38K2 Datasheet, PDF (19/151 Pages) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

38K2 Group
TIMERS
The 38K2 group has three timers: timer X, timer 1, and timer 2.
The division ratio of each timer or prescaler is given by 1/(n + 1),
where n is the value in the corresponding timer or prescaler latch.
All timers are down count timers. When the timer reaches “0016”,
an underflow occurs at the next count pulse and the correspond-
ing timer latch is reloaded into the timer and the count is contin-
ued. When a timer underflows, the interrupt request bit corre-
sponding to that timer is set to “1”.
b7
b0
Timer X mode register
(TM : address 002316)
Timer X operating mode bits
b1 b0
0 0 : Timer mode
0 1 : Pulse output mode
1 0 : Event counter mode
1 1 : Pulse width measurement mode
CNTR0 active edge switch bit
0 : Falling edge active for CNTR0 interrupt
Count at rising edge in event counter mode
1 : Rising edge active for CNTR0 interrupt
Count at falling edge in event counter mode
Timer X count stop bit
0 : Count start
1 : Count stop
Not used (return “0” when read)
Fig. 16 Structure of timer X mode register
Timer 1 and Timer 2
The count source of prescaler 12 is the system clock divided by
16. The output of prescaler 12 is counted by timer 1 and timer 2,
and a timer underflow periodically sets the interrupt request bit.
Timer X
Timer X can each select in one of four operating modes by setting
the timer X mode register.
(1) Timer Mode
The timer counts the count source selected by timer count source
selection bit.
(2) Pulse Output Mode
The timer counts the system clock divided by 16. Whenever the
contents of the timer reach “0016”, the signal output from the
CNTR0 pin is inverted. If the CNTR0 active edge selection bit is
“0”, output begins at “ H”.
If it is “1”, output starts at “L”. When using a timer in this mode, set
the corresponding port P51 direction register to output mode.
(3) Event Counter Mode
Operation in event counter mode is the same as in timer mode,
except that the timer counts signals input through the CNTR0 pin.
When the CNTR0 active edge selection bit is “0”, the rising edge of
the CNTR0 pin is counted.
When the CNTR0 active edge selection bit is “1”, the falling edge
of the CNTR0 pin is counted.
(4) Pulse Width Measurement Mode
If the CNTR0 active edge selection bit is “0”, the timer counts the
system clock divided by 16 while the CNTR0 pin is at “H”. If the
CNTR0 active edge selection bit is “1”, the timer counts it while the
CNTR0 pin is at “L”.
The count can be stopped by setting “1” to the timer X count stop
bit in any mode. The corresponding interrupt request bit is set
each time a timer underflows.
Rev.3.00 Oct 15, 2006 page 19 of 147
REJ03B0193-0300