►Introduction

UART (Universal Asynchronous Receiver Transmitter) or USART (Universal Synchronous Asynchronous Receiver Transmitter) are one of the basic interface which you will find in almost all the controllers available in the market till date. This interface provide a cost effective simple and reliable communication between one controller to another controller or between a controller and PC.


►RS-232 Basics

RS-232 (Recommended Standard 232) is a standard for serial binary data signals connecting between a DTE (Data terminal equipment) and a DCE (Data Circuit-terminating Equipment).
Voltage Levels:
The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels. Valid signals are plus or minus 3 to 25 volts. The range near zero volts is not a valid RS-232 level; logic one is defined as a negative voltage, the signal condition is called marking, and has the functional significance of OFF. Logic zero is positive, the signal condition is spacing, and has the function ON.
So a Logic Zero represented as +3V to +25V and Logic One represented as -3V to -25V.

RS232 Voltage levels


►RS-232 Level Converters

Usually all the digial ICs works on TTL or CMOS voltage levels which cannot be used to communicate over RS-232 protocol. So a voltage or level converter is needed which can convert TTL to RS232 and RS232 to TTL voltage levels.
The most commonly used RS-232 level converter is MAX232. This IC includes charge pump which can generate RS232 voltage levels (-10V and +10V) from 5V power supply. It also includes two receiver and two transmitters and is capable of full-duplex UART/USART communication.

MAX232 Pin description
Fig A. - MAX232 Pin Description
MAX232 typical circuit
Fig B. - MAX232 Typical Connection Circuit



►MAX232 Interfacing with Microcontrollers

To communicate over UART or USART, we just need three basic signals which are namely, RXD (receive), TXD (transmit), GND (common ground). So to interface MAX232 with any microcontroller (AVR, ARM, 8051, PIC etc..) we just need the basic signals. A simple schematic diagram of connections between a microcontroller and MAX232 is shown below

MAX232 connections with microcontroller


In the next part of this tutorial we will discuss programming microcontroller to communicate over UART and software implementation of half duples UART.


◄ Introduction to Serial Communication  |  Microcontroller UART Programming ►

Conversation

ExperimenterUK
Sat Sep 13 2014, 12:34 PM
jaimin1212,Pimpalkhare Create a thread for your question
jaimin1212
Sat Sep 13 2014, 02:35 AM
i want to make self balancing robot using MPU6050 using atmega8.. please help to get data of gyro and accelerometer from this sensor through atmega8.
Thu Sep 11 2014, 09:00 AM
Sunil Pimpalkhare
Hello sir, I am trying to make Wearfin project https://www.youtube.com/watch?v=iZ6PVBvQf-g so can u help me in teaching how to built the program???
Thu Sep 11 2014, 02:21 AM
hariom panday
plz hlp me in my project
iec.naga
Tue Sep 09 2014, 01:19 AM
spi
Mon Sep 08 2014, 08:14 AM
fameem
water changing in fish tank automatically using microcontoller with timer. send idea to me
dexter_a
Sat Sep 06 2014, 11:09 AM
hello guys
Sat Sep 06 2014, 10:10 AM
munaxa
plx guide me
Sat Sep 06 2014, 10:09 AM
munaxa
hi i want to buy plx guie me
ajay_bhargav
Sat Sep 06 2014, 03:10 AM
@Ben, Its hard to undrstand the context like this. If you can post in forum with some example code we might answer you better.

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deepbhadani
Fri Sep 19 2014, 01:08 PM
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Tue Sep 16 2014, 10:53 AM
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Fri Sep 12 2014, 12:45 PM
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Tue Sep 09 2014, 01:09 AM

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