ht82j30r Holtek Semiconductor Inc., ht82j30r Datasheet - Page 29

• Manufacturer Part Number: ht82j30r
• Description: Ht82j30r/ht82j30a -- 16 Channel A/d Mcu With Spi Interface
• Manufacturer: Holtek Semiconductor Inc.

Pulse Width Modulator
The device provides a single channel Pulse Width Mod-
ulator function. Useful for such applications such as mo-
tor speed control, the Pulse Width Modulator function
provides an output 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, located in the Data Memory is as-
signed to the Pulse Width Modulator and is known as
the PWM register. It is in this register that the 8-bit value,
which represents the overall duty cycle of one modula-
tion cycle of the output waveform, should be placed. To
increase the PWM modulation frequency, each modula-
tion cycle is modulated into four individual modulation
sub-sections, known as the 6+2 mode. Note that it is
only necessary to write the required modulation value
into the corresponding PWM register as the subdivision
of the waveform into its sub-modulation cycles is imple-
mented automatically within the microcontroller hard-
ware. The PWM clock source is the system clock f
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-
Rev. 1.10
Channels
1
Mode
PWM
6+2
Output
Pins
PD0
Register
Name
6+2 Mode PWM Register
PWM
6+2 PWM Mode
SYS
.
29
quency should be understood. As the PWM clock is the
system clock, f
the overall PWM cycle frequency is f
while the PWM modulation frequency for the 6+2 mode
of operation will be f
6+2 PWM Mode
Each full PWM cycle, as it is controlled by an 8-bit PWM,
PWM0 register, has 256 clock periods. However, in the
6+2 PWM Mode, each PWM cycle is subdivided into
four individual sub-cycles known as modulation cycle
0~modulation cycle 3, denoted as i 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 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 sec-
ond 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.
The following diagram illustrates the waveforms associ-
ated with the 6+2 mode of PWM operation. It is impor-
Modulation cycle i
Parameter
(i=0~3)
6+2 Mode Modulation Cycle Values
SYS
, and as the PWM value is 8-bits wide,
SYS
HT82J30R/HT82J30A
/64.
AC (0~3)
i<AC
i AC
SYS
(Duty Cycle)
March 13, 2008
/256. However,
DC 1
DC
DC
64
64
+