AT43USB326 datasheet(21/102 Pages) ATMEL

21 / 102 page

AT43USB326

3313D–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 6 shows the reset logic. The user

can select the start-up time according to typical oscillator start-up. The number of WDT oscilla-

tor cycles used for each time-out is shown in Table 7.

Figure 6. 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, RESET 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

System Clock

Table 7. Number of Watchdog Oscillator Cycles

FSTRT

Time-out at V

CC = 5V

Number of WDT cycles

Programmed

1.1 ms

Unprogrammed

16.0 ms

16K

AT43USB326 数据表(PDF) 21 Page - ATMEL Corporation

AT43USB326 数据表(HTML) 21 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载