Nicola Cimmino's PCL14500 Nano Is a One-Bit Single-Board Computer Built Atop Motorola's MC14500 ICU
An oddity of 1970s programmable logic hardware can now be yours — complete with a 126-page programmers' guide.
Software engineer and vintage computing enthusiast Nicola Cimmino has designed a single-board computer designed around the classic Motorola MC14500 single-bit industrial control unit (ICU) chip: the PLC14500 Nano.
"The PLC14500 Nano is a retro-style trainer board intended for the user to familiarize with the Motorola MC14500 1-bit ICU (Industrial Control Unit), PLCs [Programmable Logic Controllers], and Ladder Logic," Cimmino explains. "The board has abundant LEDs that show the status of the system buses and registers. This, combined with the possibility to run the software step by step, gives the user a great deal of insight into how their programs are executing. The slow clock mode makes instead for a mesmerizing light show that won't fail to impress when the board is parked on a desk, waiting for the next coding adventure."
Launched by Motorola in 1976 the MC14500 appears at first glance to be a considerable step backwards compared to rival Intel's 4004 from five years earlier, given that it offers only a single bit to the 4004's four. Motorola didn't position the part as a microprocessor, though, but as an industrial control unit (ICU) — promising a low-cost low-power device for logic-based decision-making in embedded and industrial control systems.
In the PLC14500 Nano, Motorola's MC14500 is linked to 256 bytes of program RAM, replaceable with an EEPROM if you want to fix a program in-place, and offers seven momentary- and toggle-switch capable inputs and seven LEDs as outputs. There's a timer mapped to the chip's input/output (IO) bus, seven bits of "scratchpad RAM," and three clock modes: the relatively-speaking "fast," "slow," and "manual step" that allows a program to be executed clock-by-clock.
"True to its retro style PLC14500 Nano sports exclusively through-hole components and chips in DIP packages," Cimmino writes. "You might notice an intruder in the bill of materials: an Arduino Nano! It's there purely to act as a bootloader, with a convenient USB interface that surely is easy to connect to modern PCs. However, to not spoil the illusion, the Arduino is mounted on the bottom side of the PCB, so it won't be visible when using the board."
Cimmino is selling the latest revision of the PLC14500 Nano on Tindie at $39 for a bare PCB, $59 for a kit with all components, and with the option of adding his own 126-page PLC14500 Programmers' Guide book in paperback or hardback for $17.99 or $30 extra respectively. All hardware design files and source code for the project are published on GitHub under the reciprocal GNU General Public License 3.