8.2.3Initiating DMA Transfers

Each DMA channel is independently configured for its trigger source with the DMAxTSELx bits as described in Table 8−2.The DMAxTSELx bits should be modified only when the DMACTLx DMAEN bit is 0. Otherwise, unpredictable DMA triggers may occur.

When selecting the trigger, the trigger must not have already occurred, or the transfer will not take place. For example, if the TACCR2 CCIFG bit is selected as a trigger, and it is already set, no transfer will occur until the next time the TACCR2 CCIFG bit is set.

Edge-Sensitive Triggers

When DMALEVEL = 0, edge-sensitive triggers are used and the rising edge of the trigger signal initiates the transfer. In single-transfer mode, each transfer requires its own trigger. When using block or burst-block modes, only one trigger is required to initiate the block or burst-block transfer.

Level-Sensitive Triggers

When DMALEVEL = 1, level-sensitive triggers are used. For proper operation, level-sensitive triggers can only be used when external trigger DMAE0 is selected as the trigger. DMA transfers are triggered as long as the trigger signal is high and the DMAEN bit remains set.

The trigger signal must remain high for a block or burst-block transfer to complete. If the trigger signal goes low during a block or burst-block transfer, the DMA controller is held in its current state until the trigger goes back high or until the DMA registers are modified by software. If the DMA registers are not modified by software, when the trigger signal goes high again, the transfer resumes from where it was when the trigger signal went low.

When DMALEVEL = 1, transfer modes selected when DMADTx = {0, 1, 2, 3} are recommended because the DMAEN bit is automatically reset after the configured transfer.

Halting Executing Instructions for DMA Transfers

The DMAONFETCH bit controls when the CPU is halted for a DMA transfer. When DMAONFETCH = 0, the CPU is halted immediately and the transfer begins when a trigger is received. When DMAONFETCH = 1, the CPU finishes the currently executing instruction before the DMA controller halts the CPU and the transfer begins.

Note: DMAONFETCH Must Be Used When The DMA Writes To Flash

If the DMA controller is used to write to flash memory, the DMAONFETCH bit must be set. Otherwise, unpredictable operation can result.

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Texas Instruments MSP430x1xx manual Initiating DMA Transfers, Edge-Sensitive Triggers, Level-Sensitive Triggers
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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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