ATTINY817-MFR. datasheet(77/492 Pages) MICROCHIP

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12.3

Functional Description

12.3.1

Initialization

The Reset Controller (RSTCTRL) is always enabled, but some of the Reset sources must be enabled

(either by fuses or by software) before they can request a Reset.

After any Reset, the Reset source that caused the Reset is found in the Reset Flag register

(RSTCTRL.RSTFR).

After a Power-On Reset, only the POR flag will be set.

The flags are kept until they are cleared by writing a '1' to them.

After reset from any source, all registers that are loaded from fuses are reloaded.

12.3.2

Operation

12.3.2.1 Reset Sources

There are two kind of sources for Resets:

•

Power supply Resets, which are caused by changes in the power supply voltage: Power-on Reset

(POR) and Brownout Detector (BOD).

•

User Resets, which are issued by the application, by debug operation or by pin changes (Software

Reset, Watchdog Reset, UPDI Reset and external Reset pin RESET).

Power-On Reset (POR)

A power-on-reset (POR) is generated by an on-chip detection circuit. The POR is activated when the VDD

rises until it reach the POR treshold voltage. The POR is always enabled and will also detect when the

VDD falls below the treshold voltage.

All logic is reset on POR. All fuses are reloaded after the reset is released. While POR is active, TCD pin

override functionality is not available.

Brownout Detector (BOD) Reset Source

The on-chip Brown-out Detection circuit will monitor the VDD level during operation by comparing it to a

fixed trigger level. The trigger level for the BOD can be selected by fuses. If BOD is unused in application

it is forced on to a minimum level in order to guarantee safe operation during internal reset and chip

erase.

All logic is reset on BOD reset, except TCD pin override settings and BOD configuration. All fuses are

reloaded after the reset is released.

ATTINY817-MFR. Datasheet(PDF) 77 Page - Microchip Technology