ATMEGA640 datasheet(46/436 Pages) MICROCHIP

46 / 436 page

ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

10.9 External Clock

To drive the device from an external clock source, XTAL1 should be driven as shown in Figure 10-4. To run the

device on an external clock, the CKSEL Fuses must be programmed to “0000”.

Figure 10-4. External Clock Drive Configuration

When this clock source is selected, start-up times are determined by the SUT Fuses as shown in Table 10-15 on

page 49.

When applying an external clock, it is required to avoid sudden changes in the applied clock frequency to ensure

stable operation of the MCU. A variation in frequency of more than 2% from one clock cycle to the next can lead to

unpredictable behavior. If changes of more than 2% is required, ensure that the MCU is kept in Reset during the

changes.

Note that the System Clock Prescaler can be used to implement run-time changes of the internal clock frequency

while still ensuring stable operation. Refer to “System Clock Prescaler” on page 47 for details.

Table 10-12. Start-up Times for the 128kHz Internal Oscillator

Power Conditions

Start-up Time from Power-down and

Power-save

Additional Delay from Reset

SUT1:0

BOD enabled

6CK

14CK

Fast rising power

6CK

14CK + 4ms

Slowly rising power

6CK

14CK + 64ms

Reserved

Table 10-13. Crystal Oscillator Clock Frequency

Nominal Frequency

CKSEL3:0

0 - 16MHz

0000

Table 10-14. Start-up Times for the External Clock Selection

Power Conditions

Start-up Time from Power-down and

Power-save

Additional Delay from Reset

(VCC = 5.0V)

SUT1:0

BOD enabled

6CK

14CK

Fast rising power

6CK

14CK + 4.1ms

Slowly rising power

6CK

14CK + 65ms

Reserved

EXTERNAL

CLOCK

SIGNAL

XTAL2

XTAL1

GND

ATMEGA640 датащи(PDF) 46 Page - Microchip Technology

ATMEGA640 датащи(HTML) 46 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL