8-bit AVR Microcontrollers

Power-on Reset

A Power-on Reset (POR) pulse is generated by an on-chip detection circuit. The POR is activated whenever VCC is below the detection level. The POR circuit can be used to trigger the start-up Reset, as well as to detect a failure in supply voltage.

A POR circuit ensures that the device is reset from power-on. Reaching the POR threshold voltage invokes the delay counter, which determines how long the device is kept in Reset after VCC rise. The Reset signal is activated again, without any delay, when VCC decreases below the detection level.

Figure 1. MCU Start-up, RESET Tied to VCC
Figure 2. MCU Start-up, RESET Extended Externally