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Timer A
Mitsubishi microcomputers
M30201 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
200
2.2.12 Operation of Timer A (pulse width modulation mode, 8-bit PWM mode selected)
Figure 2.2.26. Operation timing of pulse width modulation mode, with 8-bit PWM mode selected
In pulse width modulation mode, choose functions from those listed in Table 2.2.12. Operations of the
circled items are described below. Figure 2.2.26 shows the operation timing, and Figure 2.2.27 shows the
set-up procedure.
Item
Count source
PWM mode
Count start condition
Set-up
O
Internal count source (f1 / f8 / f32 / fc32)
16-bit PWM
8-bit PWM
External trigger input (falling edge of input signal to the TA0IN pin)
External trigger input (rising edge of input signal to the TA0IN pin)
Timer overflow (TB1/TX0/TX2 overflow)
Table 2.2.12. Choosed functions
(1) If the TA0IN pin input level changes from “H” to “L” with the count start flag set to “1”, the counter
performs a down count on the count source. Also, the TA0OUT pin outputs an “H” level.
(2) The TA0OUT pin output level changes from “H” to “L” when a set time period elapses. At this
time, the timer A0 interrupt request bit goes to “1”.
(3) The counter reloads the content of the reload register every time PWM pulses are output for
one cycle, and continues counting.
(4) Setting the count start flag to “0” causes the counter to hold its value and to stop. Also, the
TA0OUT pin outputs an “L” level.
PWM pulse cycle is (m + 1( x (28 -1)/fi, whereas “H” level duration is n x (m + 1)/fi. However,
when “0016” is set for the significant 8 bits of the timer A0 register, the PWM output is “L” level
for the entire period, and an interrupt request is generated for every PWM output cycle. Also,
when “FF16” is set for the significant 8 bits of the timer A0 register, the PWM output is “H” level
for the entire period, and an interrupt request is generated for every PWM output cycle.
(fi: Count source frequency f1, f8, f32, fC32 n: Timer value)
Operation
Note
Count source (Note 1)
Reload register high-order 8 bits = 0216
Reload register low-order 8 bits = 0216
External trigger (falling edge of TA0IN pin input signal) is selected
1 / fi X (m + 1) X (2 – 1)
8
TA0IN pin input
Underflow signal of 8-bit
prescaler (Note 2)
PWM pulse output from
TA0OUT pin
“H”
“L”
Timer A0 interrupt
request bit
“H”
“L”
“1”
“0”
Note 1: The 8-bit prescaler counts the count source.
Note 2: The 8-bit pulse width modulator counts the 8-bit prescaler's underflow signal.
Note 3: m = 0016 to FF16; n = 0016 to FF16.
1 / fi X (m + 1) X n
Count start flag
“1”
“0”
(1) Start count
(2) Output level “H” to “L”
Cleared to “0” when interrupt request
is accepted, or cleared by software
(3)
(4) Stop count
1 / fi X (m+1)
Conditions:
One period is
complete