USART Operation: SPI Mode

14.2.3 Slave Mode

Figure 14−3. USART Slave and External Master

 

MASTER

SIMO

SIMO

SLAVE

 

 

 

 

 

 

 

SPI Receive Buffer

 

Transmit Buffer UxTXBUF

Receive Buffer UxRXBUF

 

 

Px.x

STE

 

 

 

 

 

STE

SS

 

 

 

 

 

Port.x

 

 

 

 

 

 

 

 

 

 

 

SOMI

SOMI

 

Receive Shift Register

Data Shift Register DSR

Transmit Shift Register

MSB

LSB

 

MSB

LSB

MSB

LSB

COMMON SPI

SCLK

UCLK

MSP430 USART

 

 

 

 

Figure 14−3 shows the USART as a slave in both 3-pin and 4-pin configurations. UCLK is used as the input for the SPI clock and must be supplied by the external master. The data-transfer rate is determined by this clock and not by the internal baud rate generator. Data written to UxTXBUF and moved to the TX shift register before the start of UCLK is transmitted on SOMI. Data on SIMO is shifted into the receive shift register on the opposite edge of UCLK and moved to UxRXBUF when the set number of bits are received. When data is moved from the RX shift register to UxRXBUF, the URXIFGx interrupt flag is set, indicating that data has been received. The overrun error bit, OE, is set when the previously received data is not read from UxRXBUF before new data is moved to UxRXBUF.

Four-Pin SPI Slave Mode

In 4-pin slave mode, STE is used by the slave to enable the transmit and receive operations and is provided by the SPI master. When STE is low, the slave operates normally. When STE is high:

-Any receive operation in progress on SIMO is halted

-SOMI is set to the input direction

A high STE signal does not reset the USART module. The STE input signal is not used in 3-pin slave mode.

14-6USART Peripheral Interface, SPI Mode

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Texas Instruments MSP430x1xx manual Four-Pin SPI Slave Mode
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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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