分立元件-TTL转RS232适配器详解(内容非常详细)

TTL to RS232 adaptor Explained

TTL

转

RS232

适配器详解

How to build a simple TTL to RS232 adaptor for your

microcontroller projects. You should be able to

scrounge

all

the parts you need or buy them at your local Radio Shack. In

this article I explain how the adaptor works and provide many

links to more information you need to know as a

microcontroller hobbyist. This article should be very helpful to

those that receive the

free Arduino compatible kit offered by

uC hobby

as part of the Arduino Microcontroller kit giveaway.

作为一个业余的微控 制器爱好者，在这片文章里，我会解释这

个适配器是如何工作的，并且提供很多链接让大 家来了解所需

要的信息。

Just about every microcontroller available today includes at lest one UART or serial port. Serial ports are

the most common way to communicate with auC or other devices such as GPS receivers. The most

common interface type is RS232, only a simple conversion from the logic level signals of the uC serial RX

and TX pins is required to work with RS232.

RS232 101

For a detailed understanding of RS232 and serial interfacing in general, go to

Beyond Logic

, the mother

load for interfacing information. From this point forward I will assume you know enough about serial

communications and will focus on the why and how for the TTL to RS232 adaptor.

< br>通过前面这点知识，我将假定知道了关于串口通信足够的知识，然后把注意力集中在

TTL-to- RS232

适配

器上。

The easiest way to make an RS232 interface is with an interface IC, the

MAX232

for example. There are

a great number of different dedicated chips available with cost ranging in the $$1-$$3 range. You simply

add a few capacitors and you have a reliable RS232 interface. For hobby work you can buy

a versatile

RS232 adaptor from SparkFun

for about $$7 as a kit. The picture shows the kit parts and the assembled

adaptor. I highly recommend this kit if you want to solve this problem quickly and at little cost.

The basic problem we have to solve is that theuC UART is a logic level device and RS232 is not. To send

data over RS232 the voltages need to be about +/-10V while the output at the uC will be 0-5V or 0-3.3V.

To see a zero signal the receiving RS232 device needs to see a negative voltage. We also need to invert

the phase of our logic signal so that a 1 (5V) is converted to the negative voltage (-10).

Typically the threshold for 1 vs. 0 in the RS232 receiver is slightly above 0V we can get away with using

less then +/- 10V. +/-5V should be sufficient for almost any devices. We usually have +5V available in our

electronics projects but the negative voltage is a problem.

在

RS232

接收器里，典型的

1

到

0

的阈值电压是稍微大于

0V

即可，从而我们可以侥幸使用小于

+/- 10V

的电压做成。 对于大多数的器件，

+/-5V

应该足够。在我们的电子工程中 ，经常可以得到

+5V

的电压，但

是想 要得到负电压确实一个难题。

After doing a quick search on the net I found that many TTL to RS232 adaptors use

a common two

transistor circuit

. I have recreated the schematic for this circuit and will explain briefly how it works below.

This is the circuit used in

the recommended SparkFun kit

.

This is basically the same

schematic provided by SparkFun

with some re-arranging to make it easier to

explain. Each major section is enclosed in a dotted line with a name for that region. Each of these regions

is explained below.

这个电路和

SparkFun

提供的原理图基本上是一样了，只是重新调整了一下 使我们更容易了解。每个主要

部分都使用虚线框起来了，并且给每个部分都命名了。每个 部分在下面都有解释。

PC RS232

This shows the DB9 connector which would connect to your PC. The PC has a male connector so you

would need a female if you built this circuit with an integrated cable. I recommend a DB9 female

connector so that a straight through serial cable could be used. While there are many other signals

available on the serial port we are only concerned with Ground, RX, and TX. Ground is the signal

reference against which all other signals are measured. RX is the serial data input to the PC. The voltage

levels here should be switching between +/-10V. We will get away with -10 and +5 for this circuit.

这部分是连接到

PC

的

DB9

连接座，

PC

一般有一个公头连接器，所以如果你的电路使用集成线缆的话你

则需要一个母 头。我建议使用母头，如此就能够使用线缆直接连接了。由于在这个端口有很多的可用信号

线，我们只需要使用

Ground

、

RX

和

TX

即可。

Ground

是其他可测量信号的参考信号

RX