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ATMEGA128 датащи(PDF) 55 Page - ATMEL Corporation |
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ATMEGA128 датащи(HTML) 55 Page - ATMEL Corporation |
55 / 386 page 55 2467R–AVR–06/08 ATmega128 Voltage Reference Enable Signals and Start-up Time The voltage reference has a start-up time that may influence the way it should be used. The start-up time is given in Table 20. To save power, the reference is not always turned on. The ref- erence is on during the following situations: 1. When the BOD is enabled (by programming the BODEN fuse). 2. When the bandgap reference is connected to the Analog Comparator (by setting the ACBG bit in ACSR). 3. When the ADC is enabled. Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user must always allow the reference to start up before the output from the Analog Comparator or ADC is used. To reduce power consumption in Power-down mode, the user can avoid the three conditions above to ensure that the reference is turned off before entering Power-down mode. Watchdog Timer The Watchdog Timer is clocked from a separate On-chip Oscillator which runs at 1 Mhz. This is the typical value at V CC = 5V. See characterization data for typical values at other VCC levels. By controlling the Watchdog Timer prescaler, the Watchdog Reset interval can be adjusted as shown in Table 22 on page 57. The WDR – Watchdog Reset – instruction resets the Watchdog Timer. The Watchdog Timer is also reset when it is disabled and when a Chip Reset occurs. Eight different clock cycle periods can be selected to determine the reset period. If the reset period expires without another Watchdog Reset, the ATmega128 resets and executes from the Reset Vector. For timing details on the Watchdog Reset, refer to page 54. To prevent unintentional disabling of the Watchdog or unintentional change of time-out period, 3 different safety levels are selected by the Fuses M103C and WDTON as shown in Table 21. Safety level 0 corresponds to the setting in ATmega103. There is no restriction on enabling the WDT in any of the safety levels. Refer to “Timed Sequences for Changing the Configuration of the Watchdog Timer” on page 58 for details. Table 20. Internal Voltage Reference Characteristics Symbol Parameter Min Typ Max Units VBG Bandgap reference voltage 1.15 1.23 1.40 V tBG Bandgap reference start-up time 40 70 µs IBG Bandgap reference current consumption 10 µA |
Аналогичный номер детали - ATMEGA128 |
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Аналогичное описание - ATMEGA128 |
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