PWM Generators, Prescaler | Freescale Semiconductor MC68HC908MR32

Pulse-Width Modulator for Motor Control (PWMMC)

12.3.2 Prescaler

To permit lower PWM frequencies, a prescaler is provided which will divide the PWM clock frequency by 1, 2, 4, or 8. Table 12-1shows how setting the prescaler bits in PWM control register 2 affects the PWM clock frequency. This prescaler is buffered and will not be used by the PWM generator until the LDOK bit is set and a new PWM reload cycle begins.

	Table 12-1. PWM Prescaler

	Prescaler Bits	PWM Clock Frequency
	PRSC1 and PRSC0	PWM Clock Frequency
	PRSC1 and PRSC0

	00	fOP
	01	fOP/2
	10	fOP/4
	11	fOP/8

12.4 PWM Generators

Pulse-width modulator (PWM) generators are discussed in this subsection.

12.4.1 Load Operation

To help avoid erroneous pulse widths and PWM periods, the modulus, prescaler, and PWM value registers are buffered. New PWM values, counter modulus values, and prescalers can be loaded from their buffers into the PWM module every one, two, four, or eight PWM cycles. LDFQ1 and LDFQ0 in PWM control register 2 are used to control this reload frequency, as shown in Table 12-2. When a reload cycle arrives, regardless of whether an actual reload occurs (as determined by the LDOK bit), the PWM reload flag bit in PWM control register 1 will be set. If the PWMINT bit in PWM control register 1 is set, a CPU interrupt request will be generated when PWMF is set. Software can use this interrupt to calculate new PWM parameters in real time for the PWM module.

Table 12-2. PWM Reload Frequency

	Reload Frequency Bits	PWM Reload Frequency
	LDFQ1 and LDFQ0	PWM Reload Frequency
	LDFQ1 and LDFQ0

	00	Every PWM cycle

	01	Every 2 PWM cycles

	10	Every 4 PWM cycles

	11	Every 8 PWM cycles

MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1

122	Freescale Semiconductor

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.

Freescale Semiconductor MC68HC908MR32 manual PWM Generators, Load Operation, PWM Prescaler

Models: MC68HC908MR16 MC68HC908MR32