ATA6617C_14 Datasheet, PDF (48/274 Pages) ATMEL Corporation – 8K/16K Flash Microcontroller with LIN Transceiver, 5V Regulator and Watchdog

4.5.2.2 Calibrated Internal RC Oscillator
By default, the internal RC oscillator provides an approximate 8.0MHz clock. The frequency is nominal at 5V and 25°C.
Though voltage and temperature dependent, this clock can be accurately calibrated by the user.
See Table 4-81 on page 239 and Section 4.25.7 “Internal Oscillator Speed” on page 254 for more details.
If selected, it can operate without external components. At reset, hardware loads the pre-programmed calibration value into
the OSCCAL register and thereby automatically configuring 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 accuracy of this calibration is shown as factory
calibration in Table 4-81 on page 239.
By adjusting the OSCCAL register in software, see Section 4.5.5.1 “OSCCAL – Oscillator Calibration Register” on page 58,
it is possible to get a higher calibration accuracy than by using the factory calibration. The accuracy of this calibration is
shown as User calibration in Table 4-81 on page 239.
The watchdog oscillator will still be used for the watchdog timer and for the reset time-out even when this oscillator is used
as the device clock. For more information on the pre-programmed calibration value,
see the section Section 4.22.4 “Calibration Byte” on page 224.
Table 4-7. Internal Calibrated RC Oscillator Operating Modes⁽¹⁾
Frequency Range⁽²⁾ (MHz)
CKSEL3..0⁽³⁾⁽⁴⁾
CSEL3..0⁽⁵⁾
7.6 - 8.4
0010
Notes: 1. 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
2. The frequency ranges are guideline values
3. The device is shipped with this CKSEL = “0010”
4. Flash Fuse bits.
5. CLKSELR register bits
When this oscillator is selected, start-up times are determined by the SUT fuses or by CSUT field as shown in Table 4-8.
Table 4-8. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
SUT1..0⁽¹⁾
CSUT1..0⁽²⁾
Start-up Time from
Power-down/save
Additional Delay from Reset
(Vcc = 5.0V)
00⁽³⁾
6 CK
14CK
01
6 CK
14CK + 4.1ms
10⁽⁴⁾
6 CK
14CK + 65ms
11
Notes: 1. Flash fuse bits
Reserved
2. CLKSELR register bits
3. This setting is only available if RSTDISBL fuse is not set
4. The device is shipped with this option selected
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
48 ATA6616C/ATA6617C [DATASHEET]
9132I–AUTO–06/14