MSP430 Tutorial. BY K.Harish. Department of MME, NIT Trichy

Transcription

1 MSP430 Tutorial BY K.Harish Department of MME, NIT Trichy

2 GETTING STARTED WITH MSP430 Launchpad is a low cost development solution to get started with TI s MSP430 Value Line devices. The Launchpad kit includes a MSP430G2 experimenter board, two MSP430G2xx flash microcontrollers, a mini USB cable and a KHz external crystal. The on-board flash emulation tool allows direct interface to a PC through an USB port for easy programming and debugging. These are the advantages of MSP430 among other microcontrollers. MCU AVR/Atmega128L MSP430/F449 PIC/18LF452 Core architecture 8 bit 16 bit 8 bit Power supply V V V Active current (ma at MHz) Idle current (ua at khz) Pin leakage current (na) No of interrupts Peripherals 10 bit ADC 12 bit ADC 10 bit ADC There are two LEDs (red and green) on the board that are connected to P1.0 and P1.6 I/O pins. Similarly, two push buttons for user input and device reset are also available on the board. Making LED blink program using CCS: Code Composer Studio (CCS) is an integrated development environment (IDE) for developing and debugging embedded applications for TI s various processor families. There are many versions of CCS IDE, but I will be

3 talking about CCS v4, which is a recommended version for MSP430 users. Get CCS installed on your computer by downloading it and following the normal steps for installation. Step 1: Start CCS by double clicking the icon on the desktop or selecting it from the Windows Start menu. When CCS loads, the first thing it asks is to define a workspace a directory that holds all elements (projects, links to projects, possibly source code) used in the development. Browse the directory path where you want it to be and do NOT check the Use this as the default and do not ask again checkbox. Click OK. Select Workspace folder Step 2: If this is the first time you have opened CCS then a Welcome to Code Composer Studio v4 page appears.

4 CCS Welcome screen Empty CCS workbench in C/C++ Perspective

5 Step 3: Next step is to create a new project. A project contains all the files you will need to develop an executable output file (.out) which can be run on the MSP430 hardware. To create a new project click: File -> New -> CCS Project Creating a new CCS project Step 4: The next window that appears selects the platform and configurations. The Project Type should be set to MSP430 and the Debug and Release boxes should be checked in the Configurations box. Click Next.

6 Project type is MSP430 Step 5: The next window is to define inter-project dependencies (if any). There are none now. So select Next. No inter-project dependencies for now

7 Step 6: The next step is to select the CCS project settings. Select the Device Variant using the pull-down list and choose MSP430G2231 (the device of your choice). This will select the appropriate linker command file, runtime support library, set the basic build options for the linker and compiler, and set up the target configuration. Select MSP430G2231 for Device Variant Click Finish and a new project is created. You will now see the C/C++ Projects window contains FlashLED project which is set active. Step 7: At this point, the project does not include any source files. The next step is to add the source files to the project. To add a source file to the project, right-click on FlashLED in the C/C++ Projects window and select: New -> Source File. Name the source file main.c and click Finish.

8 Add a new source file main.c Then an empty window will open for the main.c code. Empty window for main.c Step 8: Next, we will add code to main.c. Type in or copy and paste the following code into the main.c window. This code is for flashing the red LED connected to P1.0. #include <msp430g2231.h> //This varies for every mcu unsigned int i; void main(void) { WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer P1DIR = 0x01; // P1.0 is output P1OUT = 0x00; // LED off while(1) { P1OUT ^=BIT0; // Complement output _delay_cycles(500000); // Delay 50K clock cycles } }

9 Save the main.c file after typing up the code Step 9: Next click the Build button or select Project-> Build Active Project and watch the tools run in the Console window. Check for any errors in the Problems window. Step 10: If the build is successful, you are ready to load the program into the target MSP430 device. Make sure that the Launchpad board is connected to the PC. Then click the Debug button (green bug). The Debug Perspective view should open, the program is loaded into the MSP430 device automatically, and you should now be at the start of main(). Debug Perspective In debug mode, you can run the application in either a single step mode using Step Into and Step Over function buttons or a free run mode by clicking on the Run button (see the picture below).

10 Debugging menu If you click on the Run button, the MSP430G2231 processor starts executing the program and the LED on board should blink continuously. Step 11: At last, terminate the active debug session using the Terminate All button. This will close the debugger and return CCS to the C/C++ Perspective view. CCS will remove the breakpoints and release the MSP430G2231 processor in the board so that it could execute freely the program without the need of the debugger. The _delay_cycles(500000); statement in the code creates a delay interval of clock cycles. If you want to convert it into time, you need to know the time period or frequency of the clock. MSP430 devices have multiple sources of clock including internally generated clocks (known as internal digitally controlled oscillator, DCO) and external source (using crystal). On power on reset, the default clock source comes from the internal DCO module. The default value of this clock is around 1.0 MHz (the internal oscillator is not very accurate). So, the _delay_cycles(500000); statement should create a delay of approximately 0.5 sec interval.

