NEC 10.4 Watch Timer Operations

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CHAPTER 10 WATCH TIMER
10.4 Watch Timer Operations
10.4.1 Watch timer operation
When the 32.768-kHz subsystem clock or 4.19-MHz main system clock is used, the timer operates as a watch
timer with a 0.5-second or 0.25-second interval.
The watch timer sets the test input flag (WTIF) to 1 at the constant time interval. The standby state (STOP mode/
HALT mode) can be cleared by setting WTIF to 1.
When bit 2 (TMC22) of the watch timer mode control register (TMC2) is set to 0, the 5-bit counter is cleared and
the count operation stops.
For simultaneous operation of the interval timer, zero-second start can be achieved by setting TMC22 to 0
(maximum error: 26.2 ms when operated at fXX = 5.0 MHz).
10.4.2 Interval timer operation
The watch timer operates as interval timer which generates interrupt requests repeatedly at an interval of the preset
count value.
The interval time can be selected with bits 4 to 6 (TMC24 to TMC26) of the watch timer mode control register.
Table 10-3. Interval Timer Interval Time
When operated at When operated at When operated at
fXX = 5.0 MHz fXX = 4.19 MHz fXT = 32.768 kHz
000 2
4
× 1/fW410 µ s 488 µ s 488 µ s
001 2
5
× 1/fW819 µ s 977 µ s 977 µ s
010 2
6
× 1/fW1.64 ms 1.95 ms 1.95 ms
011 2
7
× 1/fW3.28 ms 3.91 ms 3.91 ms
100 2
8
× 1/fW6.55 ms 7.81 ms 7.81 ms
101 2
9
× 1/fW13.1 ms 15.6 ms 15.6 ms
Other than above Setting prohibited
Remark fXX : Main system clock frequency (fX or fX/2)
fX: Main system clock oscillation frequency
fXT : Subsystem clock oscillation frequency
fW: Watch timer clock frequency (fXX/27 or fXT)
TMC26 TMC25 TMC24 Interval Time