Binary | Gray code | One-hot |
---|---|---|

000 | 000 | 00000001 |

001 | 001 | 00000010 |

010 | 011 | 00000100 |

011 | 010 | 00001000 |

100 | 110 | 00010000 |

101 | 111 | 00100000 |

110 | 101 | 01000000 |

111 | 100 | 10000000 |

In digital circuits and machine learning, a **one-hot** is a group of bits among which the legal combinations of values are only those with a single high (1) bit and all the others low (0).^{ [1] } A similar implementation in which all bits are '1' except one '0' is sometimes called **one-cold**.^{ [2] } In statistics, dummy variables represent a similar technique for representing categorical data.

One-hot encoding is often used for indicating the state of a state machine. When using binary or Gray code, a decoder is needed to determine the state. A one-hot state machine, however, does not need a decoder as the state machine is in the *n*th state if and only if the *n*th bit is high.

A ring counter with 15 sequentially ordered states is an example of a state machine. A 'one-hot' implementation would have 15 flip flops chained in series with the Q output of each flip flop connected to the D input of the next and the D input of the first flip flop connected to the Q output of the 15th flip flop. The first flip flop in the chain represents the first state, the second represents the second state, and so on to the 15th flip flop which represents the last state. Upon reset of the state machine all of the flip flops are reset to '0' except the first in the chain which is set to '1'. The next clock edge arriving at the flip flops advances the one 'hot' bit to the second flip flop. The 'hot' bit advances in this way until the 15th state, after which the state machine returns to the first state.

An address decoder converts from binary or Gray code to one-hot representation. A priority encoder converts from one-hot representation to binary or Gray code.

In natural language processing, a one-hot vector is a 1 × *N* matrix (vector) used to distinguish each word in a vocabulary from every other word in the vocabulary. The vector consists of 0s in all cells with the exception of a single 1 in a cell used uniquely to identify the word. One-hot encoding ensures that machine learning does not assume that higher numbers are more important. For example, the value '8' is bigger than the value '1', but that does not make '8' more important than '1'. The same is true for words: the value 'New York' is not more important than 'York'.

- Determining the state has a low and constant cost of accessing one flip-flop
- Changing the state has the constant cost of accessing two flip-flops
- Easy to design and modify
- Easy to detect illegal states
- Takes advantage of an FPGA's abundant flip-flops

Using a one-hot implementation typically allows a state machine to run at a faster clock rate than any other encoding of that state machine.^{ [3] }

- Requires more flip-flops than other encodings, making it impractical for PAL devices
- Many of the states are illegal
^{ [4] }

The **bit** is a basic unit of information in information theory, computing, and digital communications. The name is a portmanteau of *binary digit*.

In computing and electronic systems, **binary-coded decimal** (**BCD**) is a class of binary encodings of decimal numbers where each digit is represented by a fixed number of bits, usually four or eight. Sometimes, special bit patterns are used for a sign or other indications.

In digital logic and computing, a **counter** is a device which stores the number of times a particular event or process has occurred, often in relationship to a clock. The most common type is a sequential digital logic circuit with an input line called the *clock* and multiple output lines. The values on the output lines represent a number in the binary or BCD number system. Each pulse applied to the clock input increments or decrements the number in the counter.

In mathematics and computing, **hexadecimal** is a positional system that represents numbers using a base of 16. Unlike the common way of representing numbers with ten symbols, it uses sixteen distinct symbols, most often the symbols "0"–"9" to represent values zero to nine, and "A"–"F" to represent values ten to fifteen.

In digital circuits, a **shift register** is a cascade of flip flops, sharing the same clock, in which the output of each flip-flop is connected to the "data" input of the next flip-flop in the chain, resulting in a circuit that shifts by one position the "bit array" stored in it, "shifting in" the data present at its input and 'shifting out' the last bit in the array, at each transition of the clock input.

**VHDL** is a hardware description language used in electronic design automation to describe digital and mixed-signal systems such as field-programmable gate arrays and integrated circuits. VHDL can also be used as a general-purpose parallel programming language.

The **reflected binary code** (**RBC**), also known just as **reflected binary** (**RB**) or **Gray code** after Frank Gray, is an ordering of the binary numeral system such that two successive values differ in only one bit.

In computing, a **linear-feedback shift register** (**LFSR**) is a shift register whose input bit is a linear function of its previous state.

