ATA6617 View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
ATA6617
Atmel Corporation
'ATA6617' PDF : 308 Pages View PDF
When the CPU wakes up from Power-down or Power-save, or when a new clock source is
enabled by the dynamic clock switch circuit, 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 an additional delay allowing the power to reach a sta-
ble level before commencing normal operation. The Watchdog Oscillator is used for timing this
real-time part of the start-up sequence. The number of WDT Oscillator cycles used for each
time-out is shown in Table 4-6.
4.5.2.1
4.5.2.2
Table 4-6. Number of Watchdog Oscillator Cycles
Typ. Time-out (Vcc = 5.0V)
Typ. Time-out (Vcc = 5.0V)
4.1ms
4.3ms
65ms
69ms
Number of Cycles
512
8K (8,192)
Default Clock Source
At reset, the CKSEL and SUT fuse settings are copied into the CLKSELR register. The device
will then use the clock source and the start-up timings defined by the CLKSELR bits
(CSEL3..0 and CSUT1:0).
The device is shipped with CKSEL Fuses = 0010 b, SUT Fuses = 10 b, and CKDIV8 Fuse pro-
grammed. The default clock source setting is therefore the Internal RC Oscillator running at 8
MHz with the longest start-up time and an initial system clock divided by 8. This default setting
ensures that all users can make their desired clock source setting using an In-System or
High-voltage Programmer. This set-up must be taken into account when using ISP tools.
Calibrated Internal RC Oscillator
By default, the Internal RC Oscillator provides an approximate 8.0 MHz clock. Though voltage
and temperature dependent, this clock can be accurately calibrated by the user. See Table
4-81 on page 269 and Section 4.25.7 “Internal Oscillator Speed” on page 288 for more details.
If selected, it can operate without external components. At reset, hardware loads the pre-pro-
grammed calibration value into the OSCCAL Register and thereby automatically configuring
the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in Table
4-81 on page 269.
By adjusting the OSCCAL register in software, see Section 4.5.5.1 “OSCCAL – Oscillator Cal-
ibration Register” on page 61, 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 269.
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-pro-
grammed calibration value, see the section Section 4.22.4 “Calibration Byte” on page 252.
50 Atmel ATA6616/ATA6617
9132D–AUTO–12/10
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