HT46R46E datasheet(30/73 Pages) HOLTEK

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HT46R46E/C46E/R47E/C47E/R48AE/C48AE/R49E

Rev. 1.20

August 15, 2007

Pulse Width Modulator

Each microcontroller in the Cost-effective A/D Type

MCU series contains either one or two Pulse Width

Modulation, PWM, outputs. Useful for such applications

such as motor speed control, the PWM function pro-

vides 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

PWM

Mode

Output

Pins

Name

HT46R49E

6+2

PD0/

PD1

PWM0/

PWM1

Other

Devices

6+2

PD0

PWM

For devices with one PWM output, a single register, lo-

cated in the Data Memory is assigned to the Pulse Width

Modulator and is known as the PWM register. For de-

vices with two PWM outputs, two registers are provided

and are known as PWM0 and PWM1. It is in these regis-

ters, that the 8-bit value, which represents the overall

duty cycle of one modulation cycle of the output wave-

form, should be placed. To increase the PWM modula-

tion frequency, each modulation cycle is modulated into

four individual modulation sub-sections, known as the

6+2 mode. Note that it is only necessary to write the re-

quired modulation value into the corresponding PWM

sub-modulation cycles is implemented automatically

within the microcontroller hardware. For all devices, the

PWM clock source is the system clock fSYS.

This method of dividing the original modulation cycle

into a further 4 sub-cycles enables the generation of

higher PWM frequencies, which allow a wider range of

applications to be served. As long as the periods of the

generated PWM pulses are less than the time constants

of the load, the PWM output will be suitable as such long

time constant loads will average out the pulses of the

PWM output. The difference between what is known as

the PWM cycle frequency and the PWM modulation fre-

quency 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, while the

PWM modulation frequency for the 6+2 mode of opera-

tion will be fSYS/64.

PWM

Modulation

Frequency

PWM Cycle

Frequency

PWM Cycle

Duty

fSYS/64

fSYS/256

(PWM register

value)/256

6+2 PWM Mode

Each full PWM cycle, as it is controlled by an 8-bit PWM,

PWM0 or PWM1 register, has 256 clock periods. How-

ever, in the 6+2 PWM Mode, each PWM cycle is subdi-

vided into four individual sub-cycles known as

modulation cycle 0~modulation cycle 3, denoted as

²i²

in the table. Each one of these four sub-cycles contains

64 clock cycles. In this mode, a modulation frequency

increase by a factor of four is achieved. The 8-bit PWM,

PWM0 or PWM1 register value, which represents the

overall duty cycle of the PWM waveform, is divided into

two groups. The first group which consists of bit2~bit7 is

denoted here as the DC value. The second group which

consists of bit0~bit1 is known as the AC value. In the

6+2 PWM mode, the duty cycle value of each of the four

modulation sub-cycles is shown in the following table.

Parameter

AC (0~3)

(Duty Cycle)

Modulation cycle i

(i=0~3)

i<AC

DC 1

³AC

6+2 Mode Modulation Cycle Values

The following diagram illustrates the waveforms associ-

ated with the 6+2 mode of PWM operation. It is impor-

tant to note how the single PWM cycle is subdivided into

4 individual modulation cycles, numbered from 0~3 and

how the AC value is related to the PWM value.

PWM Output Control

On all devices, the PWM outputs are pin-shared with

pins PD0 and PD1. To operate as PWM outputs and not

as I/O pins, the correct PWM configuration options must

be selected. A

²0² must also be written to the corre-

sponding bits in the I/O port control register PDC to en-

sure that the required PWM output pin is setup as an

output. After these two initial steps have been carried

out, and of course after the required PWM value has

been written into the PWM register, writing a

²1² to the

corresponding bit in the PD output data register will en-

able the PWM data to appear on the pin. Writing a

²0² to

the corresponding bit in the PD output data register will

disable the PWM output function and force the output

low. In this way, the Port D data output register can be

used as an on/off control for the PWM function. Note

that if the configuration options have selected the PWM

function, but a

²1² has been written to its corresponding

bit in the PDC control register to configure the pin as an

input, then the pin can still function as a normal input

line, with pull-high resistor options.

HT46R46E Datasheet(PDF) 30 Page - Holtek Semiconductor Inc

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