24
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
3827 Group
MITSUBISHI MICROCOMPUTERS
Timer 1, Timer 2, Timer 3
Timer 1, timer 2, and timer 3 are 8-bit timers. The count source for
each timer can be selected by timer 123 mode register. The timer
latch value is not affected by a change of the count source. How-
ever, because changing the count source may cause an
inadvertent count down of the timer. Therefore, rewrite the value of
timer whenever the count source is changed.
G
Timer 2 write control
If the timer 2 write control bit is “0”, when the value is written in the
address of timer 2, the value is loaded in the timer 2 and the latch
at the same time.
If the timer 2 write control bit is “1”, when the value is written in the
in the latch is loaded in timer 2 after timer 2 underflows.
G
Timer 2 output control
When the timer 2 (T
OUT
) is output enabled, an inversion signal
from the T
OUT
pin is output each time timer 2 underflows.
In this case, set the port shared with the T
OUT
pin to the output.
I
Notes on timer 1 to timer 3
When the count source of timer 1 to 3 is changed, the timer count-
ing value may be changed large because a thin pulse is generated
in count input of timer . If timer 1 output is selected as the count
source of timer 2 or timer 3, when timer 1 is written, the counting
value of timer 2 or timer 3 may be changed large because a thin
pulse is generated in timer 1 output.
Therefore, set the value of timer in the order of timer 1, timer 2 and
timer 3 after the count source selection of timer 1 to 3.
Fig. 20 Structure of timer 123 mode register
T
OUT
output active edge switch bit
0 : Start at “H” output
1 : Start at “L” output
T
OUT
/
φ
output control bit
0 : T
OUT
/
φ
output disabled
1 : T
OUT
/
φ
output enabled
Timer 2 write control bit
0 : Write data in latch and counter
1 : Write data in latch only
Timer 2 count source selection bit
0 : Timer 1 output
1 : f(X
IN
)/16
(or f(X
CIN
)/16 in low-speed mode)
Timer 3 count source selection bit
0 : Timer 1 output
1 : f(X
IN
)/16
(or f(X
CIN
)/16 in low-speed mode)
Timer 1 count source selection bit
0 : f(X
IN
)/16
(or f(X
CIN
)/16 in low-speed mode)
1 : f(X
CIN
)
Not used (return “0” when read)
Timer 123 mode register
(T123M :address 0029
16
)
Note :
Internal clock
φ
is X
CIN
/2 in the low-speed mode.
b7
b0