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CHAPTER 13 PWM UNIT
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User’s Manual U14359EJ4V0UM
(2) PWM buffer registers 0, 1 (PWMB0, PWMB1)
The PWMBn register is a 12-bit buffer register that is used to set control data for the active signal width of
PWMn output. Bits 15 to 12 are fixed to zero. Even if 1 is written in these bits, it is ignored. It is possible to
directly read the values of bits 11 to 8 as written irrespective of the bit length setting made by the PWMCn
register.
The contents in PWMBn registers are transferred to compare registers (CMPn) at the timing of the
generation of an overflow from the PWMn output control counter (TMPn).
The PWM buffer registers can be read or written in 16-bit units.
Remark
n = 0, 1
15
0
14
0
13
0
12
0
11
PWM
B11
10
PWM
B10
9
PWM
B9
8
PWM
B8
7
PWM
B7
6
PWM
B6
5
PWM
B5
4
PWM
B4
3
PWM
B3
2
PWM
B2
1
PWM
B1
0
PWM
B0
PWMB0
15
0
14
0
13
0
12
0
11
PWM
B11
10
PWM
B10
9
PWM
B9
8
PWM
B8
7
PWM
B7
6
PWM
B6
5
PWM
B5
4
PWM
B4
3
PWM
B3
2
PWM
B2
1
PWM
B1
0
PWM
B0
PWMB1
Address
FFFFFC02H
After reset
0000H
Address
FFFFFC12H
After reset
0000H
13.4 Operation
13.4.1 Basic operations
When a PWMn pulse is output, the required data is first set to the PWMCn and PWMBn registers, then the
PWMCn register’s PWMEn bit is set (1). This clears (0) the counter (TMPn) and, when the first overflow occurs, the
active level is set for PWMn output and the data is transferred from the PWMBn register to the compare register
(CMPn). Afterward, PWMn output goes inactive when a match occurs between the TMPn and CMPn register values.
When this is repeated, a PWMn signal whose active level is specified by the ALVn bit in the PWMCn register is
output from the PWMn pin.
When the PWMCn register’s PWMEn bit is cleared (0), PWMn output is stopped immediately and is set to the
inactive level for the ALVn level specified by the PWMCn register.
If, during PWMn signal output, the values of the PWPn2 to PWPn0 bits, PRMn1 and PRMn0 bits, or ALVn bit are
changed, the cycle width and pulse width of the PWMn signal are not guaranteed within the cycle where the changes
were made.
Remark
n = 0, 1