ELEC 332

In the Lab

Our major goal for this week is to become proficient in using the MSP430 as a circuit component. We will be using the IAR Embedded Workbench that you used in ELEC 220 for programing and debuging. This weeks exercise could use the 220 hardware setup as well, but in the future we will need greater flexibility than it can provide, so we will start by building our own processor module.

Part 1: Assembling the MSP430 Module

The MSP430 circuit board has been fabricated on the T-Tech circuit milling machine in the Design Kitchen. This system provides low cost and fast turn-around, but the resulting boards have a number of significant differences from the commercially fabbed board we assembled last week. Before you begin assembly, read the instructions on Soldering Milled Boards.


Examine the blank board:

 Here is a top view of the board.

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And the bottom.


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Install wires in all the via holes.

 Since the T-Tech system doesn't produce thru-plated holes, it is necessary to manually connect vias between the top and bottom layers. Here are the locations of all the vias:

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Install the components.

 Here's a map of where they go. Note that C3 is on the bottom of the board.

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This is what it should look like when you are finished:


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The recommended order of assembly is:

  1. Install J1. Remember that it goes on the bottom of the board.
  2. Install the voltage regulator and capacitors. Remember that C2 is polarized. Be sure that the positive terminal is facing to the right. Note: your kit may contain a 22 µF capacitor instead of the 15 µF shown on the circuit diagram.
  3. Verify that the voltage regulator works correctly. Plug your board into the breadboard and turn on the power. The voltage regulator output should be 3.3 V.
  4. Install the remaining components. Remember that D1 is polarized and must be installed in the correct orientation. We will not install the crystal (Y1) at this time.
  5. Install the remaining connectors. The connections to the even-numbered pins of J3 and pins 2 and 4 of J4 must be soldered on the top side of the board, as shown in the photograph.


Inspect your work.

 When you're finished, there should be no empty holes. If there are, you've left out some of the via wires.

Carefully examine both sides of the board under the microscope. Verify that all connections, especially integrated circuit pins, are complete. Check that there are no solder bridges. This is a much greater problem on T-Tech boards than commercial boards because the excess copper is not removed.

Part 2: The Ubiquitous Flashing LED Demo

Our MSP430 module has the same programming/debug connector and LED connection as the MSP-EZ430 target board you used in ELEC 220. This means that we can use the flashing LED demo that comes with the TI kit as a functional test.


Assemble the hardware.

Plug things together so that it looks like this:


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Compile the demo program

as described in Section 5 of the eZ430-F2013 Development Tool User's Guide. One change: replace "MSP430F2013" with "MSP430F2012" in Step 3. Another difference: in Step 4, your choice will be "Texas Instrument USB-IF" rather than "TI USB FET". Copy the FET_examples directory to your own directory and build from there.

Load and run the program.

The debugger is sensitive to the order in which things are connected. Here is a way that works:

  1. With the power off, connect the debugging interface (USB dongle) to the MSP430 module. Be sure that the side of the dongle with the connector is facing away from the center of the board, as shown above. If you have one of the old dongles with the 4-pin connector, plug it into the center 4 holes of the 6-pin connector.
  2. Plug the USB extension cable into the other end of the debugging interface.
  3. Turn on the power.
  4. Start the debugger and proceed as described in the User's Guide.


Try the assembly language version.

 Repeat the above process, but select the "msp430x2xx (asm)" tab rather than "msp430x2xx (C - SpyBiWire)" in Step 2. This will build and run the assembly language version of the flashing light demo. When you start the debugger, you will probably get a message to the effect that "The stack plug-in failed to set a breakpoint on main." You can safely ignore this message.

Part 3: Watch Signals on the Scope

The flashing light demo tells us that our board has been assembled correctly, but isn't very satisfying as a high performance system. Since one of the things we want to do with our microcontroller module is program other high performance chips, we need to be able to flip other bits besides the one connected to the LED. The connector J3 brings five of these bits to the outside world and J4 brings two more. We'll use J4 next week when we look at serial I/O. Right now we're going to play with bits on J3. In particular, we're going to watch the signal on P1.2 on the scope. We will do this by modifying the flashing light demo so that it toggles P1.2 as well as P1.0 (the pin to which the LED is connected). We will then connect P1.2 to the oscilloscope using some of the connector modules.


Set up a working directory.

 Since the demo program that we just ran is shared by all users of the lab computer, it would be inappropriate to modify it. Instead, we will create a new directory in which to do our subsequent work. In the coming weeks, we will be building up a large collection of files (programs, PCB layouts, etc.) which define the modules we are building in lab. You should keep these in a safe place, preferably on a USB flash drive.

Copy the flashing LED demo.

 Copy the flashing light demo code into your new directory. The easiest way to do this is to simply copy the entire "FET_examples" directory structure into your directory. If you like you can remove the "msp430x1xx" and "msp430x4xx" subdirectories.

Modify the demo code.

