NEC V850E/PH2 User Manual page 510

(4) Overflow flag
When, in the free-running mode, the counter overflows from FFFFH to 0000H, the overflow flag
(TTnOVF) is set to "1", and an overflow interrupt (INTTTnOV) is output.
The overflow flag is cleared through 0 write from the CPU.
(The overflow flag is not cleared by just being read.)
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Chapter 11 16-bit Timer/Event Counter T
User's Manual U16580EE3V1UD00