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| AT43USB320A_04 Datasheet, PDF (23/115 Pages) ATMEL Corporation – Full-speed USB Microcontroller with an Embedded Hub | |||
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Figure 6. Reset Logic
USB Reset
AT43USB320A
VCC
POR Ckt
RSTN
Reset Ckt
Watchdog Timer
System Clock
Divider
OR
14-bit Cntr
S
ON
Cntr Reset
FSTRT
R
Power-on Reset
Table 7. Number of Watchdog Oscillator Cycles
FSTRT
Programmed
Time-out at VCC = 5V
1.1 ms
Unprogrammed
16.0 ms
Number of WDT cycles
1K
16K
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 VCC has reached the power-on threshold voltage, regardless of the VCC
rise time.
If the build-in start-up delay is sufficient, RESET can be connected to VCC directly or via an
external pull-up resistor. By holding the pin low for a period after VCC has been applied, the
Power-on Reset period can be extended.
23
1443EâUSBâ4/04
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