The structural units of an embedded system can be divided into two parts.

Hardware units 

Software units

Embedded hardware:

Hardware units are more importants in any kinds of embedded system.  It requirement are varied from one system to another system. Some important hardware units is embedded aystem are

1. Power source: Most system have thier own power supply unit and certain systems do not have thier own power source , that system require charge pump                       An internal power source or a charge pump is essential in every system. It has to perform tasks continuously from power up to power off and may event be kept ON continuously.
2. Own power supply system: The system has its own power supply then the supply has a specific operation range or a range of voltages.
3. Charge power supply system:    certain system do not have a own power source such system have external power supply or charge pumps.                                                       Network interface card and graphic accelerator are example of embedded system. That do not have their own power supply and connect to pc power supply lines.    A charge pump consist of a diode in the series followed by a charging capacitor. The diode gets forward bias input from an external signal charge pumps bring the power a non-supply line.                           Clock oscillator circuit and clocking units: The clock is the next important unit of a system. A highly stable oscillator is used for processing units. The processor clock out signal provide the clock for sychronizing. The clock control the various clocking requirement of the CPU system timers. And the machine cycle of CPU and aslo control the time for executing an instruction.                                           The machine cycle are for  1. Fetching codes and data from memory and then decoding and executing at processor 2. Transferring the results to memory. Time for executing an instruction. 3.crystal for external to the processor associated with the processor.                                        
4. An external oscillator IC attached to the processor.                                    REAL TIME CLOCK : A circuit suitably configured is the system clock also called real time clock. An RTC is used by the schedluler and for real time program it also drives the timers for various timing and counting needs in a system. Reset means the peocessor start the processing of instruction from  a starting address. It activates for a fixed period and then deactivates. Reset can be activated by one of the following condition. A aystem boat-up program. A system initialization program.