6.1 Basic connecting
As seen in the figure above, in order to enable the microcontroller to operate properly it is necessary to provide:
- Power supply:
- Reset signal: and
- Clock signal.
Clearly, it is about very simple circuits, but it does not have to be always like that. If the target device is used for controlling expensive machines or maintaining vital functions, everything gets increasingly complicated. However, this solution is sufficient for the time being...
Even though this microcontroller can operate at different power supply voltages, why to test “Murphy’s low”?! A 5V DC is most commonly used. The circuit, shown in the figure, uses a cheap integrated three-terminal positive regulator LM7805, and provides high-quality voltage stability and quite enough current to enable the microcontroller and peripheral electronics to operate normally (enough current in this case means 1Amp).
In order that the mucrocontroller can operate properly, a logic 0 (0V) must be applied to the reset pin RS. The push button connecting the reset pin RS to power supply VCC is not necessary. However, it is almost always provided because it enables the microcontroller safe return to normal operating conditions if something goes wrong. 5V is brought to this pin, the microcontroller is reset and program starts execution from the beginning.
Even though the microcontroller has a built-in oscillator, it cannot operate without two external capacitors and quartz crystal which stabilize its operation and determines its frequency (operating speed of the microcontroller).
Of course, it is not always possible to apply this solution so that there are always alternative ones. One of them is to provide clock signal from a special source through invertor. See the figure on the left.