12. Timer A
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page 114
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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 12.5). The counter
functions as either 16-bit pulse width modulator or 8-bit pulse width modulator. Figure 12.12 shows
TAiMR register in pulse width modulation mode. Figures 12.13 and 12.14 show examples of how a 16-
bit pulse width modulator operates and how an 8-bit pulse width modulator operates.
Table 12.5 Specifications in Pulse Width Modulation Mode
Item Specification
Count source f1, f2, f8, f32, fC32
Count operation • D
ecrement (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 (2
16
-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 (2
8
-1) x (m+1) / fj m : set value of TAi register low-order address
Count start condition • TAiS bit in the TABSR register is set to 1 (= start counting)
• The TAiS bit = 1 and external trigger input from the TAiIN pin
• The TAiS bit = 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 undefined 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)
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