ALU of the Day: Motorola MC14581CL – Logic 4 bits at a time
Motorola MC14581CL 4-bit ALU – 1973
At the heart of every processor is an ALU, an Arithmetic Logic Unit. It is what does the addition, subtraction, compares, and other logic function on the bits we call data. Add some memory for registers, stack, and program control and one has a basic processor, or bit slice processor. In the 1970’s and even the 1980’s many systems still implemented their ‘processor’ in discrete logic. The 74181 (TTL), 10181 (ECL) and 14581 (CMOS) were the heart of many of them. The ‘181 could handle any of 16 arithmetic and logic functions on a pair of 4 bit words.
The Motorola MC14581CL was the first of the CMOS ALU’s. This example was made in early 1973. CMOS itself was only patented a few years prior (1967) and didn’t see extensive use in processors until the mid 1970’s (RCA 1802) and most other processors in the 1980’s. Remarkably, after 40 years, its still in its original package.
