RS-232/485 驱动器输出电压

Abstract

按照技术指标和电气接口介绍三种常见的串行数据标准：RS-232、RS-422和RS-485。介绍电缆端接技术、多个负载的使用、RS-232菊花链连接、RS-232至RS-485的转换、RS-485至RS-232的转换，以及RS-232端口供电的RS-485转换。

引言

“标准的奇妙之处在于有如此之多的选择。”这句话出现在最近一次关于光缆的会议中，但同样也适用于电气接口标准。随着不同行业内串行数据标准的独立发展，我们拥有的标准从未如此之多。

PC和电信应用领域最成功的串行数据标准可能就是RS-232。相类似，RS-485和RS-422也在工业应用领域最成功的标准之列。这些标准并不直接兼容。然而，对于控制和仪器仪表应用，往往必须在不同标准之间进行通信。本文讨论不同的标准(物理层指标)，介绍如何将一种标准转换为另一种标准，并演示如何在相同应用中组合不同的标准。

RS-232电气指标和典型连接

RS-232链路最初用于支持IBM PC上的调制解调器和打印机应用。然而，该标准现在支持各种外设与PC通信。RS-232标准定义为单端标准，用于以较低波特率(<20kbps)提高串行通信距离。多年以来，该标准几经变化，以支持较快的驱动器，例如MAX3225E，该器件能提供1Mbps数据传输速率。为了兼容RS-232，MAX3225E等收发器必须满足表1所列的电气指标。从典型连接(图1)可看出，利用硬件握手来控制数据流。

RS-232/485 驱动器输出电压

Abstract

Three common serial data standards are introduced in terms of technical specifications and electrical interfaces: RS-232, RS-422, and RS-485. Describes cable termination technology, the use of multiple loads, RS-232 Daisy chain connection, RS-232 to RS-485 conversion, RS-485 to RS-232 conversion, and RS-485 conversion for RS-232 port power supply.

introduction

"The wonderful thing about standards is that there are so many choices." This phrase came up at a recent conference on optical cables, but it also applies to electrical interface standards. With the independent development of serial data standards in different industries, we have never had so many standards.

Perhaps the most successful serial data standard for PC and telecommunications applications is RS-232. Similarly, RS-485 and RS-422 are among the most successful standards for industrial applications. These standards are not directly compatible. However, for control and instrumentation applications, it is often necessary to communicate between different standards. This article discusses different standards (physical layer metrics), shows how to convert one standard to another, and shows how to combine different standards in the same application.

RS-232 electrical specifications and typical connections

RS-232 links were originally used to support modem and printer applications on IBM PCS. However, the standard now supports a variety of peripherals to communicate with PCS. The RS-232 standard is defined as a single-ended standard for increasing serial communication distance at a lower baud rate (<20kbps). Over the years, the standard has changed several times to support faster drives, such as the MAX3225E, which offers 1Mbps data transfer rates. To be compatible with RS-232, transceivers such as the MAX3225E must meet the electrical specifications listed in Table 1. As you can see from a typical connection (Figure 1), a hardware handshake is used to control the flow of data.