Digital-electronics 简明教程

Programmable Array Logic (PAL)

在上一章中，我们解释了 Programmable Logic Array (PLA) ，它是一种可编程逻辑器件 (PLD)。本章将讨论另一种称为 Programmable Array Logic (PAL)的可编程逻辑器件。

In the previous chapter, we explained Programmable Logic Array (PLA) which is a first programmable logic device (PLD). This chapter will deal with another type of programmable logic device called Programmable Array Logic (PAL).

PLA 和 PAL 之间的主要区别在于，在 PLA 器件中，AND 阵列和 OR 阵列都是可编程的，而在 PAL 的情况下，OR 阵列是固定的，而 AND 阵列是可编程的。可编程阵列逻辑 (PAL) 也由 AND 门和 OR 门阵列组成。

The primary difference between PLA and PAL is that in a PLA device, both AND array and OR array are programmable, whereas in the case of PAL, the OR array is fixed while the AND array is programmable. A programmable array logic (PAL) also consists of arrays of AND and OR gates.

PAL 具有的最重要的优势在于它很容易编程，因为它只包含一个可编程 AND 门阵列，尽管它不像 PLA 那样灵活。

The most significant advantage that the PAL has is that it is very easy to program, as it contains only a programmable AND gate array, although it is not as flexible as the PLA.

What is a PAL?

在数字电子领域，有几种不同类型可编程逻辑器件或 PLD。可编程阵列逻辑 (PAL) 也是一种用于设计和实现各种自定义逻辑功能的 PLD。这些可编程阵列逻辑器件使数字设计师能够以高度的灵活性和效率开发复杂的逻辑结构。

In the field of digital electronics, there are several different types of programmable logic devices or PLDs. The Programmable Array Logic (PAL) is also a type of PLD used to design and implement a variety of custom logic functions. These programmable array logic devices allow digital designers to develop complex logic structures with high flexibility and efficiency.

从结构上来说，一个 PAL 器件包含一个可编程 AND 门阵列，连接至一个固定的 OR 门阵列。通过互连输入线路、AND 门，和 OR 门，这个阵列结构有助于实现各种逻辑函数。

Construction-wise, a PAL device consists of an array of programmable AND gates connected to a fixed array of OR gates. This array structure helps to implement various logic functions by interconnecting the input lines, AND gates and OR gates.

Block Diagram of PAL

与 PLA 类似，可编程阵列逻辑 (PAL) 也是一种固定架构逻辑器件，具有一个可编程 AND 门阵列和一个固定 OR 门阵列，如下图所示-

Similar to PLA, the Programmable Array Logic (PAL) is also a type of fixed architecture logic device having an array of programmable AND gates and an array of fixed OR gates as shown in the following figure −

block diagram of pal

从这个框图可以看出，PAL 由以下三个主要组件组成-

From this block diagram, it can be seen that a PAL consists of the following three main components −

  1. Input Buffers

  2. AND Gate Array

  3. OR Gate Array

这些组件通过一个用“X”表示的编程连接连接在一起。在实践中，这些编程连接可以通过 EPROM 单元或其他编程技术来实现。

These components are connected together through a programmed connection indicated by "X". In practice, these programmed connections can be made through EPROM cells or other programming technologies.

Combinational Logic Design Using PAL Devices

我们可以使用可编程阵列逻辑 (PAL) 器件设计组合逻辑电路。在使用 PAL 设计组合逻辑时，重要的是要注意，求和积形式的布尔表达必须简化才能适合 PAL 的每一段。

We can design combinational logic circuits using Programmable Array Logic (PAL) devices. While designing combinational logic using PAL, it is important to note that the Boolean expression in the sum products form must be simplified to fit into each section of the PAL.

由于 OR 门阵列是固定的，因此馈入每个 OR 门的乘积项数量不能更改。如果出现乘积项数量过多，那么必须为该段实现布尔函数。

Because the array of OR gates is fixed, the number of product terms fed to each OR gate cannot be changed. If there is a situation when the number of product terms are more, then the Boolean function must be implemented for that section.

让我们借助示例来了解使用 PAL 器件的组合逻辑设计。

Let us understand the combinational logic design using PAL devices with the help of examples.

Example

考虑一个具有 3 个输入和 2 个输出的组合逻辑电路。输出的逻辑函数如下所示。使用 PAL 实现此电路。

Consider a combinational logic circuit which has 3 inputs and 2 outputs. The logic functions for the outputs are given below. Implement this circuit using PAL.

