Timer A
Mitsubishi microcomputers
M16C / 62 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
306
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 TAiIN pin)
External trigger input (rising edge of input signal to the TAiIN pin)
Timer overflow (TB2/TAj/TAk overflow)
Table 2.2.12. Choosed functions
Note: j = i – 1, but j = 4 when i = 0; k = i + 1, but k = 0 when i = 4.
(1) If the TAiIN 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 TAiOUT pin outputs an “H” level.
(2) The TAiOUT pin output level changes from “H” to “L” when a set time period elapses. At this
time, the timer Ai 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
TAiOUT pin outputs an “L” level.
The period of PWM pulses becomes (m + 1) X (28 – 1) / fi, and the “H” level pulse width
becomes n X (m + 1) / fi. If “0016” is set in the eight higher-order bits of the timer Ai register, the
pulse width modulator does not work, and the the TAiOUT pin output level remains at “L”.
(fi : frequency of the count source f1, f8, f32, fc32; n : value of the timer)
When a trigger is generated, the TAiout pin outputs “L” level of same amplitude as “H” level of
the set PWM pulse, after which it starts PWM pulse output.
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 TAiIN pin input signal) is selected
1 / fi X (m + 1) X (2 – 1)
8
TAiIN pin input
Underflow signal of 8-bit
prescaler (Note 2)
PWM pulse output from
TAiOUT pin
“H”
“L”
Timer Ai 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 FE16; n = 0016 to FE16.
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