NEC uPD78056Y - Manual (Page 214)

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CHAPTER 8 16-BIT TIMER/EVENT COUNTER
Count Pulse
CR00
TM0
OVF0
INTTM00
FFFFH
FFFEH FFFFH 0000H 0001H
(7) Operation of OVF0 flag
OFV0 flag is set to 1 in the following case.
The clear & start mode on match between TM0 and CR00 is selected.
↓
CR00 is set to FFFFH.
↓
When TM0 is counted up from FFFFH to 0000H.
Figure 8-38. Operation Timing of OVF0 Flag