
63
μ
PD75237
(4)
Basic interval timer operation
The basic interval timer (BT) is always incremented by clocks from the clock generator and sets the interrupt
request flag (IRQBT) due to an overflow. BT count operation cannot be stopped.
Four interrupt generate intervals are available by setting the BTM (refer to
Fig. 4-24 Basic Interval Timer
Mode Register Format
).
The basic interval timer and the interrupt request flag can be cleared by setting bit 3 of the BTM (1) (interval
timer start instruction).
The count state can be read from the basic interval timer (BT) by the 8-bit manipulation instruction. Data
cannot be written to the BT.
Note
When reading the basic interval timer count contents, execute the read instruction twice and compare the
two read contents so as not to read unstable data undergoing count update. If the two values are both
acceptable, use the second read value as the correct one. If they differ completely, execute reading again
from the beginning.
To obtain the oscillation stabilize time from STOP mode release to system clock oscillation stabilization,
the wait function is available to stop CPU operation until the basic interval timer overflows.
Wait time after RESET input is fixed, however, if the STOP mode has been released by interrupt generation,
the wait time can be selected by BTM setting. In that case, the wait time is equal to the interval time shown
in Fig. 4-24.
BTM setting must be done before STOP mode setting. (For details, refer to
6 . STANDBY FUNCTIONS
.)
4.5
TIMER/EVENT COUNTER
(1)
Timer/event counter functions
The timer/event counter has the following functions.
(a)
(b)
(c)
(d)
(e)
(f)
Program interval timer operation
Output of square wave with any frequency to PTO0 pin
Event counter operation
Output of N-divided TI0 pin input to PTO0 pin (frequency divider operation)
Serial shift clock supply to the serial interface circuit
Count state read function