USART Operation: UART Mode

13.2.5 USART Transmit Enable

When UTXEx is set, the UART transmitter is enabled. Transmission is initiated by writing data to UxTXBUF. The data is then moved to the transmit shift register on the next BITCLK after the TX shift register is empty, and transmission begins. This process is shown in Figure 13−6.

When the UTXEx bit is reset the transmitter is stopped. Any data moved to UxTXBUF and any active transmission of data currently in the transmit shift register prior to clearing UTXEx will continue until all data transmission is completed.

Figure 13−6. State Diagram of Transmitter Enable

UTXEx = 0

 

No Data Written

Not Completed

 

to Transmit Buffer

 

 

 

 

 

 

 

 

UTXEx = 1

 

 

UTXEx = 1

Idle State

Data Written to

 

 

Transmit Buffer

 

 

Transmit

Transmission

Handle Interrupt

(Transmitter

Disable

Active

Conditions

Enabled)

 

UTXEx = 0

 

 

 

 

 

 

 

 

 

 

 

Character

 

 

UTXEx = 1

 

Transmitted

UTXEx = 0 And Last Buffer Entry Is Transmitted

When the transmitter is enabled (UTXEx = 1), data should not be written to UxTXBUF unless it is ready for new data indicated by UTXIFGx = 1. Violation can result in an erroneous transmission if data in UxTXBUF is modified as it is being moved into the TX shift register.

It is recommended that the transmitter be disabled (UTXEx = 0) only after any active transmission is complete. This is indicated by a set transmitter empty bit (TXEPT = 1). Any data written to UxTXBUF while the transmitter is disabled will be held in the buffer but will not be moved to the transmit shift register or transmitted. Once UTXEx is set, the data in the transmit buffer is immediately loaded into the transmit shift register and character transmission resumes.

13-10USART Peripheral Interface, UART Mode

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Texas Instruments MSP430x1xx manual Usart Transmit Enable, 6. State Diagram of Transmitter Enable
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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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