M38002M4 Datasheet, PDF (34/173 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

HARDWARE
FUNCTIONAL DESCRIPTION
Timers
The 3800 group has four timers: timer X, timer Y, timer 1, and timer
2.
All timers are count down. When the timer reaches “0016”, an un-
derflow occurs at the next count pulse and the corresponding
timer latch is reloaded into the timer and the count is continued.
When a timer underflows, the interrupt request bit corresponding
to that timer is set to “1”.
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.
b7
b0
Timer XY mode register
(TM : address 002316)
Timer X operating mode bit
b1b0
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: Interrupt at falling edge
Count at rising edge in event
counter mode
1: Interrupt at rising edge
Count at falling edge in event
counter mode
Timer X count stop bit
0: Count start
1: Count stop
Timer Y operating mode bit
b5b4
0 0: Timer mode
0 1: Pulse output mode
1 0: Event counter mode
1 1: Pulse width measurement mode
CNTR1 active edge switch bit
0: Interrupt at falling edge
Count at rising edge in event
counter mode
1: Interrupt at rising edge
Count at falling edge in event
counter mode
Timer Y count stop bit
0: Count start
1: Count stop
Timer 1 and Timer 2
The count source of prescaler 12 is the oscillation frequency di-
vided by 16. The output of prescaler 12 is counted by timer 1 and
timer 2, and a timer underflow sets the interrupt request bit.
Timer X and Timer Y
Timer X and Timer Y can each be selected in one of four operating
modes by setting the timer XY mode register.
Timer Mode
The timer counts f(XIN)/16 in timer mode.
Pulse Output Mode
Timer X (or timer Y) counts f(XIN)/16. Whenever the contents of
the timer reach “0016”, the signal output from the CNTR0 (or
CNTR1) pin is inverted. If the CNTR0 (or CNTR1) active edge
switch 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 P54 ( or port P55) direction register to out-
put mode.
Event Counter Mode
Operation in event counter mode is the same as in timer mode,
except the timer counts signals input through the CNTR0 or
CNTR1 pin.
Pulse Width Measurement Mode
If the CNTR0 (or CNTR1) active edge selection bit is “0”, the timer
counts at the oscillation frequency divided by 16 while the CNTR0
(or CNTR1) pin is at “H”. If the CNTR0 (or CNTR1) active edge
switch bit is “1”, the count continues during the time that the
CNTR0 (or CNTR1) pin is at “L”.
In all of these modes, the count can be stopped by setting the
timer X (timer Y) count stop bit to “1”. Every time a timer
underflows, the corresponding interrupt request bit is set.
Fig. 15 Structure of timer XY register
1-20
3800 GROUP USER’S MANUAL