**Verilog**, standardized as **IEEE 1364**, is a hardware description language (HDL) used to model electronic systems. It is most commonly used in the design and verification of digital circuits at the register-transfer level of abstraction. It is also used in the verification of analog circuits and mixed-signal circuits, as well as in the design of genetic circuits. In 2009, the Verilog standard was merged into the SystemVerilog standard, creating IEEE Standard 1800-2009. Since then, Verilog is officially part of the SystemVerilog language. The current version is IEEE standard 1800-2017.

In digital electronics, a **binary decoder** is a combinational logic circuit that converts binary information from the n coded inputs to a maximum of 2^{n} unique outputs. They are used in a wide variety of applications, including data multiplexing and data demultiplexing, seven segment displays, and as address decoders for memory and port-mapped I/O.

The **Lempel–Ziv–Markov chain algorithm** (**LZMA**) is an algorithm used to perform lossless data compression. It has been under development since either 1996 or 1998 by Igor Pavlov and was first used in the 7z format of the 7-Zip archiver. This algorithm uses a dictionary compression scheme somewhat similar to the LZ77 algorithm published by Abraham Lempel and Jacob Ziv in 1977 and features a high compression ratio and a variable compression-dictionary size, while still maintaining decompression speed similar to other commonly used compression algorithms.

**Excess-3**, **3-excess** or **10-excess-3** binary code, **shifted binary** or **Stibitz code** is a self-complementary binary-coded decimal (BCD) code and numeral system. It is a biased representation. Excess-3 code was used on some older computers as well as in cash registers and hand-held portable electronic calculators of the 1970s, among other uses.

**Binary data** is data whose unit can take on only two possible states, traditionally labeled as 0 and 1 in accordance with the binary numeral system and Boolean algebra.

**PicoBlaze** is the designation of a series of three free soft processor cores from Xilinx for use in their FPGA and CPLD products. They are based on an 8-bit RISC architecture and can reach speeds up to 100 MIPS on the Virtex 4 FPGA's family. The processors have an 8-bit address and data port for access to a wide range of peripherals. The license of the cores allows their free use, albeit only on Xilinx devices, and they come with development tools. Third party tools are available from Mediatronix and others. Also PacoBlaze, a behavioral and device independent implementation of the cores exists and is released under the BSD License. The PauloBlaze is an open source VHDL implementation under the Apache License.

A **ring counter** is a type of counter composed of flip-flops connected into a shift register, with the output of the last flip-flop fed to the input of the first, making a "circular" or "ring" structure.

**Densely packed decimal** (**DPD**) is an efficient method for binary encoding decimal digits.

A **canonical Huffman code** is a particular type of Huffman code with unique properties which allow it to be described in a very compact manner.

In cryptography, **Mutual Irregular Clocking KEYstream generator (MICKEY)** is a stream cipher algorithm developed by Steve Babbage and Matthew Dodd. The cipher is designed to be used in hardware platforms with limited resources, and was one of the three ciphers accepted into Profile 2 of the eSTREAM portfolio. The algorithm is not patented and is free for any use.

The **ZPU** is a microprocessor stack machine designed by Norwegian company Zylin AS to run supervisory code in electronic systems that include a field-programmable gate array (FPGA).

**State encoding** assigns a unique pattern of ones and zeros to each defined state of a finite-state machine (FSM). Traditionally, design criteria for FSM synthesis were speed, area or both. Following Moore's law, with technology advancement, density and speed of integrated circuits have increased exponentially. With this, power dissipation per area has inevitably increased, which has forced designers for portable computing devices and high-speed processors to consider power dissipation as a critical parameter during design consideration.

- ↑ Harris, David and Harris, Sarah (2012-08-07).
*Digital design and computer architecture*(2nd ed.). San Francisco, Calif.: Morgan Kaufmann. p. 129. ISBN 978-0-12-394424-5. - ↑ "One-Hot Encoding".
*www.sciencedirect.com*. Retrieved 2020-01-20. - ↑ Xilinx. "HDL Synthesis for FPGAs Design Guide". section 3.13: "Encoding State Machines". Appendix A: "Accelerate FPGA Macros with One-Hot Approach". 1995.
- ↑ Cohen, Ben (2002).
*Real Chip Design and Verification Using Verilog and VHDL*. Palos Verdes Peninsula, CA, US: VhdlCohen Publishing. p. 48. ISBN 0-9705394-2-8.

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