LAB 2: Power Modes, and ADC

This lab consists of two parts. In the first part, you will get familiar with low power modes in MSP430. In the second part, Analog to Digital Converter of the MSP430 will be used to sample the accelerometer sensor, perform a simple processing and present the outcome.

1 Lab Objectives

Operation of low power modes o Put the MCU in low power mode o Waking from low power mode o Returning from low power mode to the main function

Understand the use and configuration of the ADC Use the Accelerometer to detect the board orientation

Our hope is that you can finish this lab in one session. We might extend this by one week if necessary. In the interest of starting the final project as soon as possible, please try your best to complete the lab in a week.

2 Pre-Lab

Please read chapter 6 section 10 (6.10) of MSP430 textbook and get familiar with low power modes of MSP430. Consult with the lecture slides. Write a code to put the MCU in low power mode and use interrupts to return to the main function (study the low power mode functions in msp430x54x.h). You also need to read Chapter 20 ADC12_A of the MSP430x5xx/MSP430x6xx Family User's Guide prior to the lab to familiarize yourself with the general features of the ADC. Review the Datasheet for the Accelerometer on the board. The codes with all headers and other files are provided. You should understand how to configure the ADC and the principles behind the sampling. You might be asked to modify the ADC code. In order to detect the orientation of the board, use the X-axis and the Y-axis accelerometer inputs. Write a code that uses these two inputs and shows the orientation of board using the two available LEDs on the experimenter board.

2.1 Requirements

Hardware: An MSP430 Flash Emulation Tool (MSP-FET430UIF) and the Experimenter Board

Software: Code Composer Studio v5

3 Lab Procedure

Repeat all steps you learned in Lab0 to create a new project in CCSv5. You might need to add other resources to your projects.

3.1 Power Modes of MSP430

Create a new project for the lab and include the file msp430x54x_UCS_2.c. This code sets different frequencies for MCLK, SCLK and SMCLK. Run it and use the oscilloscope to measure the frequency via the test points for the different clocks. The Experimenter board includes some test points specifically designed for observing various clocks. The test points also provide a ground.

Use the code you wrote for the pre-lab to send the MCU to the low power modes 0, 3, 4. Observe the effect of each mode on the MCU. In the next step, use interrupts to send the MCU to the active mode. You may use the following functions:

__bis_SR_register(LPM3_bits + GIE); // Enter Mode3, enable interrupts __bic_SR_register_on_exit(LPM3_bits); // Exit low power Mode3

3.2 Detecting Board Orientation

The ADC on experimenter board samples two channels that correspond to the X and Y acceleration axes. Normally with no force applied, the output voltage is VCC/2 or approximately 1.5V (also depends on the battery voltage). From that point, the voltage changes depending on the sensitivity of the accelerometer and the acceleration force. This information is specified in the datasheet in mV/g.

In this part of the lab, you will implement an application to show the X and Y acceleration on display of Experimenter board. Download the package Lab2_part2_code.zip. Create a project and run the code. You will see two lines representing the acceleration of the Experimenter Board in X and Y directions. Note that the gravity itself creates a force that will show up as 1g when the board is held sideways.

Assume that the board is held perpendicular to the floor (or desk -- parallel to the gravity force vector). Depending on the exact orientation, you will see the effect of gravity on either or both axes. In order to detect the orientation of the board, you will need to determine the direction of these forces. There are five possible scenarios as shown in the following figures. To detect the board orientation, you must sense the direction in which the forces are exerted. Although the figures show forces only in one direction, it is clear that when the board is not at the right angle, gravity will be observed on both axes (i.e., g.Sin() and g.Cos() ). The tripping point to detect the orientation of board should not be purely 1g. Rather, you should turn on/off LEDs when particular axis passes a certain point (e.g. 0.6g might be a good value). Once you find the direction and tripping points, status of LEDs would show the board orientation. In this part of the lab, you will use LED1 and LED2 to represent five possible scenarios as follows:

Case1: X and Y accelerations are less than threshold LED1 and LED2 blinking

Case2: negative accelerations less than threshold in X-axis LED1 = off, LED2 = off

Case3: positive accelerations greater than threshold in X-axis LED1 = on, LED2 = off

Case4: negative accelerations less than threshold in Y-axis LED1 = off, LED2 = on

Case5: positive accelerations greater than threshold in Y-axis LED1 = on, LED2 = on

Demonstrate the outcome to the TAs.

4 Lab Questions (to be answered in your report)

o What problems did you encounter in this Lab? o What would determine a proper low power mode for the MSP430? o What is actually triggering the conversion of the ADC? o Considering the ADC resolution, how precisely can you measure the X and Y

accelerations? Support your answer with suitable mathematical equations. o How many ADC block does the MSP430F5438A have? How many analog sources can

be connected to one MSP430F5438A and accommodated concurrently?

5 Lab Report

Include the following in your report: Answers to all questions. Create a zip file for codes and email it to the TAs along with the report.

6 Documents

There are many useful documents you will need as reference during the labs, these include: o MSP-EXP430F5438 Experimenter Board User's Guide This document contains all

the information about the Experimenter board you will be using, some of which will be reproduced here. Designated slau263d and available at the following URL: http://focus.ti.com/lit/ug/slau263d/slau263d.pdf

o MSP430F5438 Datasheet This documents contains much on the information about the MSP430 device itself and its specifications. Although you will not have to deal with the details since you are using a prebuilt board, it is useful to familiarize yourself with it. http://focus.ti.com/lit/ds/symlink/msp430f5438.pdf

o MSP430x5xx/MSP430x6xx Family User's Guide A must have description of the MSP430 individual modules. This document describes them in detail including the registers and the module operation. It will answer many of your questions of how to use the modules of the MSP430F5438. http://focus.ti.com/lit/ug/slau208g/slau208g.pdf

o MSP430F5438 Example Code Texas Instruments provides sample code to perform various functions on the MSP430F5438 and similar MSP430 microcontrollers. This is usually a good starting point to do things and covers many of the Modules http://www.ti.com/litv/zip/slac166o

o MSP-EXP439F5438(A) Example Software - This software runs on the Experimenter board and demonstrates the various features such as LCD, Accelerometer, Microphone, etc. http://www.ti.com/litv/zip/slac227f