AT90PWM216-16SE ATMEL [ATMEL Corporation], AT90PWM216-16SE Datasheet - Page 36

• Manufacturer Part Number: AT90PWM216-16SE
• Description: 8-bit Microcontroller with 16K Bytes In-System Programmable flash
• Manufacturer: ATMEL [ATMEL Corporation]

7.7
7.8
7.9
36
128 kHz Internal Oscillator
External Clock
Clock Output Buffer
AT90PWM216/316
The 128 kHz internal Oscillator is a low power Oscillator providing a clock of 128 kHz. The fre-
quency is nominal at 3V and 25°C. This clock is used by the Watchdog Oscillator.
To drive the device from an external clock source, XTAL1 should be driven as shown in
7-4. To run the device on an external clock, the CKSEL Fuses must be programmed to “0000”.
Figure 7-4.
Table 7-8.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table
Table 7-9.
When applying an external clock, it is required to avoid sudden changes in the applied clock fre-
quency 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. It is required to ensure that the
MCU is kept in Reset during such changes in the clock frequency.
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
37
When the CKOUT Fuse is programmed, the system Clock will be output on CLKO. This mode is
suitable when chip clock is used to drive other circuits on the system. The clock will be output
also during reset and the normal operation of I/O pin will be overridden when the fuse is pro-
grammed. Any clock source, including internal RC Oscillator, can be selected when CLKO
CKSEL3..0
0000
SUT1..0
for details.
00
01
10
11
7-9.
Start-up Time from Power-
External Clock Drive Configuration
External Clock Frequency
Start-up Times for the External Clock Selection
down and Power-save
6 CK
6 CK
6 CK
External
Signal
Clock
Frequency Range
0 - 16 MHz
NC
Additional Delay from
Reset (V
Reserved
14CK + 4.1 ms
14CK + 65 ms
14CK
CC
= 5.0V)
“System Clock Prescaler” on page
XTAL2
XTAL1
GND
BOD enabled
Fast rising power
Slowly rising power
Recommended Usage
7710D–AVR–08/09
Figure