liquid-crystal displays (LCDs)


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INTRODUCTION

LED-based moving-message displays are becoming popular for transmitting information to large groups of people quickly. These can be used indoors or outdoors. We can find such displays in areas like railway platforms, banks, public offices, hotels, training institutes, nightclubs and shops.
Compared to LEDs, liquid-crystal displays (LCDs) are easy to interface with a microcontroller for displaying information as these have many built-in functions. But these can’t be observed from a distance and large size LCDs are very costly.
LED-based displays can be of two types: dot-matrix and segmental. If you implement a moving-message display with multiplexed dot-matrix LEDs, it will be very costly for displaying 16 characters or more at a time. Moreover, programming will require a lot of data memory or program memory space. An external RAM may be needed to complement a microcontroller like AT89C51.


Definition of A Microcontroller:
Microcontroller, as the name suggests, are small controllers. They are like single chip computers that are often embedded into other systems to function as processing/controlling unit. For example, the remote control you are using probably has microcontrollers inside that do decoding and other controlling functions. They are also used in automobiles, washing machines, microwave ovens, toys. etc, where automation is needed.
The key features of microcontrollers include:
High Integration of Functionality
Microcontrollers sometimes are called single-chip computers because they have on-chip memory and I/O circuitry and other circuitries that enable them to function as small standalone computers without other supporting circuitry.
Field Programmability, Flexibility
Microcontrollers often use EEPROM or EPROM as their storage device to allow field programmability so they are flexible to use. Once the program is tested to be correct then large quantities of microcontrollers can be programmed to be used in embedded systems.
Easy to Use


CHAPTER 5 SOFTWARE AND ITS WORKING

The source code ‘movmsg.asm’ is written in Assembly language and assembled using cross-compiler. It is well commented and easy to understand. Timer 1 has been used to generate a delay of around 1 ms for the switching gap between two consecutive displays. Thus , each display is enabled for 1 ms while displaying a message. The length of this cycle depends upon the length of the message string. The cycle repeats after a ‘0’ is encountered at the end of each message stored in the look-up table at the end of the program.