63
μ
PD75236
(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 stabiliza-
tion, 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)
Program interval timer operation
(b)
Output of square wave with any frequency to PTO0 pin
(c)
Event counter operation
(d)
Output of N-divided TI0 pin input to PTO0 pin (frequency divider operation)
(e)
Serial shift clock supply to the serial interface circuit
(f)
Count state read function