 Using Open Workspace ... from the File menu, navigate to your new copy of the flashing LED demo. Select either the C or assembly version and make the necessary modifications so that both P1.0 and P1.2 will be toggled.

Add more hardware.

 To view the signal we will need to connect the scope to P1.2. We could do this with the scope probe or clip leads, but the safest, most robust way is to use coax cables. There should already be a BNC to SMB connector module on the breadboard. The module shown below provides a interface between J3 on the processor board and a set of 5 SMB connectors, one for each of the signals on J3. (We only need two of these signals, so only two of the SMB connectors have been installed.)

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Connect this module to the processor module, resulting in the assembly shown below:


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Use a BNC cable and an SMB cable to connect P1.2 to the scope.

Run your program.

 Using the same procedure as in the previous Part, compile, load, and run your program. If all goes well, the light should flash and a low frequency square wave should appear on the scope.

Make the light flash faster.

 The low frequency of the signal makes it easy to see on the LED but hard to observe on the scope. To improve the latter at the expense of the former, modify your program to increase the frequency of the signal to the point where it comfortable to observe on the scope.

Part 4: A/D Conversion

One of the useful features of the MSP430 is that it provides a number of A/D converter inputs. Combined with the ability to produce analog output signals, this allows us to use the MSP430 as a programmable analog signal processing element.

There are a variety of different A/D converter types in the MSP430 family. We have chosen the 2012 (rather than the 2011 or 2013) because it contains a successive approximation converter, which is faster and easier to use than the other choices.


Add still more hardware.

 In order to test the A/D converter, we will need an analog signal source. We could use the function generator, but a more useful source for our current needs is a manually adjustable voltage. The easiest way to get this is with a potentiometer acting as a voltage divider for the Vcc supply voltage. Fortunately, we have a module which does precisely that:

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As circuits go, it's pretty simple:

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Note the 10 kΩ fixed resistor which limits the output voltage range to 0-2.5 V, in order to match the range of the A/D converter.

Make the connections.

 Place the potentiometer module in a convenient location and use a coax jumper to connect its output to P1.4 (the lower-left SMB connector on the connector module).

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Since the potentiometer is connected via a coax cable, it doesn't have to be directly adjacent to the connector module.

Download the A/D converter code.

 Programming the A/D converter is considerably more complicated than programming the digital I/O pins, requiring 31 pages in the User's Guide to describe it vs. 8 for digital I/O. It's even more complicated than that, since the A/D converter interacts with the Basic Clock Module (another 18 pages). Although you should certainly read and understand those pages, a faster way of getting the A/D up and running is to start with some code that already works, and make changes until it works the way you want it to.

Such a program, and another for use in the next Part, are available in the zip file for Exercise 2. Download this file and unzip it into the directory you created in the previous Part. It will create a subdirectory named "lab2".

Build and run the program.

 Open the workspace file lab2.eww in the lab2 directory. Select and build the adc1 project. This program reads the analog input on pin P1.4 and compares it to a fixed threshold (1/2 full scale). If it is greater, it turns on the LED, if less it turns it off. Compile, load, and run the program and verify that it works as intended.

Modify the program.

 Knowing when a physical variable (represented by the voltage on pin P1.4) reaches a particular value is a potentially useful function in a design, so this program might have some utility beyond simply testing the A/D converter. It would have more utility if the threshold value could be changed. Right now our only way of changing it is by editing and recompiling the program. Make the required modifications to set the threshold to a different level (e.g. 1/4 full scale) and verify that your new program functions as intended.

Part 5: PWM

Finally we get to the topic that provided the title for this week's exercise: pulse width modulation, or PWM. We've seen this before in a number of places, for example in 242 in the oven controller. The basic idea is simple: if for some reason you can't provide an adjustable, continuous time analog signal, produce a digital signal whose average value is that of the desired analog signal and put it through a low pass filter.

We will use the same hardware setup as we did in the previous part. However, instead of turning the LED on and off, the signal produced by the potentiometer will be used to control the duty cycle of the signal on P1.2. Since the MSP430 timer is almost as complicated as the A/D converter (24 pages in the User's Guide), we will once again make use of pre-written code.


Select and build the pwm project.

 The code for this part is in the same zip file as that for the previous Part. Simply select the pwm2 project, build, and load.

Verify that it works.

 Set the potentiometer to mid-scale and start the program If all is in order, you should see a square wave of about 50% duty cycle on the scope. Adjust the potentiometer and see how the waveform changes. Characterize this behavior in terms of pulse frequency, relationship of duty cycle to input voltage, etc.

Signal integrity.

 Increase the sweep rate on the scope until you can see the ringing on the rising and falling edges of the PWM output signal. Verify that it's caused by reflections by terminating the cable at the scope using a BNC T-connector and a 50 Ω terminator. Is this ringing significant?

Programming Challenge.

 Rather than modifying the code as in the previous two parts, this time you get to completely (or at least substantially) rewrite it. The details are in the next section, but basically your task is to replace the function of the timer with software. For instructions on how to start a new IAR project, see Starting a new MSP430 project.