Embedded processor: It is the heart of the embedded system. It has two essential units : control unit and execution unit. Control unit fetches instructions from memory and execution unit includes ALU and circuits to perform execution of the instructions for a program control task
Power supply, reset & oscillator circuit:
Most of the systems have their own power supply. Some embedded systems do not have their own power supply. These embedded systems are powered by external power supply e.g. USB based embedded system, network interface card, Graphics Accelerator etc. are powered by PC power supply.
Reset means that processor begins processing of instructions from starting address set by default in program counter on power up.
The clock circuit controls execution time of instructions, CPU machine cycles.
Timers: Timer circuit is suitably configured as system clock or RTC (Real time clock). To schedule various tasks and for real time programming an RTC (Real Time Clock), or system clock is needed.
Program & data memory: In embedded system, secondary memory like disk is avoided. Most of the embedded processors have internal memory such as ROM, RAM, flash/EEPROM, EPROM/PROM for storing program and data.
Interrupt controller: It is an interrupt handling mechanism which must exist in embedded system to handle interrupts from various processes and for handling multiple interrupts simultaneously pending for service.
I/O ports: I/O ports are used to interface external devices like sensors, key buttons, transducers, LEDs, LCD actuators, alarms, motors, values, printer etc. There are two types of ports, parallel and serial port. The parallel ports are used in short distance communication while serial ports are used in long distance communication.
Input& output device interfacing/driver circuits: Some I/O devices like motors, actuators, valves, sensors are not compatible with the processor. Hence the I/O interface circuits are designed to drive such input and output devices interfaced to the embedded processor
System Application specific circuits: These are the circuits that can control specific target circuits. They consist of ADC, DAC, relays, sensors etc.