4513_03 Datasheet, PDF (135/210 Pages) Renesas Technology Corp – 4-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATION
2.3 Timers
ΠDisable Interrupts
Timer 1 interrupt is temporarily disabled.
Interrupt enable flag INTE “0”
All interrupts disabled (DI instruction)
b3
b0 _{Timer 1 interrupt occurrence disabled}
Interrupt control register V1 ! 0 ! ! _{(TV1A instruction)}
 Stop Timer Operation
Timer 1 and prescaler are temporarily stopped.
Dividing ratio of prescaler is selected.
Timer control register W1
b3
0
1
0
b0
!
Timer 1 stop (TW1A instruction)
Prescaler stop
Prescaler divided by 16 selected
Ž Set Timer Value
Timer 1 count time is set. (The formula is shown gA below.)
Timer 1 reload register R1 “F916” Timer count value 249 set (T1AB instruction)
 Clear Interrupt Request
Timer 1 interrupt activated condition is cleared.
Timer 1 interrupt request flag T1F “0” _{g0 h}
Timer 1 interrupt activated condition cleared
(SNZT1 instruction)
Note when the interrupt request is cleared
When  is executed, considering the skip of the next instruction according to the
interrupt request flag T1F, insert the NOP instruction after the SNZT1 instruction.
 Start Timer 1 Operation
Timer 1 and prescaler temporarily stopped are restarted.
b3
b0
Timer control register W1 1 1 1 ! ^{Timer 1 operation start (TW1A instruction)}
Prescaler operation start
‘ Enable Interrupts
The timer 1 interrupt which is temporarily disabled is enabled.
Interrupt control register V1
b3
b0
!1 !!
Timer 1 interrupt occurrence enabled
(TV1A instruction)
Interrupt enable flag INTE “1”
All interrupts enabled (EI instruction)
Constant period interrupt execution start
gA The prescaler dividing ratio and timer 1 count value to make the interrupt occur
every 4 ms are set as follows.
4 ms ≅ (4.0 MHz) !^–1 3 ! 16 ! (249+1)
System clock Instruction Prescaler Timer 1
clock
dividing count
ratio
value
“!”: it can be “0” or “1.”
Fig. 2.3.3 Constant period measurement setting example
2-32
4513/4514 Group User’s Manual