ATAM862 datasheet(23/110 Pages) ATMEL

23 / 110 page

4554E–4BMCU–05/06

ATAM862-3

17. Master Reset

The master reset forces the CPU into a well-defined condition. It is unmaskable and is activated

independent of the current program state. It can be triggered by either initial supply power-up, a

short collapse of the power supply, brown-out detection circuitry, watchdog time-out, or an exter-

nal input clock supervisor stage (see Figure 17-1). A master reset activation will reset the

interrupt enable flag, the interrupt pending register and the interrupt active register. During the

power-on reset phase, the I/O bus control signals are set to reset mode, thereby, initializing all

on-chip peripherals. All bi-directional ports are set to input mode

Attention: During any reset phase, the BP20/NTE input is driven towards V

DD by an additional

internal strong pull-up transistor. This pin must not be pulled down to V

SS during reset by any

external circuitry representing a resistor of less than 150 k

Ω.

Releasing the reset results in a short call instruction (opcode C1h) to the ROM address 008h.

This activates the initialization routine $RESET which in turn has to initialize all necessary RAM

variables, stack pointers and peripheral configuration registers (see Table 21-1 on page 34).

Figure 17-1. Reset Configuration

17.1

Power-on Reset and Brown-out Detection

The microcontroller block has a fully integrated power-on reset and brown-out detection circuitry.

For reset generation no external components are needed.

These circuits ensure that the core is held in the reset state until the minimum operating supply

voltage has been reached. A reset condition will also be generated should the supply voltage

drop momentarily below the minimum operating level except when a power-down mode is acti-

vated (the core is in SLEEP mode and the peripheral clock is stopped). In this power-down

mode the brown-out detection is disabled.

Two values for the brown-out voltage threshold are programmable via the BOT bit in the

SC register.

Reset

timer

Power-on

reset

Internal

reset

res

CL=SYSCL/4

Brown-out

detection

Watch-

dog

CWD

res

Ext. clock

supervisor

ExIn

Pull-up

NRST

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