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Chapter 4 Timer Functions
63
8-bit Timer Operation (timers 2, 3)
4-2-2 Operation
■ Timer Operation (timers 2, 3)
Settings for timer operation are listed below. Timer 2 is used as an example.
(1) Set the TM2EN flag of the timer 2 mode register (TM2MD) to "0" to stop the count
operation of timer 2.
(2) Set the TM2CK2 0 flags of the TM2MD register to select fs, fs/4, fx, or
synchronized fx as the clock source.
(3) Set the TM2PWM flag of the TM2MD register to "0" so that normal timer operation
is selected.
(4) Set a value in compare register 2 (TM2OC).
(5) Set the TM2EN flag of the TM2MD register to "1" to start the timer.
(6) When timer 2 begins operation, binary counter 2 (TM2BC) will count upward from
X'00'.
(7) When the value of binary counter 2 matches that of the TM2OC register, the timer 2
interrupt request flag is set, and the binary counter 2 is reset to X'00' and begins to
count upward again.
Figure 4-2-1 Binary Counter 2 (TM2BC) Count Timing
When servicing an interrupt, reset
the timer 2 interrupt request flag
before starting timer 2.
During a count operation, be
careful if the value set in TM2OC
is smaller than the value of binary
counter 2, since the count-up
operation will continue until
overflow occurs.
If fx is to be selected as the clock
source and the value of binary
counter 2 is to be read during
operation, select synchronized fx
in order to avoid reading data that
may be incomplete during count-
up transitions. However, with
synchronized fx, it is not possible
to return from STOP/HALT modes.
Clock
TM4EN
Binary
counter 4
Write to registers
TM4OCH, TM4OCL
0504 06 07 08 09 00
If the TM2EN flag of TM2MD register is changed simultaneously with
other bits, the switching operation may cause binary counter 2 to be
incremented.
If the value of TM2OC register is overwritten while timer 2 has
stopped counting, binary counter 2 will be reset to X'00' at the edge
of next count clock.
The value of TM3CK0~2 of T3MD register is unsettled. If timer2/
timer 3 is independently used, any mode except cascade
connection should be set.