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ATmega128-16AU Scheda tecnica(PDF) 40 Page - ATMEL Corporation |
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ATmega128-16AU Scheda tecnica(HTML) 40 Page - ATMEL Corporation |
40 / 386 page 40 2467S–AVR–07/09 ATmega128 Notes: 1. These options should only be used when not operating close to the maximum frequency of the device, and only if frequency stability at start-up is not important for the application. These options are not suitable for crystals. 2. These options are intended for use with ceramic resonators and will ensure frequency stability at start-up. They can also be used with crystals when not operating close to the maximum fre- quency of the device, and if frequency stability at start-up is not important for the application. Low-frequency Crystal Oscillator To use a 32.768 kHz watch crystal as the clock source for the device, the Low-frequency Crystal Oscillator must be selected by setting the CKSEL fuses to “1001”. The crystal should be con- nected as shown in Figure 19. By programming the CKOPT fuse, the user can enable internal capacitors on XTAL1 and XTAL2, thereby removing the need for external capacitors. The inter- nal capacitors have a nominal value of 36 pF. When this Oscillator is selected, start-up times are determined by the SUT fuses as shown in Table 10. Note: 1. These options should only be used if frequency stability at start-up is not important for the application. Table 9. Start-up Times for the Crystal Oscillator Clock Selection CKSEL0 SUT1..0 Start-up Time from Power-down and Power-save Additional Delay from Reset (V CC = 5.0V) Recommended Usage 0 00 258 CK(1) 4.1 ms Ceramic resonator, fast rising power 0 01 258 CK(1) 65 ms Ceramic resonator, slowly rising power 0 10 1K CK(2) – Ceramic resonator, BOD enabled 0 11 1K CK(2) 4.1 ms Ceramic resonator, fast rising power 1 00 1K CK(2) 65 ms Ceramic resonator, slowly rising power 1 01 16K CK – Crystal Oscillator, BOD enabled 1 10 16K CK 4.1 ms Crystal Oscillator, fast rising power 1 11 16K CK 65 ms Crystal Oscillator, slowly rising power Table 10. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection SUT1..0 Start-up Time from Power-down and Power-save Additional Delay from Reset (V CC = 5.0V) Recommended Usage 00 1K CK(1) 4.1 ms Fast rising power or BOD enabled 01 1K CK(1) 65 ms Slowly rising power 10 32K CK 65 ms Stable frequency at start-up 11 Reserved |
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