
MC68HC16R1/916R1
USER’S MANUAL
CONFIGURABLE TIMER MODULE 7
MOTOROLA
12-19
12.10.9 PWM Pulse Width
The shortest output pulse width (t
PWMIN
) that can be obtained is given by the following
equation:
The maximum output pulse width (t
PWMAX
) that can be obtained is given by the follow-
ing equation:
12.10.10 PWM Period and Pulse Width Register Values
The value loaded into PWMA1 to obtain a given period is:
The value loaded into PWMB1 to obtain a given duty cycle is:
12.10.10.1 PWM Duty Cycle Boundary Cases
PWM duty cycles 0% and 100% are special boundary cases (zero pulse width and in-
finite pulse width) that are defined by the “always clear” and “always set” states of the
output flip-flop.
A zero width pulse is generated by setting PWMB2 to $0000. The output is a true
steady state signal. An infinite width pulse is generated by setting PWMB2 equal to or
greater than the period value in PWMA2. In both cases, the state of the output pin will
remain unchanged at the polarity defined by the POL bit in PWMSIC.
Table 12-7 PWM Pulse and Frequency Ranges (in Hz) Using
÷
3 Option (16.78 MHz)
f
Divide
Ratio
Minimum
Pulse
Width
Bits of Resolution
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
÷
3
0.179
μ
s
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k
87.38k
174.8k
349.5k
699.1k
1398k
2796k
÷
6
0.358
μ
s
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k
87.38k
174.8k
349.5k
699.1k
1398k
÷
12
0.715
μ
s
21.33
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k
87.38k
174.8k
349.5k
699.1k
÷
24
1.431
μ
s
10.67
21.33
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k
87.38k
174.8k
349.5k
÷
48
2.861
μ
s
5.333
10.67
21.33
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k
87.38k
174.8k
÷
96
5.722
μ
s
2.667
5.333
10.67
21.33
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k
87.38k
÷
192
11.44
μ
s
1.333
2.667
5.333
10.67
21.33
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k
÷
768
45.78
μ
s
0.333
0.667
1.333
2.667
5.333
10.67
21.33
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
t
PWMIN
N
f
sys
-------------------
=
t
PWMAX
N
--------------------------------------------------–
N
f
sys
)
=
PWMA1
f
N
CLOCK
f
PWM
------------------------------------
=
PWMB1
1
t
PWMIN
f
PWM
----------------------------------
Duty Cycle %
100
-----------------------------------
PWMA1
=
=