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ATmega16-16PU Datasheet(PDF) 25 Page - ATMEL Corporation |
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ATmega16-16PU Datasheet(HTML) 25 Page - ATMEL Corporation |
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25 / 357 page  25 2466S–AVR–05/09 ATmega16(L) ADC Clock – clk ADC The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks in order to reduce noise generated by digital circuitry. This gives more accurate ADC conversion results. Clock Sources The device has the following clock source options, selectable by Flash Fuse bits as shown below. The clock from the selected source is input to the AVR clock generator, and routed to the appropriate modules. Note: 1. For all fuses “1” means unprogrammed while “0” means programmed. The various choices for each clocking option is given in the following sections. When the CPU wakes up from Power-down or Power-save, the selected clock source is used to time the start- up, ensuring stable Oscillator operation before instruction execution starts. When the CPU starts from Reset, there is as an additional delay allowing the power to reach a stable level before commencing normal operation. The Watchdog Oscillator is used for timing this real-time part of the start-up time. The number of WDT Oscillator cycles used for each time-out is shown in Table 3. The frequency of the Watchdog Oscillator is voltage dependent as shown in “ATmega16 Typ- ical Characteristics” on page 299. Default Clock Source The device is shipped with CKSEL = “0001” and SUT = “10”. The default clock source setting is therefore the 1 MHz Internal RC Oscillator with longest startup time. This default setting ensures that all users can make their desired clock source setting using an In-System or Parallel Programmer. Crystal Oscillator XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be con- figured for use as an On-chip Oscillator, as shown in Figure 12. Either a quartz crystal or a ceramic resonator may be used. The CKOPT Fuse selects between two different Oscillator amplifier modes. When CKOPT is programmed, the Oscillator output will oscillate will a full rail- to-rail swing on the output. This mode is suitable when operating in a very noisy environment or when the output from XTAL2 drives a second clock buffer. This mode has a wide frequency range. When CKOPT is unprogrammed, the Oscillator has a smaller output swing. This reduces power consumption considerably. This mode has a limited frequency range and it can not be used to drive other clock buffers. For resonators, the maximum frequency is 8 MHz with CKOPT unprogrammed and 16 MHz with CKOPT programmed. C1 and C2 should always be equal for both crystals and resonators. The optimal value of the capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of the environment. Some initial guidelines for Table 2. Device Clocking Options Select(1) Device Clocking Option CKSEL3..0 External Crystal/Ceramic Resonator 1111 - 1010 External Low-frequency Crystal 1001 External RC Oscillator 1000 - 0101 Calibrated Internal RC Oscillator 0100 - 0001 External Clock 0000 Table 3. Number of Watchdog Oscillator Cycles Typ Time-out (VCC = 5.0V) Typ Time-out (VCC = 3.0V) Number of Cycles 4.1 ms 4.3 ms 4K (4,096) 65 ms 69 ms 64K (65,536) |
Similar Part No. - ATmega16-16PU |
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Similar Description - ATmega16-16PU |
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