Hitachi H8/3937 Series Hardware Manual page 226

3. After read timer control status register F (TCSRF), clear timer overflow flags (OVFH,
OVFL) and compare match flags (CMFH, CMFL).
4. Operate interrupt permission (set IENFH, IENFL to 1).
Method 2
1. Set interrupt handling routine time to more than time that calculated with (1) formula.
2. Clear interrupt request flags (IRRTFH, IRRTFL) at the end of interrupt handling routine.
3. After read timer control status register F (TCSRF), clear timer overflow flags (OVFH,
OVFL) and compare match flags (CMFH, CMFL).
All above attentions are also applied in 16-bit mode and 8-bit mode.
Program process
øw
Interrupt factor
generation signal
(Internal signal,
nega-active)
Overflow signal,
Compare match signal
(Internal signal,
nega-active)
Interrupt request flag
(IRRTFH, IRRTFL)
Figure 9-7 Clear Interrupt Request Flag when Interrupt Factor Generation Signal is Valid
4. Timer counter (TCF) read/write
When øw/4 is selected as the internal clock in active (high-speed, medium-speed) mode, write on
TCF is impossible. And, when read TCF, as the system clock and internal clock are mutually
asynchronous, TCF synchronizes with synchronization circuit. This results in a maximum TCF
read value error of ±1.
When read/write TCF in active (high-speed, medium-speed) mode is needed, please select internal
clock except for øw/4 before read/write.
In subactive mode, even øw/4 is selected as the internal clock, normal read/write TCF is possible.
214
Interrupt request
flag clear
2
Interrupt Interrupt
1
Interrupt request
flag clear
Normal