Digital-electronics 简明教程
Programmable Logic Array (PLA)
在本章中，我们将讨论 Programmable Logic Array (PLA) 、其框图和应用。可编程逻辑阵列（PLA）是一种可编程逻辑器件（PLD）。从历史上讲，PLA 是第一个 PLD 器件。它包含一个与或门阵列/矩阵，其配置根据应用需要进行。
In this chapter, we will talk about Programmable Logic Array (PLA), its block diagram, and applications. The programmable logic array (PLA) is a type of programmable logic device (PLD). Historically, PLA is the first PLD device. It contains an array/matrix of AND and OR gates whose configuration is done as per the needs of applications.
在 PLA 中，使用一组熔断链路建立或取消在与操作中文字的触点或在或操作中乘积项的触点。因此，PLA 是一种 PLD，允许对与矩阵和或矩阵进行编程。
In a PLA, a set of fusible links is used to establish or remove the contact of a literal in the AND operation or contact of a product term in the OR operation. Therefore, a PLA is a type of PLD that allows both AND matrix and OR matrix to program.
在数字电子学中，PLA 用于设计和实现各种复杂的组合电路。但是，一些 PLA 也有存储器元件，因此它们也可以用于实现顺序电路。
In digital electronics, PLAs are used to design and implement a variety of complex combinational circuits. However, some PLAs also have a memory element, hence they can be used to implement sequential circuits as well.
Block Diagram of PLA
可编程逻辑阵列（PLA）是一种固定架构可编程逻辑器件（PLD），它由可编程与门和或门组成。PLA 包含一个可编程与阵列，其后跟一个可编程或阵列。
A programmable logic array (PLA) is a type of fixed architecture programmable logic device (PLD) which consists of programmable AND and OR gates. A PLA contains a programmable AND array which is followed by a programmable OR array.
block diagram of the PLA 如以下图形所示−
The block diagram of the PLA is shown in the following figure −
它包含以下 components −
It consists of the following main components −
Input Buffer
在 PLA 中使用输入缓冲器来避免驱动输入的源上的负载效应。
The input buffer is used in PLA to avoid the loading effect on the source that drives the inputs.
AND Array/Matrix
在 PLA 中使用与阵列/矩阵来生成乘积项。
The AND array/matrix is used in PLA to generate the product terms.
OR Array/Matrix
在 PLA 中，或阵列/矩阵用于生成所需的输出。这是通过对乘积项进行或运算来生成和项来完成的。
In a PLA, the OR array/matrix is used to generate the desired output. This is done by Oring the product terms to produce the sum terms.
Combinational Logic Design using PLA
在数字电子领域，PLA 被广泛用于设计组合逻辑电路。使用 PLA 设计组合电路的最大优势在于，PLA 由可编程与阵列和或阵列组成，可以实现定制所需的逻辑功能。
In the field of digital electronics, the PLAs are extensively used for designing combinational logic circuits. The greatest advantage of designing combinational circuits using PLAs is that PLA consist of programmable AND and OR arrays which allows to implement custom desired logic functions.
下文解释了使用 PLA 的 step-by-step procedure to design a combinational logic circuit −
The step-by-step procedure to design a combinational logic circuit using PLAs is explained below −
Step 1 ——编制 PLA 程序表，其中显示输入、乘积项和输出。
Step 1 − Develop a PLA program table that shows the inputs, product terms, and outputs.
Step 2 ——设计可生成所需乘积项的与矩阵。
Step 2 − Design the AND matrix that can generate the desired product terms.
Step 3 ——设计可生成所需输出的或矩阵。
Step 3 − Design the OR matrix that can generate the desired output.
Step 4 ——设计求反/不求反矩阵，以设置低电平有效或高电平有效输出。
Step 4 − Design the invert/non-invert matrix to set the active-low or active-high output.
Step 5 ——最后，通过利用 PLA 程序表对 PLA 编程。
Step 5 − Finally, program the PLA by utilizing the PLA program table.
让我们借助一个示例了解使用 PLA 进行组合电路设计的这个过程。
Let us understand this process of combinational circuit design using PLA with the help of an example.
Example
使用可编程逻辑阵列 (PLA) 设计全加器电路。
Design a full-adder circuit using programmable logic array (PLA).
