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CHAPTER 8 8-BIT TIMER 1 TM1
8.5 8-Bit Timer 1 Cautions
(1) Timer start errors
An error with a maximum of one clock may occur concerning the time required for a match signal to be generated
after timer start. This is because 8-bit counter 1 (TM1) is started asynchronously with the count pulse.
Figure 8-5. Timer 1 Start Timing
Count pulse
TM1 count value
00H
01H
02H
03H
04H
Timer start
(2) Operation after compare register change during timer count operation
If the values after the 8-bit compare register 1 (CR1) is changed are smaller than the value of 8-bit timer register
1 (TM1), TM1 continues counting, overflows and then restarts counting from 0. Thus, if the value (M) after CR1
change is smaller than value (N) before the change, it is necessary to restart the timer after changing CR1.
Figure 8-6. Timing after Compare Register Change during Timer Count Operation
Count pulse
CR1
TM1 count value
N
M
X–1
X
FFH
00H
01H
02H
Remark
N > X > M
Caution Always set TCE1 = 0 before setting the STOP state.
(3) TM1 reading during timer operation
When TM1 is read during operation, choose a count clock which has a longer high/low level wave because 8-
bit counter (TM1) is stopped temporary.
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