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• The Reset Pin

The Reset Pin

Occasionally computer software gets itself into such a mess that the only sensible thing to do is to "reboot" the system. Microprocessors have an input connection called RESET(or something similar) that when activated initialises the processor and starts it running in a predetermined and safe fashion.

Whenever a logical low is detected on the ARM RESET, the program counter is reinitialized to 0x00000000 and the processor begins execution of the instructions found there.

The RESET input is normally used in two circumstances:

• A reset button can be connected that brings the RESET pin voltage to 0 V and hence restarts the microprocessor. This is useful for emergency reboots.
• When the power is switched on, suitable circuitry can ensure that the RESET pin voltage is held at 0 V for a short period so that the microprocessor starts up in a predefined state.

Reset circuit

The values of R and C must be set such that VC does not rise above 2 V too quickly. The critical time depends on how long it takes the processor to initiate the reset sequence.