►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
Thu Oct 30 2014, 06:02 PM
This is a chat box..create a thread if you need help...but we don't do homework
Tue Oct 28 2014, 07:33 PM
vinni
hi rickey...anyone got the pgm...pls gimme now
Tue Oct 28 2014, 06:35 PM
potla
hi vinni even i need that program. help me if you get it
Tue Oct 28 2014, 03:22 PM
vinni
1. Using a look-up table in Flash ROM and accumulator offset indexed addressing mode, write a program that acts as a timer. The timer should count from 0 to 59 seconds. After reaching 59, it should go back to 0 on the next second and continue to count up. The timer should use the seven-segment display. The look-up table should contain information on how to display the digits 0 – 9 on the seven-segment display
Tue Oct 28 2014, 03:22 PM
vinni
hello Rickey..i need this pgm very urgently
Tue Oct 28 2014, 01:42 AM
Boy Donald
Dear sir, thanks before. i have some project urgent for my school and my project need this digital countdown timer using 7 segmen display. but your project only show ten minutes countdown, i need your help, can you show me more to change the minute or set the time manually. thank you, sorry for disturbing you.
Tue Oct 28 2014, 01:32 AM
Boy Donald
dear sir
Tue Oct 28 2014, 01:19 AM
Boy Donald
Rickey you inspired me a lot but why i can not change the time ( minute
Sun Oct 26 2014, 02:51 AM
sandeep bankar
dear sir I m facing problem about..how to read number of incoming call in gsm 900 a. pls help how to read it in atmel avr microcontroller.
ajay_bhargav
Mon Oct 20 2014, 11:22 AM
@skrishna, please post in forum so we can help you better.

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Comments

prash5054
Thu Oct 30 2014, 06:34 AM
Max.otto
Mon Oct 27 2014, 01:23 PM
toypoy
Sun Oct 26 2014, 01:06 AM
hiswe
Thu Oct 23 2014, 04:18 PM
pddung93
Sun Oct 19 2014, 01:56 PM
msideal
Thu Oct 16 2014, 08:48 AM
robotgirl
Tue Oct 14 2014, 06:23 PM
BRV64
Mon Oct 13 2014, 05:48 AM

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Max.otto Avatar
Posted By Max.otto
Thu Oct 30 2014, 11:09 AM
Hello all, before generating i have to give PWM p...
prash5054 Avatar
Posted By prash5054
Thu Oct 30 2014, 06:40 AM
can u post the updated code for the above problem ...
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Posted By ExperimenterUK
Wed Oct 29 2014, 05:36 PM
Thank you for the feedback.It's good to hear when ...
msideal Avatar
Posted By msideal
Tue Oct 28 2014, 05:34 PM
ExperimenterUK: Thankyou so much for helping me......
msideal Avatar
Posted By msideal
Tue Oct 28 2014, 05:18 PM
thanks ExperimenterUK for your help.... I will try...
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Posted By ExperimenterUK
Mon Oct 27 2014, 10:29 PM
Your error seems to be the use of PINC, which is f...
msideal Avatar
Posted By msideal
Mon Oct 27 2014, 05:45 PM
i want to extend my i/o's by writing this code. i ...
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Posted By Max.otto
Mon Oct 27 2014, 01:30 PM
Hi all , i am working with PSoC 5LP. I have contin...
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Posted By gaurav7577
Mon Oct 27 2014, 09:53 AM
hello everyone i wanna interface blood pressure se...
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Posted By ExperimenterUK
Sun Oct 26 2014, 10:24 PM
sorry guys, i can't able to put the proteus filems...