UPD784938 Datasheet, PDF (386/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 12 TIMER 3
(4) While an instruction that writes data to the compare register (CR30) is executed, match between CR30, to which the
data is to be written, and timer counter 3 (TM3) is not detected.
Write data to CR30 when timer 3 is executing count operation so that the contents of TM3 do not match the value of
CR30 before and after writing (e.g., immediately after an interrupt request has been generated because TM3 and CR30
have matched).
(5) Match between TM3 and compare register (CR30) is detected only when TM3 is incremented. Therefore, the interrupt
request is not generated even if the same value as TM3 is written to CR30.
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Preliminary User’s Manual U13987EJ1V0UM00