 |
Business | Industries | Finance | Tax |
| Index: > A B C D E F G H I J K L M N O P Q R S T U V W X Y Z |
|
|||||
| First Prev [ 1 2 3 ] Next Last |
In electronics and computing, the flip-flop or bistable multivibrator is a pulsed digital circuit capable of serving as a one- bit memory. A flip-flop typically includes zero, one, or two input signals; a clock signal; and an output signal, though many commercial flip-flops additionally provide the complement of the output signal. Some flip-flops also include a clear input signal, which resets the current output. (In actuality, flip-flops are implemented as integrated circuit chips that also require power and ground connections.) Pulsing, or strobing, the clock causes the flip-flop to either change or retain its output signal, based upon the values of the input signals and the characteristic equation of the flip-flop. (Strobing the clock is a simplified view: any change of output state actually coincides with either the leading edge or the trailing edge of the clock pulse, and, to further complicate matters, may correspond to either a low-to-high or a high-to-low transition of the clock signal. The manufacturer's specification, or data sheet, annotates the precise semantics.)
Four types of flip-flops find common applicability in clocked sequential systems : these are called the T ("toggle") flip-flop, the S-R ("set-reset") flip-flop, the J-K flip-flop, and the D ("delay") flip-flop. The behavior of the flip-flop is described by what is termed the characteristic equation, which derives the "next" (i.e., after the next clock pulse) output, , in terms of the input signal(s) and/or the current output, .
The first electronic flip-flop was invented in 1919Events January January 1 Edsel Ford succeeds his father as head of the Ford Motor Company January 5 Spartacist uprising Socialist demonstrations in Berlin turn into attempted communist revolution with Spartacist League in the forefront January 9 Spartacus by W. H. Eccles and F. W. Jordan. It was initially called the Eccles-Jordan trigger circuit.
See also: monostableA monostable multivibrator is an electronic circuit that has two states, only one of which is stable. The circuit can be pushed into the unstable state by a control input. The time spent in the unstable state is usually controlled by the charging (or disc multivibrator, astableAn astable multivibrator is an electronic circuit that has two states, neither one which is stable. The circuit therefore behaves as an oscillator. The time spent in each state is usually controlled by the charging (or discharging) of a capacitor through multivibrator.
If the T input is high, the T flip-flop changes state ("toggles") whenever the clock input is strobed. If the T input is low, the flip-flop holds the previous value. This behavior is described by the characteristic equationAlgebra This article is about equations in mathematics. For equations in chemistry, see chemical equation. In mathematics, one often (not quite always) distinguishes between an identity which is an assertion that two expressions are equal regardless of th:
and the truth tableTruth tables are a type of mathematical table used in logic to determine whether an expression is true or whether an argument is valid. Truth tables derive from the work of Gottlob Frege, Charles Peirce and others from about the 1880s. They came to their:
| T | Q | Qnext |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
Left: A circuit symbol for a T-type flip-flop, where > is the clock input, T is the toggle input and Q is the stored data output.
The "set/reset" flip-flop sets (i.e., changes its output to logic 1, or retains it if it's already 1) if both the S ("set") input is 1 and the R ("reset") input is 0 when the clock is strobed. The flip-flop resets (i.e., changes its output to logic 0, or retains it if it's already 0) if both the R ("reset") input is 1 and the S ("set") input is 0 when the clock is strobed. If both S and R are 0 when the clock is strobed, the output does not change. If, however, both S and R are 1 when the clock is stobed, no particular behavior is guaranteed. This is often written in the form of a "truth table":
| S | R | Qnext |
| 0 | 0 | hold |
| 0 | 1 | 0 |
| 1 | 0 | 1 |
| 1 | 1 | unstable |
or more explicitly, showing the pre-clock value of Q as if it were another input:
| S | R | Q | Qnext |
| 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 1 |
| 0 | 1 | X | 0 |
| 1 | 0 | X | 1 |
| 1 | 1 | X | unstable |
X means "don't care", or the output will be the same regardless of which state the X is in.
Left: A circuit symbol for a SR-type flip-flop, where > is the clock input, S is the set input, R is the reset input, Q is the stored data output, and Q' is the inverse of Q.
It is the responsibility of the circuit designer to ensure that the S = R = 1 condition does not arise. Given this externally imposed condition, one typically avoids writing a characteristic equation for the S-R flip-flop. Various "master-slave" interconnections of S-R flip-flops are possible to achieve particular behaviors.
| Politics | Business | Finance |
 |
 |
 |
|