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CHAPTER 11 12-bit PWM
11.3 Operation of 12-bit PWM
The 12-bit PWM acquires a 12-bit resolution by inserting added pulse to the output
waveform using the 8-bit and 4-bit counters.
■ Operation of 12-bit PWM
The 12-bit PWM is operated by the 8-bit and 4-bit counters. The 8-bit counter will be the basic frequency
at the time of PWM conversion, and output waveform duty is specified by the duty control-bit of the data
register. In terms of the conversion operation, this is repeated 16 times, and 12-bit resolution is acquired by
inserting an added pulse to the specific position during repeated operation. Insertion position of the added
pulse is specified by the added pulse control bit.
The PWM output waveform will be as Figure 11.3-1 .
Figure 11.3-1 PWM operation waveform
A pulse is added when "1" is specified in accordance with the added pulse control bit value.
1 2 4 5 6 7 8 9 10 1112 13 14 15 16
Convert cycle
Basic frequency
fch/2
8
or fch/2
9
Add Pulse
3
Table 11.3-1 Pulse Insert Position
DATA Insertion position of added pulse
0000
B
----------------
0001
B
--------1 -------
0010
B
----1 -------1 ---
0011
B
----1 ---1 ---1 ---
0100
B
--1 ---1 ---1 ---1 -
0101
B
--1 ---1 -1 -1 ---1 -
0110
B
--1 -1 -1 ---1 -1 -1 -
0111
B
--1 -1 -1 -1 -1 -1 -1 -
1000
B
-1 -1 -1 -1 -1 -1 -1 -1
1001
B
-1 -1 -1 -1 1 1 -1 -1 -1
1010
B
-1 1 1 -1 -1 -1 -1 1 1 -1
1011
B
- 1 - 1 1 1 - 1 1 1 - 1 1 1 - 1
1100
B
- 1 1 1 - 1 1 1 - 1 1 1 - 1 1 1
1101
B
- 1 1 1 - 1 1 1 1 1 1 1 - 1 1 1
1110
B
- 1 1 1 1 1 1 1 - 1 1 1 1 1 1 1
1111
B
- 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1