AT43USB355M-AC ATMEL [ATMEL Corporation], AT43USB355M-AC Datasheet - Page 23

• Manufacturer Part Number: AT43USB355M-AC
• Description: Full-speed USB Microcontroller with Embedded Hub, ADC and PWM
• Manufacturer: ATMEL [ATMEL Corporation]

Figure 9. Reset Logic
Power-on Reset
2603G–USB–04/06
1 MHz Clock
RSTN
VCC
Watchdog Timer
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.
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
rise time.
If the build-in start-up delay is sufficient, RESETN can be connected to V
external pull-up resistor. By holding the pin low for a period after V
Power-on Reset period can be extended.
Reset Ckt
POR Ckt
Divider
CC
USB Reset
has reached the power-on threshold voltage, regardless of the V
14-bit Cntr
OR
Cntr Reset
FSTRT
AT43USB355
CC
has been applied, the
S
R
CC
directly or via an
ON
23
CC