The embedded system components include its hardware and the software.

Hardware components of the embedded system are : The most important units in the embedded system is the processor. The various units in the embedded system includes the following :

1. Microprocessor or Microcontroller
2. Timers / Counters
3. Serial and parallel communication ports
4. Interrupt controller
5. Input devices with the driver circuit
6. Output devices with the driver circuits
7. Power supply, Reset and Oscillator circuits
8. Any application specific circuits.

Processor : A microprocessor is a computer processor which incorporates the functions of a computer's central processing unit (CPU) on a single integrated circuit (IC), or at most a few integrated circuits. The microprocessor is a multipurpose, clock driven, register based, digital-integrated circuit which accepts binary data as input, processes it according to instructions stored in its memory, and provides results as output.

Microprocessors contain both combinational logic and sequential digital logic. Microprocessors operate on numbers and symbols represented in the binary numeral system.

Peripheral and Memory components of an Embedded System

1. Timer / Counter : In Microprocessor System, Timer is used to provide a delay and counter which is used to count incoming pulses. In large systems, where microprocessor's wastage time is critical, a separate timer IC like IC8254 can be used. These counters can work as counter or can provide accurate time delays. Microcontrollers have these timers on-chip.

2. Interrupt Controller : The various peripheral controllers on-chip in case of a microcontroller need to be properly prioritized and controlled properly. The microprocessors require external interrupt controller, while most of the microcontrollers have on-chip interrupt controller.

3. Serial and Parallel ports : The embedded system needs to interface with the external devices for which it needs ports for interfacing. The serial ports give an advantage of long distance data transfer at lower costs, while parallel communication gives faster data transfer for shorter distance.

4. Memory : In an embedded system. ROM (Read only memory) is used for storing program or code while RAM (Random Access Memory) is used for storing data. The ROM used is normally the EEPROM (Electrically Erasable and Programmable ROM). Some data which is a constant value is also sometimes stored in ROM instead of RAM. There are flash memories that are high speed memory.

Power Supply, Oscillator and RESET Circuits

1. Power Supply

The power supply provides power to various circuits in the system. The power supply circuit that consists of a transformer, rectifier and regulator is also an important ingredient of the embedded system. Various voltages are required according to the application, most of the microcontrollers require +6V or +3V as Vcc.

Many embedded systems are battery operated. Certain embedded systems use a special technique called as charge pump. They utilize the charge on the bus and hence save power by the use of set of capacitors and diodes.

The capacitors are charged by the signals given on the bus. The capacitors store this charge and is utilized later as a power source. It can be used to change the voltage. It is very effective for applications where low power usage is required.

2. Oscillator : Some Microcontroller have on chip oscillator and only crystal is to be connected externally or entire oscillator circuit is external. Generally oscillator circuit generates clock pulses for internal operations to be synchronized. But 8051 has on chip oscillator and needs external clock to run it.

8051 has 2 pins XTAL1 and XTAL2, it is connected to Quartz crystal and 30pf capacitors C1 and C2, which forms a resonating network. Operating frequency and crystal frequency is same ranging from 1 to 16 Mhz.

3. Reset Circuit : The Reset pin for 8051 microcontroller is active HIGH. Whenever power is switched ON. Positive going pulse should be present for two machine cycles on this pin. The Reset pin can also be considered as an interrupt as its signal cannot be blocked.