USART Operation: SPI Mode

14.2.5 Serial Clock Control

UCLK is provided by the master on the SPI bus. When MM = 1, BITCLK is provided by the USART baud rate generator on the UCLK pin as shown in Figure 14−8. When MM = 0, the USART clock is provided on the UCLK pin by the master and, the baud rate generator is not used and the SSELx bits are don’t care. The SPI receiver and transmitter operate in parallel and use the same clock source for data transfer.

Figure 14−8. SPI Baud Rate Generator

 

SSEL1 SSEL0 N =

UCLKI

 

 

 

 

 

 

 

 

 

 

 

00

 

BRCLK

 

 

ACLK

 

 

01

 

 

SMCLK

 

 

10

 

 

 

 

 

SMCLK

 

 

11

 

 

 

 

 

 

215

...

28

27

...

20

 

 

 

 

 

 

 

 

 

 

 

UxBR1

 

 

 

UxBR0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8

 

 

 

 

 

8

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

16−Bit Counter

 

 

R

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Q15

............

 

Q0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Compare (0 or 1)

 

 

 

 

 

 

 

 

 

Toggle

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FF

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Modulation Data Shift Register

R

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(LSB first)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

mX

 

 

m7

8 m0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UxMCTL

 

 

 

 

 

 

 

Bit Start

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BITCLK

The 16-bit value of UxBR0+UxBR1 is the division factor of the USART clock source, BRCLK. The maximum baud rate that can be generated in master mode is BRCLK/2. The maximum baud rate that can be generated in slave mode is BRCLK. The modulator in the USART baud rate generator is not used for SPI mode and is recommended to be set to 000h. The UCLK frequency is given by:

Baud rate = BRCLKUxBR with UxBR= [UxBR1, UxBR0]

USART Peripheral Interface, SPI Mode

14-9

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Texas Instruments MSP430x1xx manual Serial Clock Control, 8. SPI Baud Rate Generator
Page 299 Page 301

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.
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