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CHAPTER 9 8-BIT TIMER/EVENT COUNTERS 2, 3 TM2, TM3
9.5 8-Bit Timer/Event Counters 2 and 3 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 n (TMn) is started asynchronously with the count pulse.
Figure 9-10. Timer n Start Timing
Count pulse
TMn count value
00H
01H
02H
03H
04H
Timer start
n = 2, 3
(2) Operation after compare register change during timer count operation
If the values after the 8-bit compare register n (CRn) is changed are smaller than the value of 8-bit timer register
n (TMn), TMn continues counting, overflows and then restarts counting from 0. Thus, if the value (M) after CRn
change is smaller than value (N) before the change, it is necessary to restart the timer after changing CRn.
Figure 9-11. Timing after Compare Register Change during Timer Count Operation
Count pulse
CRn
TMn count value
N
M
X–1
X
FFH
00H
01H
02H
Remarks 1.
N > X > M
2.
n = 2, 3
Caution Except when the TIOn input is selected, always set TCEn = 0 before setting the STOP state.
Remark
n = 2, 3
(3) TMn (n = 2, 3) reading during timer operation
When TMn is read during operation, choose a select clock which has a longer high/low level wave because the
select clock is stopped temporarily.
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