The MSP430 is a mixed-signal microcontroller family from Texas Instruments. Built around a 16-bit CPU, the MSP430 is designed for low cost and, specifically, low power consumption embedded applications.

The MSP430 can be used for low powered embedded devices. The current drawn in idle mode can be less than 1 µA. The top CPU speed is 25 MHz. It can be throttled back for lower power consumption. The MSP430 also uses six different low-power modes, which can disable unneeded clocks and CPU. Additionally, the MSP430 is capable of wake-up times below 1 microsecond, allowing the microcontroller to stay in sleep mode longer, minimizing its average current consumption. The device comes in a variety of configurations featuring the usual peripherals: internal oscillator, timer including PWM, watchdog, USART, SPI, I²C, 10/12/14/16/24-bit ADCs, and brownout reset circuitry. Some less usual peripheral options include comparators (that can be used with the timers to do simple ADC), on-chip op-amps for signal conditioning, 12-bit DAC, LCD driver, hardware multiplier, USB, and DMA for ADC results. Apart from some older EPROM (MSP430E3xx) and high volume mask ROM (MSP430Cxxx) versions, all of the devices are in-system programmable via JTAG (full four-wire or Spy-Bi-Wire) or a built in bootstrap loader (BSL) using UART such as RS232, or USB on devices with USB support.

There are, however, limitations that preclude its use in more complex embedded systems. The MSP430 does not have an external memory bus, so it is limited to on-chip memory (up to 512 KB flash memory and 66 KB RAM) which may be too small for applications that require large buffers or data tables. Also, although it has a DMA controller, it is very difficult to use it to move data off the chip due to a lack of a DMA output strobe.

There are six general generations of MSP430 processors. In order of development, they were the ‘3xx generation, the ‘1xx generation, the ‘4xx generation, the ‘2xx generation, the ‘5xx generation, and the ‘6xx generation. The digit after the generation identifies the model (generally higher model numbers are larger and more capable), the third digit identifies the amount of memory on board, and the fourth, if present, identifies a minor model variant. The most common variation is a different on-chip analog-to-digital converter.

The 3xx and 1xx generations were limited to a 16-bit address space. In the later generations this was expanded to include ‘430X’ instructions that allow a 20-bit address space. As happened with other processor architectures (e.g. the processor of the PDP-11), extending the addressing range beyond the 16-bit word size introduced some peculiarities and inefficiencies for programs larger than 64 kBytes.

In the following list, it helps to think of the typical 200 mA·Hr capacity of a CR2032 lithium coin cell as 200,000 μA·Hr, or 22.8 μA·year. Thus, considering only the CPU draw, such a battery could supply a 0.7 μA current draw for 32 years. (In reality, battery self-discharge would reduce this number.)

The significance of the ‘RAM retention’ vs the ‘real-time clock mode’ is that in real time clock mode the CPU can go to sleep with a clock running which will wake it up at a specific future time. In RAM retention mode, some external signal is required to wake it, e.g. I/O pin signal or SPI slave receive interrupt.


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