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12. Timer
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12.1.4. Pulse Width Modulation (PWM) Mode
In PWM mode, the timer outputs pulses of a given width in succession (see Table 12.1.4.1). The counter
functions as either 16-bit pulse width modulator or 8-bit pulse width modulator. Figure 12.1.4.1 shows
TAiMR register in pulse width modulation mode. Figures 12.1.4.2 and 12.1.4.3 show examples of how a
16-bit pulse width modulator operates and how an 8-bit pulse width modulator operates.
Table 12.1.4.1. Specifications in Pulse Width Modulation Mode
Item
Specification
Count source
f1, f2, f8, f32, fC32
Count operation
Down-count (operating as an 8-bit or a 16-bit pulse width modulator)
The timer reloads a new value at a rising edge of PWM pulse and continues counting
The timer is not affected by a trigger that occurs during counting
16-bit PWM
High level width
n / fj
n : set value of TAi register (i=o to 4)
Cycle time (216-1) / fj fixed
fj: count source frequency (f1, f2, f8, f32, fC32)
8-bit PWM
High level width
n x (m+1) / fj n : set value of TAi register high-order address
Cycle time
(28-1) x (m+1) / fj
m : set value of TAi register low-order address
Count start condition
TAiS bit in theTABSR register is set to “1” (= start counting)
The TAiS bit is set to "1" and external trigger input from the TAiIN pin
The TAiS bit is set to "1" and one of the following external triggers occurs
Timer B2 overflow or underflow,
timer Aj (j=i-1, except j=4 if i=0) overflow or underflow,
timer Ak (k=i+1, except k=0 if i=4) overflow or underflow
Count stop condition
TAiS bit is set to “0” (= stop counting)
Interrupt request generation timing
PWM pulse goes “L”
TAiIN pin function
I/O port or trigger input
TAiOUT pin function
Pulse output
Read from timer
An indeterminate value is read by reading TAi register
Write to timer
When not counting and until the 1st count source is input after counting start
Value written to TAi register is written to both reload register and counter
When counting (after 1st count source input)
Value written to TAi register is written to only reload register
(Transferred to counter when reloaded next)