MC68336/376
CONFIGURABLE TIMER MODULE 4
MOTOROLA
USER’S MANUAL
Rev. 15 Oct 2000
10-18
10.9.9 PWM Pulse Width
The shortest output pulse width (tPWMIN) that can be obtained is given by the following
equation:
The maximum output pulse width (tPWMAX) that can be obtained is given by the follow-
ing equation:
10.9.10 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:
10.9.10.1 PWM Duty Cycle Boundary Cases
PWM duty cycles 0% and 100% are special boundary cases (zero pulse width and infi-
nite 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 10-6 PWM Pulse and Frequency Ranges (in Hz) Using ÷ 3 Option (20.97 MHz)
fsys
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
s
107
224
427
853
1707
3413
6826
13652
27305
54609
109K
218K
437K
874K
1748K
3495K
÷ 6
0.358
s
53
107
224
427
853
1707
3413
6826
13652
27305
54609
109K
218K
437K
874K
1748K
÷ 12
0.715
s
27
53
107
224
427
853
1707
3413
6826
13652
27305
54609
109K
218K
437K
874K
÷ 24
1.431
s
13
27
53
107
224
427
853
1707
3413
6826
13652
27305
54609
109K
218K
437K
÷ 48
2.861
s
7
13
27
53
107
224
427
853
1707
3413
6826
13652
27305
54609
109K
218K
÷ 96
5.722
s
3
7
13
27
53
107
224
427
853
1707
3413
6826
13652
27305
54609
109K
÷ 192
11.44
s
2
3
7
13
27
53
107
224
427
853
1707
3413
6826
13652
27305
54609
÷ 768
45.78
s
0.4
0.8
2
3
7
13
27
53
107
224
427
853
1707
3413
6826
13652
t
PWMIN
N
CLOCK
f
sys
--------------------
=
t
PWMAX
N
CLOCK
N
PERIOD
1
–
()
f
sys
-------------------------------------------------------------
=
PWMA1
f
sys
N
CLOCK
f
PWM
-------------------------------------
=
PWMB1
1
t
PWMIN
f
PWM
----------------------------------
Duty Cycle %
100
------------------------------------ PWMA1
==