ATA6612C View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
ATA6612C
Atmel Corporation
'ATA6612C' PDF : 312 Pages View PDF
5.6.5
Low Frequency Crystal Oscillator
The device can utilize a 32.768kHz watch crystal as clock source by a dedicated low frequency crystal oscillator. The crystal
should be connected as shown in Figure 5-12. When this oscillator is selected, start-up times are determined by the SUT
fuses and CKSEL0 as shown in Table 5-10.
Table 5-10. Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
Power Conditions
BOD enabled
Start-up Time from Power-
down and Power-save
1kCK
Additional Delay from
Reset (VCC = 5.0V)
14CK(1)
CKSEL0
0
SUT1..0
00
Fast rising power
1kCK
14CK + 4.1ms(1)
0
01
Slowly rising power
1kCK
14CK + 65ms(1)
0
10
Reserved
0
11
BOD enabled
32kCK
14CK
1
00
Fast rising power
32kCK
14CK + 4.1ms
1
01
Slowly rising power
32kCK
14CK + 65ms
1
10
Reserved
1
11
Note: 1. These options should only be used if frequency stability at start-up is not important for the application.
5.6.6
Calibrated Internal RC Oscillator
The calibrated internal RC oscillator by default provides a 8.0MHz clock. The frequency is nominal value at 5V and 25°C.
The device is shipped with the CKDIV8 fuse programmed. See Section 5.6.11 “System Clock Prescaler” on page 54 for more
details. This clock may be selected as the system clock by programming the CKSEL fuses as shown in Table 5-11. If
selected, it will operate with no external components. During reset, hardware loads the calibration byte into the OSCCAL
register and thereby automatically calibrates the RC oscillator. At 5V and 25°C, this calibration gives a frequency of 8MHz
±1%. The tolerance of the internal RC oscillator remains better than ±10% within the whole automotive temperature and
voltage ranges (4.5V to 5.5V, –40°C to +125°C). The oscillator can be calibrated to any frequency in the range 7.3 - 8.1MHz
within ±1% accuracy, by changing the OSCCAL register. When this oscillator is used as the chip clock, the watchdog
oscillator will still be used for the watchdog timer and for the reset time-out. For more information on the pre-programmed
calibration value (see Section 5.24.4 “Calibration Byte” on page 256).
Table 5-11. Internal Calibrated RC Oscillator Operating Modes(1)(3)
Frequency Range(2) (MHz)
CKSEL3..0
7.3 - 8.1
Notes: 1. The device is shipped with this option selected.
0010
2. The frequency ranges are preliminary values. Actual values are TBD.
3. If 8MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8 fuse can be
programmed in order to divide the internal frequency by 8.
ATA6612C/ATA6613C [DATASHEET]
51
9111L–AUTO–11/14
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