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VI - 17
Chapter 6 8-bit Timers
8-bit Timer Count
6-3-2 Setup Example
Timer Operation Setup Example (Timers 0, 1, 4 and 5)
Timer function can be set by using timer 0 that generates the constant interrupt. By selecting fs/4 (at fosc
= 20 MHz) as a clock source, interrupt is generated every 250 clock cycles (100 µs).
An example setup procedure, with a description of each step is shown below.
(1) Set the TM0EN flag of the timer 0 mode
register (TM0MD) to "0" to stop the counting of
timer 0.
(2) Set the TM0PWM flag and TM0MOD flag of
the TM0MD register to "0" to select the normal
timer operation.
(3) Select the prescaler output to the clock source
by the TM0CK2-0 flag of the TM0MD register.
(4) Select fs/4 to the prescaler output by the
TM0PSC1-0, TM0BAS flag of the timer 0
prescaler selection register (CK0MD).
Also, set the PSCEN flag of the prescaler
control register (PSCMD) to "1" to enable the
counting of the prescaler.
(5) Set the value of the interrupt generation cycle
to the timer 0 compare register (TM0OC). The
cycle is 250, so that the setting value is set to
249 (x'F9').
At that time, the timer 0 binary counter
(TM0BC) is initialized to x'00'.
(6) Set the interrupt level by the TM0LV1-0 flag of
the timer 0 interrupt control register (TM0ICR).
If the interrupt request flag may be already set,
clear the request flag.
[ Chapter 3 3-1-4. Interrupt flag setting ]
Setup Procedure
(1) Stop the counter.
TM0MD (x'3F54')
bp3 :TM0EN = 0
(2) Select the normal timer operation.
TM0MD (x'3F54')
bp4 :TM0PWM = 0
bp5 :TM0MOD = 0
(3) Select the count clock source.
TM0MD (x'3F54')
bp2-0 :TM0CK2-0 = 001
(4) Select the prescaler output and
enable the counting.
CK0MD (x'3F56')
bp2-1 :TM0PSC1-0 = 01
bp0 :TM0BAS = 1
PSCMD (x'3F6F')
bp0 :PSCEN = 1
(5) Set the cycle of the interrupt
generation.
TM0OC (x'3F52') = x'F9'
(6) Set the interrupt level.
TM0ICR (x'3FE9')
bp7-6 :TM0LV1-0 = 10
Description