8-Bit Timer 1 Cautions - NEC mPD780973 Series Preliminary User's Manual

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.
Count pulse
TM1 count value
(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
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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CHAPTER 8 8-BIT TIMER 1 TM1
Figure 8-5. Timer 1 Start Timing
00H 01H
Timer start
N
X–1 X
02H 03H 04H
M
FFH 00H 01H 02H