BS2824 Holtek Semiconductor Inc., BS2824 Datasheet - Page 60

• Manufacturer Part Number: BS2824
• Description: Touch Key Mcu
• Manufacturer: Holtek Semiconductor Inc.

BS2824/BS2854/BS2868
Touch Key MCU
Pulse Width Modulator
Rev. 1.00
PWM Operation
Every device includes an 8-bit PWM function. Useful for such applications such as motor speed
control, the PWM function provides outputs with a fixed frequency but with a duty cycle that can be
varied by setting particular values into the corresponding PWM register.
A single register, known as PWMn and located in the Data Memory is assigned to each Pulse Width
Modulator channel. It is here that the 8-bit value, which represents the overall duty cycle of one
modulation cycle of the output waveform, should be placed. To increase the PWM modulation
frequency, each modulation cycle is subdivided into two or four individual modulation subsections,
known as the 7+1 mode or 6+2 mode respectively. The required mode and the on/off control for each
PWM channel is selected using the CTRL0 register. Note that when using the PWM, it is only
necessary to write the required value into the PWMn register and select the required mode setup and
on/off control using the CTRL0 register, the subdivision of the waveform into its sub-modulation
cycles is implemented automatically within the microcontroller hardware. The PWM clock source is
the system clock f
sub-cycles enable the generation of higher PWM frequencies which allow a wider range of
applications to be served. The difference between what is known as the PWM cycle frequency and
the PWM modulation frequency should be understood. As the PWM clock is the system clock, f
and as the PWM value is 8-bits wide, the overall PWM cycle frequency is f
in the 7+1 mode of operation the PWM modulation frequency will be f
modulation frequency for the 6+2 mode of operation will be f
f
f
SYS
SYS
SYS
/64 for (6+2) bits mode
/128for (7+1) bits mode
. This method of dividing the original modulation cycle into a further 2 or 4
Modulation
BS2868
PWM
Device
Channels
PWM Block Diagram
60
2
PWM Cycle
Frequency
f
SYS
Mode
/256
6+2
7+1
PWM Cycle
[PWM]/256
Registers
SYS
PWM0
PWM1
Duty
/64.
SYS
SYS
/128, while the PWM
/256. However, when
January 27, 2010
SYS
,