One hot
Encyclopedia
In digital circuits, one-hot refers to 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). For example, the output of a decoder
is usually a one-hot code, and sometimes the state of a state machine is represented by a one-hot code. A similar implementation in which all bits are '1' except one '0' is sometimes called one-cold.
For example, a ring counter
that has fifteen sequentially-ordered states would have a 'one-hot' implementation of fifteen 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 fifteenth flip flop. The first flip flop in the chain represents the first state, the second represents the second state, and so on to the fifteenth 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 fifteenth state after which the state machine returns to the first state.
Decoder
A decoder is a device which does the reverse operation of an encoder, undoing the encoding so that the original information can be retrieved. The same method used to encode is usually just reversed in order to decode...
is usually a one-hot code, and sometimes the state of a state machine is represented by a one-hot code. A similar implementation in which all bits are '1' except one '0' is sometimes called one-cold.
For example, a ring counter
Ring counter
A ring counter is a type of counter composed of a circular shift register. The output of the last shift register is fed to the input of the first register.There are two types of ring counters:...
that has fifteen sequentially-ordered states would have a 'one-hot' implementation of fifteen 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 fifteenth flip flop. The first flip flop in the chain represents the first state, the second represents the second state, and so on to the fifteenth 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 fifteenth state after which the state machine returns to the first state.
External links
- Encoding State Machines at xilinx.com
See also
- Unary numeral systemUnary numeral systemThe unary numeral system is the bijective base-1 numeral system. It is the simplest numeral system to represent natural numbers: in order to represent a number N, an arbitrarily chosen symbol representing 1 is repeated N times. For example, using the symbol | , the number 6 is represented as ||||||...
- Uniqueness quantificationUniqueness quantificationIn mathematics and logic, the phrase "there is one and only one" is used to indicate that exactly one object with a certain property exists. In mathematical logic, this sort of quantification is known as uniqueness quantification or unique existential quantification.Uniqueness quantification is...
- XOR gateXOR gateThe XOR gate is a digital logic gate that implements an exclusive or; that is, a true output results if one, and only one, of the inputs to the gate is true . If both inputs are false or both are true , a false output results. Its behavior is summarized in the truth table shown on the right...