11 TIMERS in MSP430 There are two 16-bit timers are available in MSP430G2553, excluding watch dog timer. Timer_A0 Timer_A1 Each 16-bit timer starts counts from 0 to 0x0FFFF (0 to 65536) and they operate in four different modes. Stop --- Timer is in halt state or stops the timer. UP --- Timer counts up from zero to value stored in TACCR0 register (other than 0xFFFF) and roll over to zero after it reached the count value. Generally this mode used to produce time delays. Continuous --- it is same as UP mode but here Timer counts up from zero to maximum value 0xFFFFh and rolls over to zero after it reached 0xFFFF. Up/Down --- in this mode time counts up from 0 to TACCR0 register and then counts down back to zero. It is good for generating PWM and driving motors. MSP430 CPU and other system devices use three internal clocks: 1. Master clock, MCLK, is used by the CPU and a few peripherals. 2. Subsystem master clock, SMCLK, is distributed to peripherals. 3. Auxiliary clock, ACLK, is also distributed to peripherals. Typically SMCLK runs at the same frequency as MCLK, both in the megahertz range. ACLK is often derived from a watch crystal and therefore runs at a much lower frequency. Most peripherals can select their clock from either SMCLK or ACLK. For the MSP430 processor, both the MCLK and SMCLK clocks are supplied by an

12 internal digitally controlled oscillator (DCO), which runs at about 1.1 MHz. TA0CTL Timer A0 control register. TASSEL_1 = 01 in bits 9-8, selects timer A 0 source clock as ACLK, 12KHz. MC_1 = 01 in bits 5-4, sets UP count mode, counting up to the value in TA0CCR0 and generating an interrupt if enabled. TASSELx Bits 9-8 Timer_A clock source select 00 TACLK 01 ACLK 10 SMCLK 11 INCLK (INCLK is device-specific) IDx Bits 7-6 Input divider. These bits select the divider for the input clock. 00 /1 01 /2 10 /4 11 /8 MCx Bits 5-4 Mode control. Setting MCx = 00h when Timer_A is not in use conserve

13 power. 00 Stop mode: the timer is halted. 01 Up mode: the timer counts up to TACCR0. 10 Continuous mode: the timer counts up to 0FFFFh. 11 Up/down mode: the timer counts up to TACCR0 then down to 0000h. TACLR Bit 2 Timer_A clear. Setting this bit resets TAR, the clock divider, and the count direction. The TACLR bit is automatically reset and is always read as zero. TAIE Bit 1 Timer_A interrupt enable. This bit enables the TAIFG interrupt request. 0 Interrupt disabled 1 Interrupt enabled TAIFG Bit 0 Timer_A interrupt flag 0 No interrupt pending 1 Interrupt pending

14 ADC in MSP430 ADC in MSP430 is often performed by successive approximation(sa). A successive approximation A/D converter consists of a comparator, a successive approximation register (SAR), output latches, and a D/A converter. The essentials of the process are: 1. A digital counter is driven by a clock, so each tick updates the counter. 2. The counter output determines an output voltage. 3. The analog voltage input is compared with the output voltage. 4. When the input and output voltage match, the counter holds the digital value. Because of the time it takes time for the counter to "find" the proper value, an ADC is generally much slower than the CPU. To prevent receiving stale or erroneous results, after starting an ADC conversion the CPU can poll the ADC to determine when the conversion is complete. The MSP430 also has an inbuilt temperature sensor. The complete list of registers for the ADC is given below and can also be found on the datasheet. I am not going in depth into the registers as it is self- explanatory, just follow the code in the example below and see how the ADC is implemented. At the start of a conversion cycle, the SAR is reset by making the start signal (S) high. The MSB of the SAR is set as soon as the first transition from LOW to HIGH is introduced. The output is given to the D/A converter which produces an analog equivalent of the MSB and is compared with the analog input V in. If comparator output is LOW, D/A output will be greater than V in and the MSB will be cleared

15 by the SAR. If comparator output is HIGH, D/A output will be less than V in and the MSB will be set to the next position by the SAR. According to the comparator output, the SAR will either keep or reset the Q6 bit. This process goes on until all the bits are tried. After Q0 is tried, the SAR makes the conversion complete(cc) signal HIGH to show that the parallel output lines contain valid data. The CC signal in turn enables the latch, and digital data appear at the output of the latch. As the SAR determines each bit, digital data is also available serially.

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19 #include<msp430g2553.h> void tempinit() {ADC10CTL0=SREF_1 + REFON + ADC10ON + ADC10SHT_3; //1.5V ref,ref on,64 clocks for sample ADC10CTL1=INCH_10+ ADC10DIV_3; //temp sensor is at 10 and clock/4} int tempout() {int t=0; delay_cycles(1000); //wait 4 ref to settle ADC10CTL0 = ENC + ADC10SC; //enable conversion and start while(adc10ctl1 & BUSY); //converting.. t=adc10mem; //store value in t ADC10CTL0&=~ENC; //disable adc conv return(int) ((t * 27069L L) >> 16); //convert and pass} void main(void) { volatile int temp; //initialise WDTCTL = WDTPW + WDTHOLD; //stop Watchdog Timer temp=0; tempinit(); //initialise adc while(1) { delay_cycles(500); //wait and set break point temp=tempout(); //read temp delay_cycles(500);}} //wait and set breakpoint

20 REFERENCES: 1. MSp430 user guide and manual.