Subject : Embedded Systems Design

Topic : Fundamentals of Embedded System

Difficulty level : Low

• The reset pin of a microcontroller is either active high or active low.
• Let us consider 8051 microcontroller.
• The reset pin of 8051 active high. Whenever power is switched on, positive going pulse should be present for 2 machine cycles on this pin.

• Reset Circuit for microcontroller 8051 is as follows:

  

• At t0, the power supply is switched on, the supply voltage Vcc appears across the RC network. The entire voltage across resistor R, so VR is approximately equal to Vcc. This resets the 8051 microcontroller.
• Once the capacitor charges, then VR start decreasing and reach approximately 0V. This removes the reset signal. The (t1-t0) is reset time.