\mathrm{X(A,B,C) \: = \: \sum \: m(1,2,4,6)}

\mathrm{Y(A,B,C) \: = \: \sum \: m(0,1,3,6,7)}

获取给定逻辑函数的布尔表达式，

Obtaining the Boolean expressions for the given logic functions,

combinational logic design using pal devices

从这些卡诺图中，我们得到，

From these K-maps, we get,

\mathrm{X \: = \: A\overline{C} \: + \: B\overline{C} \: + \: \overline{A} \: \overline{B} C}

\mathrm{Y \: = \: \overline{A} \:\overline{B} \: + \: BC \: + \: AB}

现在，准备这些输出函数的 PAL 程序表，如下所示-

Now, prepare the PAL program table for these output functions, which is given below −

Product Terms

AND Gate Inputs

A

B

C

1

$\mathrm{A \: \overline{B}}$

1

-

0

2

$\mathrm{B \: \overline{C}}$

-

1

0

3

$\mathrm{\overline{A} \: \overline{B} \: C}$

0

0

1

4

$\mathrm{\overline{A} \: \overline{B}}$

0

0

-

5

$\mathrm{B \: C}$

-

1

1

6

$\mathrm{A \: B}$

1

1

现在，让我们按照这个表实现 PAL 逻辑电路。该电路图如下图所示-

Now, let’s implement the PAL logic circuit as per this table. This circuit diagram is shown in the following figure −

pal logic circuit diagram

这就是我们可以使用可编程阵列逻辑 (PAL) 实现逻辑函数的方法。

This is how we can implement a logic function using Programmable Array Logic (PAL).

Advantages of PAL

在数字电子领域，可编程阵列逻辑 (PAL) 由于其提供的诸多优势而广泛用于组合和时序电路设计。

In the field of digital electronics, Programmable Array Logic (PAL) is widely used in combinational and sequential circuit designing due to the several advantages it offers.

  1. PAL devices provide greater flexibility in design and implementation of custom logic functions, as it can be programmed by making interconnections between the input lines and the AND gates so that it can meet the requirements of a specific application.

  2. PAL devices also provide less expensive ways of implementing complex logic functions. This is because PALs eliminate the requirement of custom fabrication processes due to its ability to program.

  3. PALs also help to minimize the time required for developing and launching the electronic products.

  4. Due to their high integration density, PALs allow for implementing multiple logic functions within a single device. Consequently, they help in developing compact and efficient designs.

Disadvantages of PAL

然而，可编程阵列逻辑（PAL）具有如上所述的几个优点，但它们也有一些缺点，如下所列：

However, Programmable Array Logics (PALs) have several advantages as given above, but they also have some disadvantages as listed below −

  1. PAL devices have some limitations in terms of complexity in the implementation of logic functions. This is because, a PAL contains a certain number of input lines, AND gates, and OR gates. Thus, if we need to implement a complex logic function, then we can require multiple PALs.

  2. PAL devices have a fixed architecture which contains an array of fixed OR gates and an array of programmable AND gates. Therefore, these devices cannot be used to implement certain logic functions.

  3. Since PALs have a finite number of input and output lines. This results in a limit in terms of the I/O connectivity of the electronic device.

  4. It is very complex and time-consuming process to program a PAL device. It also requires some specialized tools and expertise.

Applications of PAL

可编程阵列逻辑（PAL）广泛应用于数字电子领域的各种应用中。PAL的一些常见应用如下：

Programmable Array Logics (PALs) are extensively used in a variety of applications in the field of digital electronics. Some common applications of PALs are listed below −

  1. PALs are used in embedded systems for implementing control logics, providing interfacing between different components, sensors, and other subsystems, and performing various signal processing tasks like filtering, modulation, demodulation, signal conditioning, etc.

  2. In communication systems, PALs are employed for implementing encoding and decoding algorithms, protocol processing, error detection and correction, multiplexing and demultiplexing, etc.

  3. PALs are also used in the field of automotive electronics for implementing control logics for managing engine functions, fuel injection, emission control system, anti-lock braking system, audio system, navigation, and driver assistance system.

  4. In industrial automation and robotics, the PALs play an important role, as they help to develop logic functions for controlling and monitoring industrial processes, sensors, and other components.

  5. PALs are also used in consumer electronics like washing machines, microwave ovens, home automation systems, etc. to implement their control functions.

Conclusion

PAL是一种可编程逻辑器件，用于实现组合逻辑与顺序逻辑，并广泛用作各种领域的通用设备。

A PAL is a type of programmable logic device used to implement combinational and sequential logics and is used as a versatile device across a wide range of fields.

由于其灵活性更高、易于编程和可靠性，PAL已成为数字电子领域的重要工具。

Due to its greater flexibility, easy programmability, and reliability, PAL has become an important tool in the field of digital electronics.