MSP430™ microcontrollers

MSP430™ microcontrollers (MCUs) from Texas Instruments are 16-bit, RISC-based, mixed-signal processors designed specifically for ultra-low power. MSP430 MCUs have the right mix of analog and digital integrated intelligent peripherals, ease of use, low cost and lowest power consumption for thousands of applications ranging from simple sensor designs to complex electricity meters.

To get a better idea of what the MSP430 MCU is and how you can use it to solve a system design need or application problem, let’s take a look at a typical block diagram for a device. Figure 1 is the device block diagram for the MSP430G2553, one of the MSP430 Value Line devices.

Figure 1

The purpose of the block diagram is to provide a high-level reference of the integration and feature set found in a given device. You can find the block diagram for any MSP430 MCU in the data sheets at www.msp430.com.

The block diagram contains key features of the device that can help you quickly identify if an MSP430 MCU is a fit for a given application need. There are a few features you will need to consider:

Figure 2 is the corresponding pinout also found in each device data sheet for the MSP430G2553. Here you can see exactly how peripheral functions are mapped onto the multiplexed I/Os of the device. Each I/O pin can be configured in software to provide the desired pin function for a given I/O based on its internal connectivity.

Figure 2

Figure 2 also shows the necessary power-supply connections (DVCC, DVSS), programmer/debugging tool connections (SBWTCK, SBWTDIO), and general I/O and peripheral connections (P3.1, TA1.0, CA2, UCB0SDA). When beginning any design with the MSP430 MCU, reviewing the given device’s block diagram and package pinout can provide a great guide to what is possible, as well as any constraints (such as memory size or pinout limitations).

Connecting the MSP430 MCU in any system is, in most cases, very straightforward. The first consideration should be the power-supply requirements. Most MSP430 devices operate at 1.8 V to 3.6 V, so a typical 3-V supply will work great. Connecting the JTAG to support device memory programming and debugging is also important. For MSP430G2xxx devices, there are two possibilities: standard four-wire JTAG or MSP430 MCU-specific Spy-Bi-Wire (SBW, or two-wire JTAG). Both interfaces are acceptable for programming and debugging application code. The main advantage of the four-wire mode is speed. The main advantage of the two-wire SBW mode is reduced pin-connection requirements.

Figure 3 is an example schematic thatshows the baseline connections for the MSP430G2553, as well as some examples of other connections that can be made to the I/Os and integrated peripherals.

Figure 3

Figure 3 shows the connections of the MSP430G2553 in a typical sensor interface application. In this example, the MSP430G2553's integrated ADC10 is used to measure an analog signal via a thermistor that changes resistance as temperature increases or decreases, and also interfaces using an I2C bus from the USCI module to an external humidity sensor. In addition, a 32.768-kHz watch crystal keeps accurate timing; two switches, along with one PWM-controlled LED, provide a simple user interface. To save power from the 3-V coin cell battery, when not in use the humidity sensor and thermistor ladder can be powered off using a general-purpose I/O (P2.5) and the internal voltage reference (VREF+), respectively.

Now that we've covered the basics and how to understand the capabilities of a given MSP430 device, let’s look more closely at the documentation and how to use it most effectively. MSP430 device documentation can be broken up into three main categories:

You can find these documents, as well as additional reference material such as application notes, example code and development tool documentation, by navigating to the device-specific product folder (e.g., MSP430G2553 product folder). Here, you can find the latest information as well as links to all pertinent documentation and software to aid your design efforts.

Arguably, the most valuable document is the device-specific data sheet. We have already looked at two core aspects (pinout and block diagram), but let’s dive a bit deeper into the information provided. The front page of the data sheet is designed to highlight all of the key aspects of the device organized into bulleted lists (Figure 4). It is comprehensive, showing typical power consumption, clock system capabilities, peripheral mix and package options.

Figure 4

This information is a great start, but is targeted as more of a marketing message than a reference. Going beyond the first page is critical to fully assess the given device’s capabilities and its limitations. Looking beyond the first page begins to yield the information needed to really design a system with the MSP430 MCU. This begins with the available options for the device and variants. For example, there are 40 device and orderable part number variants for the MSP430G2553 device. These variants provide different mixes of flash or RAM, peripherals available, number of I/Os supported, and package options such as DIP or surface-mount options.

While all information in a data sheet should be considered important, we recommend focusing on these areas when reviewing a data sheet for a specific MSP430 MCU:

Figure 5

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Figure 11

Now that we have reviewed the MSP430 device documentation and where to find information about what a device can do, let’s walk through the process of actually selecting the part that best suits a given design need.

Let’s start by answering the questions below:

Numerous devices available in the MSP430 family portfolio can meet the given system requirements uncovered in these questions. We've listed a few in Table 1, with their own unique feature sets. A key driver in listing these specific parts is their ease of use. They are available in DIP packages and are supported by a flexible and scalable development tool that can accelerate prototyping of a given application.

Table 1. Three MSP430 devices with typical characteristics.

Each of the devices can be used with the MSP430 MCU LaunchPad to provide an easy, intuitive and out-of-the-box development experience (Figure 12).

Figure 12

Solving any design challenge begins by understanding the problem and any constraints that the system may have. Once you have established a clear picture of the problem you need to solve, finding the ideal way to solve that problem – using an MCU – can be straightforward if you understand the capabilities that MCUs offer. Being able to navigate the MSP430 family, its feature set, and the available devices and development tools are keys to success in meeting such a system design challenge.

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This work is licensed by Zack Albus under a Creative Commons Attribution License (CC-BY 3.0), and is an Open Educational Resource.

Last edited by Gene Frantz on Mar 7, 2013 1:45 pm -0600.