AT43USB355 datasheet(23/115 Pages) ATMEL

23 / 115 page

AT43USB355

2603G–USB–04/06

When the USB hardware is reset, the compound device is de-configured and has to be re-

enumerated by the host. When the microcontroller is reset, all I/O registers are then set to their

initial values, and the program starts execution from address $000. The instruction placed in

address $000 must be a JMP instruction to the reset handling routine. If the program never

enables an interrupt source, the interrupt vectors are not used, and regular program code can

be placed at these locations. The circuit diagram in Figure 9 shows the reset logic.

Figure 9. Reset Logic

Power-on Reset

A Power-on Reset (POR) circuit ensures that the device is reset from power-on. An internal

timer clocked from the Watchdog timer oscillator prevents the MCU from starting until after a

certain period after V

CC has reached the power-on threshold voltage, regardless of the VCC

rise time.

If the build-in start-up delay is sufficient, RESETN can be connected to V

CC directly or via an

external pull-up resistor. By holding the pin low for a period after V

CC has been applied, the

Power-on Reset period can be extended.

FSTRT

Cntr Reset

USB Reset

POR Ckt

Reset Ckt

Watchdog Timer

Divider

14-bit Cntr

VCC

RSTN

1 MHz Clock

AT43USB355 데이터시트(PDF) 23 Page - ATMEL Corporation