全加器由三个输入和两个输出组成。由于它有 3 个输入，因此共有 8 个乘积项，这些乘积项在全加器的以下真值表中给出 -
A full-adder consists of three-inputs and two outputs. Since it has 3 inputs, thus there are total 8 product terms which are given in the following truth table of the full adder −
Inputs |
Outputs |
A |
B |
Cin |
S |
Cout |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
0 |
0 |
1 |
0 |
1 |
0 |
0 |
1 |
1 |
0 |
1 |
1 |
0 |
0 |
1 |
0 |
1 |
0 |
1 |
0 |
1 |
1 |
1 |
0 |
0 |
1 |
1 |
1 |
1 |
1 |
从这个真值表中，输出和（S）和输出进位（Cout）由下式给出：
From this truth table, the output sum (S) and the output carry (Cout) are given by,
\mathrm{S \: = \: \sum \: m(1,2,4,7)}
\mathrm{C_{out} \: = \: \sum \: m(3,5,6,7)}
因此，它们的布尔表达式将为：
Thus, their Boolean expressions will be,
\mathrm{S \: = \: \overline{A} \: B \: \overline{C_{in}} \: + \: \overline{A} \: \overline{B} \: C_{in} \: + \: A \: \overline{B} \: \overline{C_{in}} \: + \: A \: B \: C_{in}}
\mathrm{C_{out} \: = \: A \: B \: + \: B \: C_{in} \: + \: A \: C_{in}}
从这两个布尔表达式中，我们可以看出有七个乘积项和两个求和项。对此全加器电路的 PLA 程序表如下图所示 -
From these two Boolean expressions, we can see that there are seven product terms and two sum terms. The PLA program table for this full-adder circuit is shown below −
Sr.No |
Product Terms |
Inputs |
Outputs |
A |
B |
Cin |
S |
Cout |
1 |
$\mathrm{\overline{A} \: B \: \overline{C_{in}}}$ |
0 |
1 |
0 |
1 |
- |
2 |
$\mathrm{\overline{A} \: \overline{B} \: C_{in}}$ |
0 |
0 |
1 |
1 |
- |
3 |
$\mathrm{A \: \overline{B} \: \overline{C_{in}}}$ |
1 |
0 |
0 |
1 |
- |
4 |
$\mathrm{A \: B \: C_{in}}$ |
1 |
1 |
1 |
1 |
- |
5 |
$\mathrm{A \: B }$ |
1 |
1 |
- |
- |
1 |
6 |
$\mathrm{B \: C_{in}}$ |
- |
1 |
1 |
- |
1 |
7 |
$\mathrm{A \: C_{in}}$ |
1 |
- |
1 |
- |
1 |
T |
在这个 PLA 程序表中，“1”代表连接，“-”代表输出中没有该积项。“T”代表真，表示有效的正输出。
In this PLA program table, "1" stands for the connection and "-" stands for the absence of the product term in the output. "T" stands for true and it represents the active-high output.
全加器的 PLA 电路图为下图所示。
The PLA circuit diagram of the full-adder is shown in the following figure.
这个例子说明使用 PLA 实现组合逻辑电路的完整分步过程。
This example illustrates the complete step-by-step procedure to implement a combinational logic circuit using PLA.
Advantages of PLAs
以下是可编程逻辑阵列 (PLA) 的一些关键优势，使它们在数字电子领域不可或缺−
The following are some key advantages of Programmable Logic Arrays (PLAs) that make them indispensable in the field of digital electronics −
-
PLAs provide flexibility in terms of design and implementation of a variety of digital logic operations. PLAs can be used to implement custom logic functions required to fulfil the needs of different applications.
-
PLAs also minimize the time required to design and develop a new digital circuit or system.
-
PLAs provide a less expensive way of implementing highly complex digital logic functions. PLAs eliminate the need of discrete components to implement a logic function, hence they result in space efficiency.
-
Since PLAs are programmable, they can be modified on their designs without re-fabricating the entire circuit.
Disadvantages of PLAs
但是，如上所述，PLA 提供了诸多优势。但它们也有一些缺点，如下所列−
However, PLAs offer several advantages as discussed above. But they also have some disadvantages which are listed below −
-
For a large number of inputs and outputs, PLAs are highly complex to design and implement. Being a fixed architecture device, PLAs have limited performance in terms of speed and processing power.
-
A PLA is generally optimized for a specific application, as it has a fixed number of AND gates and OR gates. This constraint disallows the designers to implement highly complex logic functions with the same PLA.
-
Program a PLA is a time consuming and complex process.
Applications of PLAs
可编程逻辑阵列 (PLA) 广泛应用于不同领域的各种应用。以下是 PLA 的一些常见应用−
Programmable Logic Arrays (PLAs) are widely used in various applications across different fields. The following are some common applications of PLAs −
-
PLAs are used in the field of digital signal processing to implement various logical functions, such as filtering, convolution, Fourier transformation, etc.
-
In control systems, PLAs are used to implement control logic functions of various components like feedback, PID controllers, state machines, etc.
-
PLAs are used to perform different types of arithmetic operations like addition, subtraction, multiplication, and division.
-
PLAs also find their application in the field data compression and encryption technologies. PLAs are used in digital communication systems and networking equipment to implement algorithms for protocol handling, packet processing, error detection and correction, and more.
-
PLAs are also used in different measuring instruments such as digital oscilloscopes, protocol analyzers, logic analyzer, etc.
Conclusion
PLA 不过是一种数字逻辑器件，用于在不需要与门、或门等分立器件的情况下实现复杂的数字功能。在本章中，我们解释了可编程逻辑阵列 (PLA) 的基础知识和应用。
A PLA is nothing but a kind of digital logic device used to implement complex digital functions without need of discrete components like AND gates, OR gates, etc. In this chapter, we explained the basics and applications of programmable logic arrays (PLAs).