4518 Datasheet, PDF (72/160 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4518 Group
12 Watchdog timer
• The watchdog timer function is valid after system is released
from reset. When not using the watchdog timer function, execute
the DWDT instruction and the WRST instruction continuously,
and clear the WEF flag to “0” to stop the watchdog timer func-
tion.
• The watchdog timer function is valid after system is returned
from the RAM back-up state. When not using the watchdog timer
function, execute the DWDT instruction and the WRST instruc-
tion continuously every system is returned from the RAM
back-up state, and stop the watchdog timer function.
• When the watchdog timer function and RAM back-up function are
used at the same time, execute the WRST instruction before
system enters into the RAM back-up state and initialize the flag
13 Prescaler, Timer 1, Timer 2 and Timer 3 count start timing and
count time when operation starts
Count starts from the first rising edge of the count source (2) af-
ter Prescaler, Timer 1, Timer 2 and Timer 3 operations start (1).
Time to first underflow (3) is shorter (for up to 1 period of the
count source) than time among next underflow (4) by the timing
to start the timer and count source operations after count starts.
(2)
Count Source
Timer value 3 2 1 0 3 2 1 0 3 2
Timer Underflow signal
(3)
(4)
(1) Timer Start
Fig. 63 Timer count start timing and count time when opera-
tion starts (Prescaler, Timer 1, Timer 2 and Timer 3)
14 _{Timer 4 count start timing and count time when operation starts}
Count starts from the rising edge (2) after the first falling edge of
the count source, after Timer 4 operations start (1).
Time to first underflow (3) is different from time among next un-
derflow (4) by the timing to start the timer and count source
operations after count starts.
(2)
Count Source
Timer Value
32 1 0 3 2 1 0 3
Timer Underflow Signal
(3)
(4)
(1) Timer Start
Fig. 64 Timer count start timing and count time when opera-
tion starts (Timer 4)
Rev.3.01 2005.06.15 page 72 of 157
REJ03B0008-0301