參數(shù)資料
型號: AT43USB326-AU
廠商: Atmel Corp.
英文描述: Multimedia USB Keyboard Controller with Embedded Hub
中文描述: 多媒體USB鍵盤控制器的嵌入式集線器
文件頁數(shù): 21/102頁
文件大?。?/td> 511K
代理商: AT43USB326-AU
21
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 V
CC
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
OR
POR Ckt
Reset Ckt
Watchdog Timer
Divider
14-bit Cntr
VCC
RSTN
System Clock
S
R
ON
Table 7.
Number of Watchdog Oscillator Cycles
FSTRT
Time-out at V
CC
= 5V
Number of WDT cycles
Programmed
1.1 ms
1K
Unprogrammed
16.0 ms
16K
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