorola MC14500

The MC 14500 Industrial Control Unit (ICU) is a CMOS one-bit microprocessor designed by Motorola for simple control applications in 1977.¹ It was packaged in a 16-pin DIP and normally ran at 1 MHz with 5 V and only 5 μA. If higher performance was needed, it could run as fast as 4 MHz by increasing the voltage to 15 V. It was inexpensive for the era, available at launch for $7.58 in 100-unit lots.²

MC14500B (ICU) is well-suited to the implementation of ladder logic, and thus could be used to replace relay systems and programmable logic controllers, also intended for serial data manipulation.³ The processor supports 16 commands, operating at a frequency of 1 MHz.³ The MC14500B unit does not include a program counter (PC); instead, a clock signal drives a separate PC chip; therefore the size of supported memory is dependent on the implementation of that chip. It was still in production in 1995.³

The ICU architecture is similar to that of the DEC PDP-14 computer.

The MC14500B was implemented with a transistor count of roughly 500 transistors. The chip was so simple not only because it only handled 1-bit computing data at a time, but also because the chip did not include a program counter, subroutine stack, etc. -- those required external chips.⁴

The ICU was conceived by Vern Gregory in the mid-1970s while working as an engineer in a marketing / applications group of Motorola Semiconductor Products Sector in Phoenix, Arizona, USA; Brian Dellande originated circuit and sub-routine designs, and co-wrote the manual; Ray DiSilvestro was the bench technician; Terry Malarkey provided management support.

In the CMOS Logic Division in Austin, Texas, USA (where it was made) Phil Smith was the chip designer; Mike Hadley provided product applications support.

A form of the design served as an embedded controller in a custom automotive chip made for Nippon Denso by Motorola—Japan.

I.P.R.S. Băneasa manufactured a clone of the MC14500B with the designation βP14500 in IIL technology (rather than the original CMOS).⁵

One of the computers known to be based on this processor is the educational WDR 1-bit computer (512 bits of RAM, LED, I/O, keyboard).⁶

A modern take, in retro style, of a computer based on this processor is the PLC14500-Nano. It is certified as Open Source Hardware PL000011 so anyone can learn from its design and can freely build it.