at90pwm81-16se ATMEL Corporation, at90pwm81-16se Datasheet - Page 29

• Manufacturer Part Number: at90pwm81-16se
• Description: 8-bit Avr Microcontroller With 8k Bytes In- System Programmable Flash
• Manufacturer: ATMEL Corporation

Table 6-1.
6.2.1
6.2.2
7734M–AVR–03/10
Device Clocking Option
External Crystal/Ceramic Resonator (3.0 - 8.0 MHz)
External Crystal/Ceramic Resonator (3.0 - 8.0 MHz)
External Crystal/Ceramic Resonator (8.0 - 16.0 MHz)
External Crystal/Ceramic Resonator (8.0 - 16.0 MHz)
Default Clock Source
Calibrated Internal RC Oscillator
Device Clocking Options Select
Note:
The various choices for each clocking option is given in the following sections.
When the CPU wakes up from Power-down, 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 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 6-2.
The device will always starts up from reset using the clock source defined by CKSEL Fuses the start-up
time defined by SUT Fuses. This configuration is latched in CLKSELR register at reset. The device will
always starts up at Power-on using the clock source defined by CLKSELR register (CSEL3..0 and
CSUT1:0).
The device is shipped with CKSEL Fuses = 0010
The default clock source setting is therefore the Internal RC Oscillator running at 8 MHz with longest
start-up time and an initial system clock prescaling of 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.
By default, the Internal RC OScillator provides an approximate 8.0 MHz clock or a 1 MHz clock. Though
voltage and temperature dependent, this clock can be very accurately calibrated by the user.
1. For all fuses “1” means unprogrammed while “0” means programmed.
2. PLL must be driven by a nominal 8 MHz clock source
3. Flash Fuse bits.
4. CLKSELR register bits.
5. Ext Osc : External Osc
6. RC Osc : Internal RC Oscillator (1 MHz or 8 MHz)
7. WD : Internal Watch Dog RC Oscillator 128 kHz
8. Ext Clk : External Clock Input
Typ. Time-out
Number of Watchdog Oscillator Cycles
(1)
64 ms
4 ms
, PLL source and PE1 and PE2 functionality
System
Clock
Ext Osc
Ext Osc
Ext Osc
Ext Osc
PLL Input
RC Osc
RC Osc
RC Osc
RC Osc
b
, SUT Fuses = 10
(2)
CKSEL3..0
CSEL3..0
1100
1101
1110
1111
Number of Cycles
b
b
b
b
b
8K (8,192)
, and CKDIV8 Fuse programmed.
(4)
(3)
512
AT90PWM81
XTAL1
XTAL1
XTAL1
XTAL1
PE1
Table
XTAL2
XTAL2
XTAL2
XTAL2
PE2
6-2.
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