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CHAPTER 14 PWM TIMER
14.1 Overview of PWM Timer
The PWM timer can efficiently output accurate PWM waveforms.
The MB91F109 contains four channels of PWM timer.
Each channel consists of a 16-bit counter, a 16-bit data register with a cycle setting
buffer, a 16-bit compare register with a duty cycle setting buffer, and a pin controller.
■
Characteristics of PWM Timer
• The count clock for the 16-bit counter can be selected from the following four types:
• Internal clock:
φ
,
φ
/4,
φ
/16,
φ
/64
• The counter value can be initialized to "FFFF
H
" by resetting or a counter borrow.
• PWM output is enabled through each channel.
•Registers
• Cycle setting register: Data register for reloading containing a buffer
• Duty cycle setting register: Compare register containing a buffer
• Transfer from the buffer is triggered by a counter borrow.
•Pin control
• The pin is set to "1" when duty cycles match. (Priority)
• The pin is reset to "0" when a counter borrow occurs.
• Because the constant output level mode is supported, output can be maintained at a low
or high level.
• Polarity specification is enabled.
• The following events can be selected as causes for interrupt requests:
• PWM timer activation
• Occurrence of counter borrow (cycle matching)
• Occurrence of duty cycle matching
• Occurrence of counter borrow (cycle matching) or duty cycle matching
An interrupt request thus caused can start DMA transfer.
• Software or another interval timer can activate multiple channels simultaneously. Restarting
during operation is also enabled.