136
8018P–AVR–08/10
ATmega169P
Enabling and disabling of the clock input must be done when T1/T0 has been stable for at least
one system clock cycle, otherwise it is a risk that a false Timer/Counter clock pulse is generated.
Each half period of the external clock applied must be longer than one system clock cycle to
ensure correct sampling. The external clock must be guaranteed to have less than half the sys-
tem clock frequency (f
ExtClk < fclk_I/O/2) given a 50/50% duty cycle. Since the edge detector uses
sampling, the maximum frequency of an external clock it can detect is half the sampling fre-
quency (Nyquist sampling theorem). However, due to variation of the system clock frequency
and duty cycle caused by Oscillator source (crystal, resonator, and capacitors) tolerances, it is
recommended that maximum frequency of an external clock source is less than f
clk_I/O/2.5.
An external clock source can not be prescaled.
Figure 16-2. Prescaler for Timer/Counter0 and Timer/Counter1
Note:
1. The synchronization logic on the input pins (
T1/T0) is shown in Figure 16-1 on page 135.
PSR10
Clear
clk
T1
clk
T0
T1
T0
clk
I/O
Synchronization
相关PDF资料
2-1546217-0 TERM BLK RCPT 20POS SIDE 5.08MM
1-1546217-9 TERM BLK RCPT 19POS SIDE 5.08MM
1-1546217-8 TERM BLK RCPT 18POS SIDE 5.08MM
1-1546217-7 TERM BLK RCPT 17POS SIDE 5.08MM
1-1546217-6 TERM BLK RCPT 16POS SIDE 5.08MM
1-1546217-5 TERM BLK RCPT 15POS SIDE 5.08MM
1-1546217-4 TERM BLK RCPT 14POS SIDE 5.08MM
1-1546217-3 TERM BLK RCPT 13POS SIDE 5.08MM
相关代理商/技术参数
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