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16-bit
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Sixteen digits in series.
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2s complement
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The most common method of representing negative binary numbers. If a signed bit contains a "1," all the binary digits are complemented, or reversed, and 1 is added to the number.
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8-bit
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Eight digits in series.
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addressing
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Indicating the location or priority of electrical devices through numerical systems.
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alphanumeric
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Containing letters, numbers, and special symbols found on a PLC input terminal.
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ASCII
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Short for American Standard Code for Information Interchange. ASCII was primarily used to input alphanumeric, punctuation, and control PLC characters, but has been replaced by PC keyboards.
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base 10 system
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The most commonly used number system in everyday life, also known as the decimal system. The base 10 system uses ten digits, 0-9.
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base 2 system
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The most commonly used number system in PLCs and other computer systems, also known as the binary system. The base 2 system has only two digits, 0 and 1.
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binary coded decimal
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A binary number system in which each decimal digit from 0 to 9 is represented by four binary digits (bits). The four positions have a weighted value of 1, 2, 4, and 8, ranging from right to left.
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binary system
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A numbering system that uses two digits, 0 and 1, arranged in a series of columns to represent all numerical quantities. Each column or place value has a weighted value of 1, 2, 4, 8, 16, and so on, ranging from right to left.
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bit
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A single numerical unit in the binary number system. Bit is short for BInary digiT.
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byte
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A series of eight bits.
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code
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Any system that uses digits or symbols to represent information other than simple numerical quantities. Certain code systems are used to allow a PLC to process information more efficiently or with greater accuracy.
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complement
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To reverse binary digits, with all 1s becoming 0s and all 0s becoming 1s. Complementing is a way to represent negative binary numbers.
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CPU
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Central Processing Unit. The CPU is the main device that processes information and carries out instructions in a PLC.
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decimal system
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A numbering system that uses ten digits, from 0 to 9, arranged in a series of columns to represent all numerical quantities. Each column or place value has a weighted value of 1, 10, 100, 1000, and so on, ranging from right to left.
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digit
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Any single character or symbol that is used to represent a numerical quantity.
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hexadecimal system
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A numbering system that uses 16 digits, 0 to 9 and A to F, arranged in a series of columns to represent all numerical quantities. Each column or place value has a weighted value of 1, 16, 256, 4096, and so on, ranging from right to left.
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module
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The physical connection on a PLC where an input or output is plugged in.
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multiple
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Any number that can be evenly divided by a base number, with no remainder.
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negative number
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A number representing a value less than zero. Decimals use a minus sign ( - ) to indicate negative values, but binary numbers must use 2s complement.
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nibble
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Four bits in series, or half an 8-bit byte. A nibble is used to represent decimal numbers in BCD or hexadecimal in binary.
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numbering system
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Any system using a range of digits organized in a series of columns or "places" that represents a specific quantity. The most common numbering systems are decimal, binary, octal, and hexadecimal.
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octal system
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A numbering system that uses eight digits, 0 to 7, arranged in a series of columns to represent all numerical quantities. Each column or place value has a weighted value of 1, 8, 64, 512, and so on, ranging from right to left.
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place value
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The specific column or location of a digit within a numerical system. The place value indicates the specific multiple of the numerical system's base value, or radix.
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power
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A mathematical notation indicating the number of times a quantity is multiplied by itself. Also known as an exponent.
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processor
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The part of the computer that controls the execution of program instructions.
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programmable logic controller
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A processor driven device that uses logic-based software to provide electrical control to machines.
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radix
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The base value indicating the range of digits used to represent numerical quantities in a specific numbering system. The decimal system as a radix of 10 symbols (0 through 9), and the binary system has a radix of 2 (0 and 1).
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remainder
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The quantity left over when one number is divided by another. Remainders are used to maintain whole numbers.
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signed bit
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The most significant bit of a binary number that is used to indicate whether the number is positive or negative. The signed bit must be located one place value beyond the standard set of digits.
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significant digit
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Any digit representing the greater difference between two possible numerical values. In numbering systems, the most significant digit is located farthest to the left.
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thumbwheel
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A rotary device allowing an operator to enter numerical information into a PLC. The operator selects a digit by dialing the thumbwheel.
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word
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A defined and specific number of digits grouped together. For most PLCs, a word consists of 16 digits.
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