CHAPTER 10 INTERVAL TIMER, WATCH TIMERUser’s Manual U16896EJ2V0UD34410.2.4 Operation(1) Operation as watch timerThe watch timer generates an interrupt request at fixed time intervals.The watch timer operates using time intervals of 0.25 or 0.5 seconds with the subclock (32.768 kHz).The count operation starts when the WTM.WTM0 and WTM.WTM1 bits are set to 11. When these bits arecleared to 00, the 11-bit prescaler and 5-bit counter are cleared and the count operation stops.The 5-bit counter can be cleared to synchronize the time by clearing the WTM1 bit to 0 when the watch timerand interval timer WT operate simultaneously. At this time, an error of up to 15.6 ms may occur in the watchtimer, but interval timer WT is not affected.(2) Operation as interval timerThe watch timer can also be used as an interval timer that repeatedly generates an interrupt request signal(INTWTI) at intervals specified by a count value set in advance.The interval time can be selected by the WTM.WTM4 to WTM.WTM7 bits.Table 10-1. Interval Time of Interval TimerWTM7 WTM6 WTM5 WTM4 Interval Time0 0 0 0 2 4× 1/f W 488μs (operating at f W = f XT = 32.768 kHz)0 0 0 1 2 5 × 1/f W 977μs (operating at f W = f XT = 32.768 kHz)0 0 1 0 2 6 × 1/f W 1.95 ms (operating at f W = f XT = 32.768 kHz)0 0 1 1 2 7× 1/f W 3.91 ms (operating at f W = f XT = 32.768 kHz)0 1 0 0 2 8 × 1/f W 7.81 ms (operating at f W = f XT = 32.768 kHz)0 1 0 1 2 9 × 1/f W 15.6 ms (operating at f W = f XT = 32.768 kHz)0 1 1 0 2 10× 1/f W 31.3 ms (operating at f W = f XT = 32.768 kHz)0 1 1 1 2 11 × 1/f W 62.5 ms (operating at f W = f XT = 32.768 kHz)1 0 0 0 2 4 × 1/f W 488μs (operating at f W = f BRG = 32.768 kHz)1 0 0 1 2 5× 1/f W 977μs (operating at f W = f BRG = 32.768 kHz)1 0 1 0 2 6 × 1/f W 1.95 ms (operating at f W = f BRG = 32.768 kHz)1 0 1 1 2 7 × 1/f W 3.91 ms (operating at f W = f BRG = 32.768 kHz)1 1 0 0 2 8× 1/f W 7.81 ms (operating at f W = f BRG = 32.768 kHz)1 1 0 1 2 9× 1/f W 15.6 ms (operating at f W = f BRG = 32.768 kHz)1 1 1 0 2 10 × 1/f W 31.3 ms (operating at f W = f BRG = 32.768 kHz)1 1 1 1 2 11× 1/f W 62.5 ms (operating at f W = f BRG = 32.768 kHz)Remark f W: Watch timer clock frequency
