Clock Synthesizer Operation, Mode Description

Freescale Semiconductor, Inc...

Freescale Semiconductor, Inc.

4.2.2.6.2Using the Periodic Timer as a Real-Time Clock. The periodic interrupt timer can be used as a real-time clock interrupt by setting it up to generate an interrupt with a one-second period. Rearranging the periodic timer period equation to solve for the desired count value:

PITR count value	=	(PIT period) (EXTAL frequency)
		(Prescaler value) (22)
PITR count value	=	(1) (32768)
		(512) (22)
PITR count value	=	16 (decimal)

Therefore, when using a 32.768-kHz crystal, the PITR should be loaded with a value of $10 with the prescaler enabled to generate interrupts at a one-second rate.

4.2.2.7SIMULTANEOUS INTERRUPTS BY SOURCES IN THE SIM40. If multiple interrupt sources at the same interrupt level are simultaneously asserted in the SIM40, it will prioritize and service the interrupts in the following order: 1) software watchdog, 2) periodic interrupt timer, and 3) external interrupts.

4.2.3 Clock Synthesizer Operation

The clock synthesizer can operate with either an external crystal or an external oscillator for reference, using the internal phase-locked loop (PLL) and voltage-controlled oscillator (VCO), or an external clock can directly drive the clock signal at the operating frequency. The four modes of clock operation are listed in Table 4-1.

Table 4-1. Clock Operating Modes

Mode	Description	MODCK	VCCSYN
Mode	Description	Reset	Operating
		Value	Value
	External crystal or oscillator used with the on-chip PLL and VCO to
Crystal Mode	generate a system clock and CLKOUT of programmable rates.	5 V	5 V
External Clock	The desired operating frequency is driven into EXTAL resulting in a
Mode without PLL	system clock and CLKOUT of the same frequency, not tightly coupled.	0 V	0 V
	The desired operating frequency is driven into EXTAL, resulting in a
External Clock	system clock and CLKOUT of the same frequency, with a tight skew
Mode with PLL	between input and output signals.	0 V	5 V
	Upon input signal loss for either clock mode using the PLL, operation
	continues at approximately one-half operating speed (affected by the
Limp Mode	value of the X-bit in the SYNCR).	X	5 V

In crystal mode (see Figure 4-4), the clock synthesizer can operate from the on-chip PLL and VCO, using a parallel resonant crystal connected between the EXTAL and XTAL pins, or an external oscillator connected to EXTAL as a reference frequency source. The oscillator circuit is shown in Figure 4-5. A 32.768-kHz watch crystal provides an inexpensive reference, but the reference crystal or external oscillator frequency can be any frequency in the range specified in Section 11 Electrical Characteristics. When

MOTOROLAMC68340 USER’S MANUAL4- 9

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MC68340 specifications

The Motorola MC68340 is a highly integrated microprocessor that was introduced in the early 1990s. It belongs to the 68000 family of microprocessors and is designed to cater to the demands of embedded systems, particularly in telecommunications and networking applications. This chip represents a significant evolution in microprocessor technology by combining a microprocessor core with additional peripherals on a single chip, making it an attractive solution for engineers looking to design compact and efficient systems.

One of the key features of the MC68340 is its 32-bit architecture, which allows for significant processing power and data handling capabilities. This architecture enables the processor to handle larger data sizes and perform more complex calculations compared to its 16-bit predecessors. The MC68340 operates at clock speeds typically ranging from 16 MHz to 25 MHz. Its dual instruction pipeline enhances throughput, allowing for simultaneous instruction fetches and executions, which significantly boosts performance.

A notable characteristic of the MC68340 is the inclusion of integrated peripherals, which help reduce the overall component count in a system. Key integrated components include a memory management unit (MMU), a direct memory access (DMA) controller, and various communication interfaces such as serial ports. The memory management capabilities enhance the processor's ability to manage memory resources efficiently, enabling it to support multitasking environments commonly found in modern computing.

In terms of connectivity, the MC68340 features connections for both synchronous and asynchronous serial communication, making it well-suited for networking tasks. The processor supports a range of bus standards, including address and data buses, which facilitate seamless interaction with peripheral devices.

Another important aspect of the MC68340 is its flexibility. The processor supports multiple operating modes, including multiple CPU configurations and compatibility with the Motorola 68000 family, allowing for easier integration into existing systems.

Moreover, the MC68340 boasts low power consumption compared to many of its contemporaries, making it an excellent choice for battery-operated applications, enhancing its appeal in sectors like telecommunications, industrial control, and automotive systems. Its combination of performance, integration, versatility, and efficiency has secured the MC68340 a reputable position in the annals of embedded systems technology, proving to be a valuable asset for developers and engineers alike.

Motorola MC68340 Clock Synthesizer Operation, Clock Operating Modes, Mode Description, Value

Models: MC68340

Freescale Semiconductor, Inc...

Freescale Semiconductor, Inc.

4.2.3 Clock Synthesizer Operation

Table 4-1. Clock Operating Modes

Mode

Description

MODCK

Operating

Value

MC68340 specifications