AT90CAN128-16AE ATMEL Corporation, AT90CAN128-16AE Datasheet - Page 41

• Manufacturer Part Number: AT90CAN128-16AE
• Description: 8-bit Avr Microcontroller With 128K Bytes of Isp Flash And CAN Controller.flash (Kbytes) 128 Vcc (V) 2.7-5.5 EEPROM (Kbytes) 4 SRAM (bytes) 4K CAN (mess. Obj.) 15
• Manufacturer: ATMEL Corporation

External Clock
Clock Output Buffer
4250C–CAN–03/04
To drive the device from an external clock source, XTAL1 should be driven as shown in
Figure 21. To run the device on an external clock, the CKSEL Fuses must be pro-
grammed to “0000”.
Figure 21. External Clock Drive Configuration
Table 14. External Clock Frequency
When this clock source is selected, start-up times are determined by the SUT Fuses as
shown in Table 15.
Table 15. Start-up Times for the External Clock Selection
When applying an external clock, it is required to avoid sudden changes in the applied
clock frequency 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 “System Clock
Prescaler” on page 42 for details.
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 programmed. Any clock source, including internal RC Oscillator, can be
selcted when CLKO serves as clock output. If the System Clock Prescaler is used, it is
the divided system clock that is output (CKOUT Fuse programmed).
CKSEL3..0
0000
SUT1..0
00
01
10
11
Start-up Time from Power-
down and Power-save
6 CK
6 CK
6 CK
External
Signal
Clock
NC
Frequency Range
0 - 16 MHz
Additional Delay from
Reset (V
Reserved
14CK + 4.1 ms
14CK + 65 ms
14CK
CC
= 5.0V)
XTAL2
XTAL1
GND
AT90CAN128
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
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