►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

Fri Dec 19 2014, 11:31 AM
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ajay_bhargav
Fri Dec 12 2014, 04:38 AM
@Abdul BAsit, Post in forum please. We will help you.
Wed Dec 10 2014, 06:41 PM
Abdul BAsit
I am working on smoke detector using AT89S52 and dont know how its wors..kindly send me circuit diagram and code for its hardware & software implementation
Tue Dec 09 2014, 11:30 AM
Irinel
Please send me the content of that cd-rom (embedded c - michael j pont. Thank you.
Tue Dec 09 2014, 02:45 AM
kmyo
please give me the operation of 12v trickle charger
Sun Dec 07 2014, 07:50 AM
hidawi
we need the circuit diagrom of the remote control of iduction motor by android appliction
PsySc0rpi0n
Tue Dec 02 2014, 10:30 AM
I have no idea... I'm new to micro controllers
Tue Dec 02 2014, 08:35 AM
samarnath dev
how can usb key bord interfasing to dot matrx led moving, by asm51 ?
Tue Dec 02 2014, 08:32 AM
samarnath dev
how can usb key bord interfasing to 8051 by asm code?

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naimish324
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sankalp_s Avatar
Posted By sankalp_s
Sat Dec 20 2014, 05:31 PM
For what you want,it is easier to not use interrup...
ExperimenterUK Avatar
Posted By ExperimenterUK
Fri Dec 19 2014, 09:58 PM
For what you want,it is easier to not use interrup...
sankalp_s Avatar
Posted By sankalp_s
Fri Dec 19 2014, 06:04 PM
This version works.Edit it to use either method. ...
muhibraza Avatar
Posted By muhibraza
Fri Dec 19 2014, 08:05 AM
software_developer Avatar
Posted By software_developer
Fri Dec 19 2014, 04:54 AM
Which files i have to use?Please give me .zip fold...
ExperimenterUK Avatar
Posted By ExperimenterUK
Fri Dec 19 2014, 12:21 AM
This version works.Edit it to use either method. ...
sankalp_s Avatar
Posted By sankalp_s
Thu Dec 18 2014, 08:40 PM
SIR THIS CODE IS NOT WORKING.. ORG 000H ; starting...
sankalp_s Avatar
Posted By sankalp_s
Thu Dec 18 2014, 08:36 PM
i've tried this code but faced a syntax error on l...
sankalp_s Avatar
Posted By sankalp_s
Thu Dec 18 2014, 08:32 PM
SIR THIS CODE IS NOT WORKING.. ORG 000H ; starting...
ajay_bhargav Avatar
Posted By ajay_bhargav
Thu Dec 18 2014, 04:24 AM
Code is all ok.. just change EXT0 to EX0... By mis...