The CPU needs a clock source, and a crystal oscillator generates the clock. The
Crystal is choosing based on the clock frequency of the processor. Micro-controllers
provide an on chip oscillator and you connect an external crystal or ceramic resonator.

The clock generation circuitry determines the various states of machine cycles.

[] Reset Circuit

It is generally built in the hardware to take care of any unforeseen problems. This circuit
handles software handles software hang-ups, power supply failures, etc. The processor
sends a status signal to this circuit periodically. If in case this signal is not received, it is an
indicator that something is wrong, this is then reset by this circuit Single chip solutions are
also available.

Watchdog timer

Most of the embedded systems have no provision of resetting the processor in such
cases a watchdog timer is used. It is set to a large value and is counted down. When value
reaches zero, the processor resets. If things are fine and there is no need to reset the

processor, the processor resets the watchdog timer to that large value again.

‎Chip-select logic circuit‏ لا

‎In the processor-based systems, many digital chips share common bus. To carry out
transaction with a particular chip, the processor must be able to uniquely identify the chip.
The processor performs this identification through a signal called the chip-select- signal.
This signal is available to all devices connected to bus and it is of either high or low level.

‎This signal can be generated using decoder/encoder-multiplexer chip.

‎Application-specific control circuitry‏ تا

‎Since we are dealing with embedded systems which can be application specific so
such circuitry is needed which can handle specific applications. Devices which needed
includes sensor and transducers (to obtain real-world from external sources), relays(to
control external circuitry) and various input devices, such as keyboards, functional
keypads etc. To control all these devices on needs circuitry to interface them with the

‎processor.