Motorola MC14500
A one-bit CMOS microprocessor for industrial control applications.
The MC14500 Industrial Control Unit (ICU) is a CMOS one-bit microprocessor introduced by Motorola in 1977. Designed for simple control applications, it was packaged in a 16-pin DIP and normally operated at 1 MHz with 5 V, drawing only 5 μA. Its architecture is similar to that of the DEC PDP-14 computer, and it was well-suited to implementing ladder logic, allowing it to replace relay systems and programmable logic controllers.
- Manufacturer
- Motorola
- Introduced
- 1977
- Architecture
- 1-bit
- Clock speed
- 1 MHz (standard); up to 4 MHz at 15 V
- Transistor count
- Roughly 500
- Package
- 16-pin DIP
- Price
- $7.58 in 100-unit lots at launch
Lore & Background
The MC14500 was conceived by Vern Gregory in the mid-1970s while he worked as an engineer in a marketing and applications group at Motorola Semiconductor Products Sector in Phoenix, Arizona. Brian Dellande originated circuit and subroutine designs and co-wrote the manual; Ray DiSilvestro served as the bench technician, and Terry Malarkey provided management support. The chip was designed by Phil Smith in Motorola's CMOS Logic Division in Austin, Texas, where it was manufactured, with product applications support from Mike Hadley.
The processor supports 16 commands and does not include a program counter; instead, an external clock signal drives a separate PC chip, so the size of supported memory depends on that chip's implementation. The chip was still in production as of 1995. Its simplicity stemmed not only from handling 1-bit data but also from omitting internal components such as a program counter and subroutine stack, which required external chips.
Reader's Guide
The MC14500's significance lies in its role as a low-cost, low-power alternative to relay-based control systems and programmable logic controllers. Its 1-bit architecture and CMOS technology made it extremely efficient, drawing only 5 μA at 1 MHz, and it could be sped up to 4 MHz by raising the voltage to 15 V. The processor's design influenced a custom automotive chip made for Nippon Denso by Motorola in Japan. A clone, the βP14500, was manufactured by I.P.R.S. Băneasa using IIL technology rather than the original CMOS.
Notable uses include the educational WDR 1-bit computer, which featured 512 bits of RAM, an LED, I/O, and a keyboard. A modern retro-style implementation, the PLC14500-Nano, is certified as Open Source Hardware (PL000011), allowing anyone to learn from its design and build it freely. The MC14500 thus left a legacy as a foundational component in the development of simple, accessible computing systems for control and education.
Did You Know?
- It could run as fast as 4 MHz by increasing the voltage to 15 V.
- The chip did not include a program counter; that function required an external chip.
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