
3874 Group User's Manual
3-58
APPENDIX
3.5 Control Registers
Fig. 3.5.21 Structure of timer 123 mode register
Timer 123 mode register
b7 b6 b5 b4 b3 b2 b1 b0
Timer 123 mode register
(T123M: address 2916)
b
0
Name
0
Functions
At reset R W
TOUT output active
edge switch bit
0 : Start at “H” output
1 : Start at “L” output
1
0
TOUT output control
bit
0 : TOUT output disabled
1 : TOUT output enabled
2
0
Timer 2 write
control bit
0 : Write data in latch and
counter at one time
1 : Write data in latch only
3
0
Timer 2 count source
selection bit
0 : Timer 1 output
1 : f(XIN)/16
(or f(XCIN)/16 in low-
speed mode) (Note)
4
0
Timer 3 count source
selection bit
0 : Timer 1 output
1 : f(XIN)/16
(or f(XCIN)/16 in low-
speed mode) (Note)
5
0
Timer 1 count source
selection bit
1 : f(XIN)/16
(or f(XCIN)/16 in low-
speed mode) (Note)
0 : f(XCIN)
7
0
6
0
Nothing is arranged for these bits. These are write
disabled bits. When these bits are read out, the
contents are “0”.
Note 1 : In the low-speed mode, the internal clock
φ is XIN pin input
signal divided by 2.
2 : In case of the following, a short pulse occurs on counted input
signals, so that the timer count value may change greatly.
Accordingly, after setting their count sources, set values in
order of timer 1, timer 2, and timer 3 following:
When the count sources of timers 1 to 3 are switched
When the timer 1 output signal is selected as a count source
of timer 2 or timer 3 and data is written to timer 1
3 : In the TOUT output enabled state of timer 2, a signal whose
polarity is reversed each time timer 2 underflows is output
from the TOUT pin. In this case, set port P50 (sharing with the
TOUT pin) to the output mode.
4 : In stop mode
Set the interrupt enabled bits of timer 1 and timer 2 to the
disabled state (“0”) before executing the STP instruction.
Oscillation restarts at reset or when an external interrupt is
received, but the internal clock
φ is not supplied to the CPU
until timer 2 underflows. It is because that retains time to
stabilize oscillation using a ceramic resonator, etc. Set
values for stabilizing oscillation to the timer 1 latch and timer
2 latch before executing the STP instruction.