Renesas 4514 - Manual (Page 135)

APPLICATION
2.3 Timers
2-32 4513/4514 Group User’s Manual
Fig. 2.3.3 Constant period measurement setting example
g0 h
0
b3 b0
➀ Disable Interrupts
Timer 1 interrupt is temporarily disabled.
Interrupt enable flag INTE
Interrupt control register V1
“0”
✕ ✕ ✕
All interrupts disabled (DI instruction)
Timer 1 interrupt occurrence disabled
(TV1A instruction)
b3 b0
0 1
➁ Stop Timer Operation
Timer 1 and prescaler are temporarily stopped.
Dividing ratio of prescaler is selected.
Timer control register W1 ✕
Timer 1 stop (TW1A instruction)
Prescaler stop
Prescaler divided by 16 selected
0
➂ Set Timer Value
Timer 1 count time is set. (The formula is shown ❈ A below.)
Timer 1 reload register R1 “F9 16 ” Timer count value 249 set (T1AB instruction)
➃ Clear Interrupt Request
Timer 1 interrupt activated condition is cleared.
Timer 1 interrupt request flag T1F “0” Timer 1 interrupt activated condition cleared
(SNZT1 instruction)
Note when the interrupt request is cleared
When ➃ is executed, considering the skip of the next instruction according to the
interrupt request flag T1F, insert the NOP instruction after the SNZT1 instruction.
➄ Start Timer 1 Operation
Timer 1 and prescaler temporarily stopped are restarted.
Timer 1 operation start (TW1A instruction)
Prescaler operation start
b3 b0
1 1 Timer control register W1 ✕ 1
b3 b0
1
➅ Enable Interrupts
The timer 1 interrupt which is temporarily disabled is enabled.
Interrupt control register V1
Interrupt enable flag INTE “1”
Timer 1 interrupt occurrence enabled
(TV1A instruction)
All interrupts enabled (EI instruction)
✕ ✕ ✕
Constant period interrupt execution start
❈ A 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) ✕ 3 ✕ 16 ✕ (249+1)
–1
System clock Instruction
clock
Prescaler
dividing
ratio Timer 1
count
value
“ ✕ ”: it can be “0” or “1.”