NEC 78K0 Series User Manual page 290

Caution Do not change the count clock and interval time (by setting bits 4 to 7 (WTM4 to WTM7) of WTM)
during watch timer operation.
Remarks 1. f : Watch timer clock frequency (f
W
2. f : Peripheral hardware clock frequency
PRS
3. f : Subsystem clock frequency
SUB
290
CHAPTER 10 WATCH TIMER
7
/2 or f )
PRS SUB
Preliminary User's Manual U17260EJ3V1UD