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M30245 Group
2.2.11 Operation of Timer A (pulse width modulation mode, 8-bit PWM mode selected)
In pulse width modulation mode, choose functions from those listed in Table 2.2.11. Operations of the
circled items are described below. Figure 2.2.25 shows the operation timing, and Figures 2.2.26 and
2.2.27 show the set-up procedure.
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Operation
Note
Count source (Note 1)
Count start flag
TA
iIN
Underflow signal of 8-bit
prescaler (Note 2)
PWM pulse output from
TA
iOUT
Timer Ai interrupt
request bit
Figure 2.2.25. Operation timing of pulse width modulation mode, with 8-bit PWM mode selected
Rev.2.00 Oct 16, 2006
REJ09B0340-0200
Table 2.2.11. Choosed functions
Item
Count source
O
Internal count source (f
PWM mode
16-bit PWM
O
8-bit PWM
Count start condition
O
External trigger input (falling edge of input signal to the TAi
External trigger input (rising edge of input signal to the TAi
Timer overflow (TAj/TAk overflow)
Note: j = i – 1, but j = 4 when i = 0; k = i + 1, but k = 0 when i = 4.
(1) If the TAi
pin input level changes from "H" to "L" with the count start flag set to "1", the counter
IN
performs a down count on the count source. Also, the TAi
(2) The TAi
pin output level changes from "H" to "L" when a set time period elapses. At this
OUT
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
TAi
pin outputs an "L" level.
OUT
• The period of PWM pulses becomes (m + 1) X (2
becomes n X (m + 1) / fi. If "00
pulse width modulator does not work, and the the TAi
(fi : frequency of the count source f
• 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.
• Set TAi
pin's port direction register to "0".
IN
Conditions:
Reload register high-order 8 bits = 02
Reload register low-order 8 bits = 02
External trigger (falling edge of TAi
"1"
"0"
(1) Start count
"H"
pin input
"L"
"H"
"L"
"H"
pin
"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 = 00
to FE
16
page 31 of 354
/ f
/ f
/ fc
1
8
32
" is set in the eight higher-order bits of the timer Ai register, the
16
, f
, f
, fc
; n : value of the timer)
1
8
32
32
16
16
pin input signal) is selected
IN
1 / f
X (m + 1) X (2 – 1)
i
(2) Output level "H" to "L"
1 / f
X (m+1)
i
1 / f
X (m + 1) X n
i
Cleared to "0" when interrupt request
is accepted, or cleared by software
; n = 00
to FE
.
16
16
16
Set-up
)
32
pin)
IN
pin)
IN
pin outputs an "H" level.
OUT
8
– 1) / fi, and the "H" level pulse width
pin output level remains at "L".
OUT
(4) Stop count
8
(3)
One period is
complete
2. Timer A
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