MC68HC05T16 Datasheet, PDF (67/128 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit

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PULSE WIDTH MODULATOR
The MC68HC05T16 has 10 PWM channels, with output pins shared with port E and port F pins.
Nine 7-bit channels are driven by the Timer clock, the other single 14-bit channel is driven by the
CPU clock. All PWM outputs are +12V open-drain type; therefore a pull-up resistor is required at
each PWM pin.
8.1
7-Bit PWM Channels
The 7-bit PWM system works in conjunction with the 16-bit free running timer to implement nine
channels of conversion. A PWM register is allocated for each PWM channel. Channels PWM0 to
PWM8, located at $2C to $34 respectively. Each 7-bit PWM data register has the same bit
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structure as shown below:
PWM0
:
PWM8
Address bit 7
$2C
$34
bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
0PWM6 0PWM5 0PWM4 0PWM3 0PWM2 0PWM1 0PWM0
:
8PWM6 8PWM5 8PWM4 8PWM3 8PWM2 8PWM1 8PWM0
State
on reset
0000 0000
0000 0000
The driving clock for the 7-bit PWM channels is the 16-bit free-running timer clock divide by 2. For
a 2.1MHz CPU clock, PWM clock = 2.1MHz/4/2 = 262500Hz. The PWM pulse period is
128 x 1/262500Hz = 487.62µs, i.e. a repetition frequency of 2050.8Hz. The duty cycle is
proportional to the value in the corresponding PWM data register. A value of $00 loaded into these
registers results in a continuously low output on the corresponding PWM output pin with external
pull-up resistor connected. A value of $40 results in a 50% duty cycle output. The maximum value
of $7F results in a 127/128 duty cycle output.
Changes to the value in the PWM registers will only become effective after the end of the current
PWM cycle. This prevents erroneous PWM output during value update.
In Stop mode, the oscillator is stopped asynchronously with PWM operation. As a consequence,
the PWM output will remain at the state at the moment when the oscillator is stopped. The PWM
output might be at its high or low state at that moment, and it remains at that state until Stop mode
MC68HC05T16
PULSE WIDTH MODULATOR
TPG
MOTOROLA
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