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ETM12E-01
3) Overview of fixed-cycle timer interrupt function
(1) Changing the TE (Timer Enable) bit value from "0" to "1" starts operation of the fixed-cycle timer
interrupt function.
∗ Before starting the fixed-cycle timer interrupt function each time, be sure to write a value (preset
value/Reg-0F[h]) as the down counter value for the timer (when TE = "0").
(Note) Note with caution that the preset value must be set or reset to enable correct operation.
(2) When the TE bit = "1", the timer's down counter (Timer Register/Reg − 0F[h]) counts down once per
cycle (countdown cycle) of the source clock that was selected via the TD1 and TD0 bits (Timer
countdown interval select bits 1 and 0).
∗ Timer cycle (Period) = Source clock × value (preset value) set to timer's down counter
(3) The following processing is executed after an event is triggered by the countdown reaching a count
value of "0".
∗1) The TF (Timer Flag) bit value becomes "1".
∗2) When the TIE (Timer Interrupt Enable) bit value becomes "1", the /INT output pin's status changes
from Hi-z to "L".
∗ After the /INT output pin's status changes from Hi-z to "L", the /INT status is either held at low
level or automatically cleared, depending on the TI/TP bit's setting from the operation mode
(level interrupt mode or repeated interrupt mode).
∗3) The timer's down counter automatically returns to the preset value and then the countdown
operation is repeated.
∗ When the TE bit value is "1", countdown operation of the timer's down counter will be repeated
regardless of the operation mode or of any event that has occurred.
(4) When the TE bit is cleared from "1" to 0", the fixed-cycle timer interrupt function stops.
∗1) The TF bit value remains "1" until it is cleared to zero (even if the fixed-cycle timer function has been
stopped).
∗2) The timer's down counter value becomes invalid once the fixed-cycle timer function has been
stopped.
∗ When the fixed-cycle timer interrupt function is stopped, the timer's down counter value and the
preset value both become invalid.
∗ The preset value must be written again (when TE = "0") in order to start the fixed-cycle timer
interrupt function again.
∗ Operation example
∗ Operation example during repeated interrupt mode and when preset value is "5" (05h).
Period
TE-bit
(
Timer Enable
)
" 1 "
(Timer function is ON
)
Timer's down counter
(Timer Register)
Fixed-cycle timer
interrupt
Internal event occurs at
(
)
part
5
4 3 2 1
0
5
4321
0
5
4321
0
5
∗ When the TE-bit is changed to "1", the
countdown starts from the preset value, which is
"5" (05h) in this example.
4
3
" 0 "
(Timer function is OFF )
Period Period
∗
Countdown is stopped
∗
Count value and preset
value are invalid.
Source
clock
/INT output
(Open drain output)
∗
When TIE = "1"
output is at low level only during tRTN
period.