The MC14500B Industrial Control Unit (ICU) is a CMOS one-bit microprocessor designed by Motorola for simple control applications in 1977. It 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. The processor supports 16 commands, operating at a frequency of 1 MHz. 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.
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, AZ; 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, TX (where it was made) Phil Smith was the chip designer; Mike Hadley provided Product Applications support.
The ICU was a steady seller for 20+ years. As of 2018, it is still available on the aftermarket.
A form of the design served as an embedded controller in a custom automotive chip made for NipponDenso by Motorola—Japan.
A 1-bit computer architecture is an instruction set architecture for a processor that has datapath widths and data register widths of 1 bit (1/8 octet) wide.
An example of a 1-bit computer built from discrete logic SSI chips were the Wang 700 (1968/1970) and Wang 500 (1970/1971) calculator as well as the Wang 1200 (1971/1972) word processor series of Wang Laboratories.
An example of a 1-bit architecture that was marketed as a CPU is the Motorola MC14500B Industrial Control Unit (ICU), introduced in 1977 and manufactured at least up into the mid 1990s. One of the computers known to be based on this CPU was the WDR 1-bit computer. A typical sequence of instructions from a program for a 1-bit architecture might be:
load digital input 1 into a 1-bit register;
OR the value in the 1-bit register with input 2, leaving the result in the register;
write the value in the 1-bit register to output 1.This architecture was considered superior for programs making decisions rather than performing arithmetic computations, for ladder logic as well as for serial data processing.There are also several design studies for 1-bit architectures in academia, and corresponding 1-bit logic can also be found in programming.
Other examples of 1-bit architectures are programmable logic controllers (PLCs), programmed in instruction list (IL).
Several early massively parallel computers used 1-bit architectures for the processors as well. Examples include the Goodyear MPP and the Connection Machine. By using a 1-bit architecture for the individual processors a very large array (e.g.: the Connection Machine had 65,536 processors) could be constructed with the chip technology available at the time. In this case the slow computation of a 1-bit processor was traded off against the large number of processors.
1-bit CPUs can meanwhile be considered obsolete, not many kinds have been produced and none are known to be available in the major computer component stores (as of 2019, a few MC14500B are found on eBay). The Finnish company Partco offered MC14500B as spare part in 2017.List of NXP products
The following is a partial list of NXP and Freescale Semiconductor products, including products formerly manufactured by Motorola until 2004. Note that NXP and Freescale merged in 2015.Serial computer
A serial computer is a computer typified by bit-serial architecture — i.e., internally operating on one bit or digit for each clock cycle. Machines with serial main storage devices such as acoustic or magnetostrictive delay lines and rotating magnetic devices were usually serial computers.
Serial computers required much less hardware than their parallel computing counterpart, but were much slower.