A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications. Microcontrollers are used in automatically controlled products and devices, such as automobile engine control systems, implantable medical devices, remote controls, office machines, appliances, power tools, and toys. By reducing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally control even more devices and processes. Mixed signal microcontrollers are common, integrating analog components needed to control non-digital electronic systems. Some microcontrollers may use Four-bit words and operate at clock rate frequencies as low as 4 kHz, for low power consumption (milliwatts or microwatts). They will generally have the ability to retain functionality while waiting for an event such as a button press or other interrupt; power consumption while sleeping (CPU clock and most peripherals off) may be just nanowatts, making many of them well suited for long lasting battery applications. Other microcontrollers may serve performance-critical roles, where they may need to act more like a digital signal processor (DSP).

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3. HARDWARE DESCRIPTION

• Raisonance is one of the embedded system vendors that provide the development tools for the 8051 microcontroller. The software compiles the firmware code and generates an ’Intel Hex’ file. Flash Magic is a free Windows application software that allows easy programming of Philips Flash Microcontrollers. The software loads the ’Intel Hex’ file to the microcontroller by using its in-system programming mode communicating through serial port.

#include #include typedef unsigned char uchar; typedef unsigned long ulong; typedef unsigned int uint; #define TIMER_RELOAD (-921) #define port_delay() _nop_(), _nop_(), _nop_(), _nop_() uint count; ulong value; uchar state,rdata; void timer0(void) interrupt 1 using 1 { count++; TH0 = (uchar)(TIMER_RELOAD>>8); TL0 = (uchar)TIMER_RELOAD; } /* void delay(uint n) { n = count + n; while (n != count); } */ void io_open(void) {

IE = 0x92; //1001 0010 SCON = 0x50; //0101 0000

REN = 1;

TL0 = (uchar)TIMER_RELOAD; TH0 = (uchar)TIMER_RELOAD >> 8; TH1 = TL1 = 0xFA;

TR0 = 1; TR1 = 1;

} void main(void) { io_open(); while(1) {

P0 = P2; }}

This integration drastically reduces the number of chips and the amount of wiring and circuit board space that would be needed to produce equivalent systems using separate chips. Furthermore, on low pin count devices in particular, each pin may interface to several internal peripherals, with the pin function selected by software. This allows a part to be used in a wider variety of applications than if pins had dedicated functions. Micro-controllers have proved to be highly popular in embedded systems since their introduction in the 1970s. Some microcontrollers use a Harvard architecture: separate memory buses for instructions and data, allowing accesses to take place concurrently. Where a Harvard architecture is used, instruction words for the processor may be a different bit size than the length of internal memory and registers; for example: 12-bit instructions used with 8-bit data registers. The decision of which peripheral to integrate is often difficult. The microcontroller vendors often trade operating frequencies and system design flexibility Manufacturers have to balance the need to minimize the chip size against additional functionality. Microcontroller architectures vary widely. Some designs include general-purpose microprocessor cores, with one or more ROM, RAM, or I/O functions integrated onto the package. Other designs are purpose built for control applications. A micro-controller instruction set usually has many instructions intended for bit-wise operations to make control programs more compact. For example, a general purpose processor might require several instructions to test a bit in a register and branch if the bit is set, where a micro-controller could have a single instruction to provide that commonly-required function.