Notes_20141031-Flip-Flop+Setup time things

最新推荐文章于 2021-07-20 16:53:54 发布

转载最新推荐文章于 2021-07-20 16:53:54 发布 · 706 阅读

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#Flip Flop #Setup time #Digital logic #Computer memory

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本文探讨了电子学中Flip-Flop与Latch的基本概念及历史背景。解释了这两种电路如何储存状态信息，并介绍了它们的不同类型及其命名由来。

Flip-Flop,

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Here I am very interested in the name of Flip-flop and Latch.

By wiki, I know.

In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. Flip-flops can be either simple (transparent or opaque) or clocked (synchronous or edge-triggered). Although the term flip-flop has historically referred generically to both simple and clocked circuits, in modern usage it is common to reserve the term flip-flop exclusively for discussing clocked circuits; the simple ones are commonly called latches.

Here is the basic knowledge, we all known. But did you know why we name it as Flip-flop?

The first electronic flip-flop was invented in 1918 by William Eccles and F. W. Jordan.It was initially called the Eccles–Jordan trigger circuit and consisted of two active elements (vacuum tubes). Such circuits and their transistorized versions were common in computers even after the introduction of integrated circuits, though flip-flops made from logic gates are also common now.Early flip-flops were known variously as trigger circuits or multivibrators.

According to P. L. Lindley, a JPL engineer, the flip-flop types discussed below (RS, D, T, JK) were first discussed in a 1954 UCLA course on computer design by Montgomery Phister, and then appeared in his book Logical Design of Digital Computers. Lindley was at the time working at Hughes Aircraft under Eldred Nelson, who had coined the term JK for a flip-flop which changed states when both inputs were on (a logical "one"). The other names were coined by Phister. They differ slightly from some of the definitions given below. Lindley explains that he heard the story of the JK flip-flop from Eldred Nelson, who is responsible for coining the term while working at Hughes Aircraft. Flip-flops in use at Hughes at the time were all of the type that came to be known as J-K. In designing a logical system, Nelson assigned letters to flip-flop inputs as follows: #1: A & B, #2: C & D, #3: E & F, #4: G & H, #5: J & K. Nelson used the notations "j-input" and "k-input" in a patent application filed in 1953.

"...Sometimes the terms flip-flop and latch are used interchangeably..."

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Setup time + Hold time + Recovery time + Removal time

The metastability in flip-flops can be avoided by ensuring that the data and control inputs are held valid and constant for specified periods before and after the clock pulse, called the setup time (t_su) and the hold time (t_h) respectively. These times are specified in the data sheet for the device, and are typically between a few nanoseconds and a few hundred picoseconds for modern devices. Depending upon the flip-flop's internal organization, it is possible to build a device with a zero (or even negative) setup or hold time requirement but not both simultaneously.