HT45F23 datasheet(70/152 Pages) HOLTEK

70 / 152 page

Pulse Width Modulator

This device contains two channels of 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.

Device

Channels

Mode

Pins

Registers

HT45F43

6+2

7+1

PC5

PC6

PWM0

PWM1

PWM Operation

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 BPCTL 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 BPCTL registers, 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 fSYS. This method of dividing the original modulation cycle into a further 2 or 4

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, fSYS, and as

the PWM value is 8-bits wide, the overall PWM cycle frequency is fSYS/256. However, when in the 7+1

mode of operation the PWM modulation frequency will be fSYS/128, while the PWM modulation

frequency for the 6+2 mode of operation will be fSYS/64.

PWM Modulation

PWM Cycle Frequency

PWM Cycle Duty

fSYS/64 for (6+2) bits mode

fSYS/128for (7+1) bits mode

fSYS/256

[PWM]/256

Rev. 1.20

September 15, 2011

HT45F23/HT45F43

8-Bit Flash MCU with Op Amps & Comparators

P W M 0 R e g i s t e r

8 - b i t C o m p a r a t o r 0

P W M 1 R e g i s t e r

8 - b i t C o m p a r a t o r 1

8 - b i t / ( 7 + 1 ) / ( 6 + 2 )

P W M C o u n t e r

P M W 0

P M W 1

PWM Block Diagram

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