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ATMEGA8515 Datasheet(PDF) 35 Page - ATMEL Corporation |
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ATMEGA8515 Datasheet(HTML) 35 Page - ATMEL Corporation |
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35 / 257 page  35 ATmega8515(L) 2512K–AVR–01/10 Flash Clock – clk FLASH The Flash clock controls operation of the Flash interface. The Flash clock is usually active simultaneously with the CPU clock. 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 6. The frequency of the Watchdog Oscil- lator is voltage dependent as shown in “ATmega8515 Typical Characteristics” on page 207. Default Clock Source The device is shipped with CKSEL = “0001” and SUT = “10”. The default clock source setting is therefore the Internal RC Oscillator with longest start-up time. This default set- ting ensures that all users can make their desired clock source setting using an In- System or Parallel Programming. Crystal Oscillator XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be configured for use as an On-chip Oscillator, as shown in Figure 19. Either a quartz crystal or a ceramic resonator may be used. The CKOPT Fuse selects between two dif- ferent 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 operat- ing 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 Table 5. 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 6. 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. - ATMEGA8515_10 |
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Similar Description - ATMEGA8515_10 |
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