Final answer:
The missing numbering system commonly used by PLCs is hexadecimal, which joins decimal, binary, octal, and binary coded decimal as the primary systems for representing numbers in PLC programming.
Step-by-step explanation:
The five numbering systems commonly used by PLCs (Programmable Logic Controllers) are hexadecimal, decimal, binary, octal, and binary coded decimal (BCD). In the world of PLCs and computing in general, numbers form the basis of data and instructions handling.
The numbering systems each have a unique base and set of permissible digits. For example, decimal numbers are based on ten digits (0 through 9), and when digits are written in a row, such as 123, without a marked decimal point, it is understood to be on the right end of the number, signifying 123.0. The binary system uses base 2 and includes only the digits 0 and 1.
The octal system is base 8, using the digits 0 through 7. Hexadecimal is base 16, which includes the decimal digits plus six additional symbols, often represented as A through F or a through f, with each symbol representing values ten through fifteen respectively. Lastly, binary coded decimal is a system where each decimal digit is represented by its fixed number of four binary digits.