Pulse-Width Modulator for Motor Control (PWMMC)

12.7 Initialization and the PWMEN Bit

For proper operation, all registers should be initialized and the LDOK bit should be set before enabling the PWM via the PWMEN bit. When the PWMEN bit is first set, a reload will occur immediately, setting the PWMF flag and generating an interrupt if PWMINT is set. In addition, in complementary mode, PWM value registers 1, 3, and 5 will be used for the first PWM cycle if current sensing is selected.

NOTE

If the LDOK bit is not set when PWMEN is set after a RESET, the prescaler and PWM values will be 0, but the modulus will be unknown. If the LDOK bit is not set after the PWMEN bit has been cleared then set (without a RESET), the modulus value that was last loaded will be used.

If the dead-time register (DEADTM) is changed after PWMEN or OUTCTL is set, an improper dead-time insertion could occur. However, the dead-time can never be shorter than the specified value.

Because of the equals-comparator architecture of this PWM, the modulus

=0 case is considered illegal. Therefore, the modulus register is not reset, and a modulus value of 0 will result in waveforms inconsistent with the other modulus waveforms. See 12.9.2 PWM Counter Modulo Registers.

When PWMEN is set, the PWM pins change from high impedance to outputs. At this time, assuming no fault condition is present, the PWM pins will drive according to the PWM values, polarity, and dead-time. See the timing diagram in Figure 12-32.

CPU CLOCK

PWMEN

DRIVE ACCORDING TO PWM

VALUE, POLARITY, AND DEAD-TIME

PWM PINS

HI-Z IF OUTCTL = 0

 

 

 

 

 

 

 

 

 

HI-Z IF OUTCTL = 0

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 12-32. PWMEN and PWM Pins

When the PWMEN bit is cleared, this will occur:

•PWM pins will be three-stated unless OUTCTL = 1.

•PWM counter is cleared and will not be clocked.

•Internally, the PWM generator will force its outputs to 0 to avoid glitches when the PWMEN is set again.

When PWMEN is cleared, these features remain active:

•All fault circuitry

•Manual PWM pin control via the PWMOUT register

•Dead-time insertion when PWM pins change via the PWMOUT register

NOTE

The PWMF flag and pending CPU interrupts are NOT cleared when

PWMEN = 0.

MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1

142

Freescale Semiconductor

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Freescale Semiconductor MC68HC908MR32, MC68HC908MR16 manual Initialization and the Pwmen Bit, Pwmen and PWM Pins
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MC68HC908MR16, MC68HC908MR32 specifications

Freescale Semiconductor's MC68HC908MR32 and MC68HC908MR16 microcontrollers are part of the popular HC08 family, designed primarily for embedded applications. These microcontrollers are particularly favored in automotive, industrial, and consumer product sectors due to their reliability and versatility.

One of the standout features of the MC68HC908MR series is its CMOS technology, which enhances performance while minimizing power consumption. This makes these microcontrollers suitable for battery-operated devices. They operate at a maximum clock frequency of 2 MHz and offer a 16-bit architecture, providing a solid balance between processing power and efficiency.

The MC68HC908MR32 variant is equipped with 32KB of flash memory, which allows for the storage of complex programs and extensive data handling. In contrast, the MC68HC908MR16 features 16KB of flash memory, making it ideal for simpler applications. Both microcontrollers also come with 1KB of RAM, enabling efficient data processing and real-time operations.

Another significant characteristic of these microcontrollers is their integrated peripherals. They come with multiple input/output (I/O) pins, which allow for connectivity with various sensors and actuators. The built-in timer systems offer precise timing control for automotive and industrial applications, while the Analog-to-Digital Converter (ADC) provides essential conversion capabilities for various analog signals.

For communication purposes, the MC68HC908MR series includes a serial communication interface, enabling easy integration with other devices and systems. This versatility facilitates the development of complex systems that require interaction with external components.

Security is another crucial aspect of these microcontrollers. They have built-in fail-safe mechanisms to ensure reliable operation under various conditions, making them suitable for critical systems. Additionally, their robust architecture helps to safeguard against potential disruptions or attacks.

In summary, Freescale Semiconductor's MC68HC908MR32 and MC68HC908MR16 microcontrollers are key players in the embedded systems landscape. Their blend of power efficiency, integrated features, and scalability ensures they remain relevant for a wide array of applications, making them a favored choice among engineers and developers looking for dependable solutions in a competitive market.
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