NEC 78014Y Series User Manual page 198

(6) OVF0 flag operation
OVF0 flag is set to 1:
When clear & start mode on match between TM0 and CR00 is selected
CR00 is set to FFFFH
TM0 is counted up from FFFFH to 0000H
Count Pulse
INTTM00
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198
CHAPTER 8 16-BIT TIMER/EVENT COUNTER
↓
↓
Figure 8-23. OVF0 Flag Operation Timing
CR00 FFFFH
TM0 FFFEH
OVF0
FFFFH 0000H 0001H