Basic Clock Module Operation

4.2.2LFXT1 Oscillator

The LFXT1 oscillator supports ultralow-current consumption using a 32,768-Hz watch crystal in LF mode (XTS = 0). A watch crystal connects to XIN and XOUT without any other external components. Internal 12-pF load capacitors are provided for LFXT1 in LF mode. The capacitors add serially, providing a match for standard 32,768-Hz crystals requiring a 6-pF load. Additional capacitors can be added if necessary.

The LFXT1 oscillator also supports high-speed crystals or resonators when in HF mode (XTS = 1). The high-speed crystal or resonator connects to XIN and XOUT and requires external capacitors on both terminals. These capacitors should be sized according to the crystal or resonator specifications.

LFXT1 may be used with an external clock signal on the XIN pin in either LF or HF mode. When used with an external signal, the external frequency must meet the datasheet parameters for the chosen mode.

Software can disable LFXT1 by setting OSCOFF, if this signal does not source SMCLK or MCLK, as shown in Figure 4−2.

Figure 4−2. Off Signals for the LFXT1 Oscillator

XTS

OSCOFF

CPUOFF SELM0 SELM1

XT2

SCG1

SELS

LFoff

XT1off

XT2 is an Internal Signal

XT2 = 0: MSP430x11xx, MSP430x12xx devices

XT2 = 1: MSP430x13x, MSP430x14x

MSP430x15x, and MSP430x16x devices

Note: LFXT1 Oscillator Characteristics

Low-frequency crystals often require hundreds of milliseconds to start up, depending on the crystal.

Ultralow-power oscillators such as the LFXT1 in LF mode should be guarded from noise coupling from other sources. The crystal should be placed as close as possible to the MSP430 with the crystal housing grounded and the crystal traces guarded with ground traces.

The LFXT1 oscillator in LF mode requires a 5.1-Mresistor from XOUT to VSS when VCC < 2.5 V.

Basic Clock Module

4-5

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Texas Instruments MSP430x1xx manual 2. Off Signals for the LFXT1 Oscillator

MSP430x1xx specifications

The Texas Instruments MSP430x1xx series is a family of ultra-low-power microcontrollers that are highly regarded in the embedded systems community for their versatility and performance. Designed for applications ranging from portable instrumentation to low-power industrial devices, the MSP430x1xx combines flexibility and efficiency with advanced features tailored for energy-sensitive applications.

One of the standout characteristics of the MSP430x1xx is its ultra-low-power operation. This series offers several low-power modes that can significantly extend battery life in portable devices. The microcontroller can be in active mode, low-power mode, or even in a deep sleep state, allowing developers to optimize power consumption based on the application's requirements. In fact, some configurations can operate at just a few microamps, making it ideal for battery-operated devices.

Another key feature is the 16-bit RISC architecture that provides powerful processing capabilities while maintaining a low power profile. The MSP430x1xx series supports a maximum clock speed of 16 MHz, allowing for efficient task execution while consuming minimal energy. This architecture ensures that programs run smoothly while the microcontroller remains energy efficient.

The MSP430x1xx is equipped with various integrated peripherals, including analog-to-digital converters (ADCs), timers, and communication interfaces like UART, SPI, and I2C. The inclusion of a powerful ADC enables the microcontroller to handle sensor readings with high accuracy, making it suitable for applications like environmental monitoring and medical devices. The integrated timers provide essential functionality for real-time applications, allowing for event-driven programming and precise timing control.

Memory options in the MSP430x1xx series are also robust, with configurations offering flash memory sizes from 1 KB to 64 KB. This flexibility allows developers to choose the optimal memory size for their specific applications, accommodating a wide range of requirements.

Additionally, the MSP430x1xx microcontrollers are designed with a wide operating voltage range, typically from 1.8V to 3.6V, making them compatible with various power sources and further enhancing their usability in diverse applications.

In summary, the Texas Instruments MSP430x1xx series of microcontrollers is an excellent choice for developers seeking low-power, high-performance solutions for embedded applications. With an efficient architecture, a rich set of peripherals, and flexible memory options, these microcontrollers are positioned to meet the growing demands of modern electronic designs, particularly in battery-powered and energy-sensitive applications.