Polled LVI Operation | Freescale Semiconductor MC68HC908MR32

Low-Voltage Inhibit (LVI)

Once an LVI reset occurs, the MCU remains in reset until VDD rises above a voltage, VLVRX + VLVHX. VDD must be above VLVRX + VLVHX for only one CPU cycle to bring the MCU out of reset. See

14.3.2.6Low-Voltage Inhibit (LVI) Reset. The output of the comparator controls the state of the LVIOUT flag in the LVI status register (LVISCR).

An LVI reset also drives the RST pin low to provide low-voltage protection to external peripheral devices. See 19.5 DC Electrical Characteristics.

Addr.	Register Name		Bit 7	6	5	4	3	2	1	Bit 0

	LVI Status and Control Register	Read:	LVIOUT	0	TRPSEL	0	0	0	0	0


$FE0F	(LVISCR)	Write:	R	R		R	R	R	R	R
	See page 99.
	See page 99.	Reset:	0	0	0	0	0	0	0	0
				= Reserved
			R	= Reserved

Figure 9-2. LVI I/O Register Summary

9.3.1 Polled LVI Operation

In applications that can operate at VDD levels below VLVRX, software can monitor VDD by polling the LVIOUT bit. In the configuration register, the LVIPWR bit must be 1 to enable the LVI module, and the LVIRST bit must be 0 to disable LVI resets. See Chapter 5 Configuration Register (CONFIG). TRPSEL in the LVISCR selects VLVRX.

9.3.2 Forced Reset Operation

In applications that require VDD to remain above VLVRX, enabling LVI resets allows the LVI module to

reset the MCU when VDD falls to the VLVRX level and remains at or below that level for nine or more consecutive CPU cycles. In the CONFIG register, the LVIPWR and LVIRST bits must be 1s to enable the

LVI module and to enable LVI resets. TRPSEL in the LVISCR selects VLVRX.

9.3.3 False Reset Protection

The VDD pin level is digitally filtered to reduce false resets due to power supply noise. In order for the LVI

module to reset the MCU, VDD must remain at or below VLVRX for nine or more consecutive CPU cycles. VDD must be above VLVRX + VLVHX for only one CPU cycle to bring the MCU out of reset. TRPSEL in the LVISCR selects VLVRX + VLVHX.

9.3.4 LVI Trip Selection

The TRPSEL bit allows the user to chose between 5 percent and 10 percent tolerance when monitoring the supply voltage. The 10 percent option is enabled out of reset. Writing a 1 to TRPSEL will enable 5 percent option.

NOTE

The microcontroller is guaranteed to operate at a minimum supply voltage.

The trip point (VLVR1 or VLVR2) may be lower than this. See 19.5 DC

Electrical Characteristics.

MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1

98	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.

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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, MC68HC908MR16 Polled LVI Operation, Forced Reset Operation

Models: MC68HC908MR16 MC68HC908MR32