Revision as of 07:21, 6 May 2016

The MC14500 was a family of 1-bit task-oriented microprocessor chipsets designed by Motorola in the late 1970s intended to replace older relay-based ladder logic as a cheap programmable logic controller. Production continued well into the 1990s.

Members

Architecture

The MC14500B is a true 1-bit microprocessor - all operations are done on single-bit operands. The MC14500B comes with an internal clock that may be controlled via an external resistor. While designed to run at 1 MHz, it may be tuned down to 10 KHz or hooked up to an external clock altogether.

The MC14500B does not include any on-chip memory nor a program counter. A program counter is not provided because this MPU has no notion of memory at all, and by extension no notion of addresses. It implements an early Harvard architecture type of flow where separate instruction lines and data lines are fed to it. Individual instructions and values are fed in each clock cycle and the result can be read via a number of output lines. Typically a PROM chip such as the MCM7641 and PC such as the MC145168 were used to form a complete system. Because this was done externally, in theory at least, this MPU can support any amount of memory needed.

The MC14500B has a number of output lines to help facilitate subroutine returns, branching, conditional, and general purpose I/O. However since there are no built-in support for memory or addressing, they have to be dealt with externally, possibly with some glue chips.

ISA

Main article: MC14500 ISA

The MC14500B has a single register (the result register) and supports 16 different operations.

Documents

• Motorola MC14500B Industial Control Unit Handbook

See also

• SBA