Timers, Interrupts, and Square Wave Generation. Ryan Krauss. Southern Illinois University Edwardsville. October 24, 2007

Transcription

1 Timers, Interrupts, and Square Wave Generation Ryan Krauss Southern Illinois University Edwardsville October 24, 2007 Timers and Interrupts - Why should we care? Gives us the ability to precisely schedule events Very useful in signal generation (system ID) Also important for digital control (real-time) In order to move from continuous time model to digital model (from s to z), a precise and consistent dt is needed Real-time control in Windows is complicated and expensive Ryan Krauss Timers, Interrupts, and Square Wave Generation 2 / 17

2 Timer8 Module Used to time things Count is incremented once per clock cycle Interrupt can be generated on counter overflow An interrupt service routine (ISR) can be written to do something on each interrupt We will use the ISR to toggle a pin, so that a square wave is generated Overflow period is adjustable, but cannot be greater than (Timer16, Timer24, and Timer32 modules can have larger periods: 2 n 1) The counter clock is specified by the programmer Ryan Krauss Timers, Interrupts, and Square Wave Generation 3 / 17 Square Wave Project Goal The goal of the square wave project is for you to develop a PSoC Designer project that can generate a square wave for any freqeuency between 100 Hz and 10 khz. You will adjust the frequecy by changing the clock settings and the period of the Timer8 module. You will write software that includes a main function and an ISR to generate the square wave. You will demonstrate that your project correctly generates a square wave of the required frequencies by showing a waveform from either a DAQ card or an oscilloscope. Ryan Krauss Timers, Interrupts, and Square Wave Generation 4 / 17

3 Clock Dividers All user modules are controlled by a specified clock SysClk = 24 MHz V C 1 = SysClk N 1, 1 N 1 16 V C 2 = V C 1 N 2, 1 N 2 16 V C 3 = V C 2 N 3, 1 N V C 3 can have other sources besides V C 2 Ryan Krauss Timers, Interrupts, and Square Wave Generation 5 / 17 Timer8 Module Settings Clock? Capture Low TerminalCountOut None CompareOut None Period? CompareValue 1 CompareType Less Than InterruptType Terminal Count ClockSync Sync to SysClk TC PulseWidth Full Clock InvertCapture Normal Ryan Krauss Timers, Interrupts, and Square Wave Generation 6 / 17

4 PSoC Designer Start Up Click on Start New Project Ryan Krauss Timers, Interrupts, and Square Wave Generation 7 / 17 New Project Dialog Give the project a name and save it to a temporary folder Ryan Krauss Timers, Interrupts, and Square Wave Generation 8 / 17

5 Important Initial Choices Make sure to choose the part # CY8C PXI and the C language Ryan Krauss Timers, Interrupts, and Square Wave Generation 9 / 17 Add a Timer8 Module Switch to the User Module Selection View Click on Timers and then Timer8 Double click on Timer8 Switch to Interconnect View Right click on Timer8 module and choose Place Ryan Krauss Timers, Interrupts, and Square Wave Generation 10 / 17

6 Next Steps Adjust the different clock dividers (N 1, N 2, and N 3 ) Set the V C 3 clock source Set the Timer8 Parameters and choose the period Save everything and click Generate Application Ryan Krauss Timers, Interrupts, and Square Wave Generation 11 / 17 Application Editor (Software View) Click on the Application Editor view button Open the main.c file from the tree on the left Write your code Ryan Krauss Timers, Interrupts, and Square Wave Generation 12 / 17

7 Timer8 Code Make sure you have this line before your main function: #pragma i n t e r r u p t h a n d l e r Timer8 1 ISR which tells the compiler that the interrupt is in C. You will need the following lines in your main function before an infinite loop: / ensure i n t e r r u p t i s enabled / TIMER8 1 EnableInt ( ) ; / enable the g l o b a l i n t e r r u p t s / M8C EnableGInt ; / s t a r t the counter! / TIMER8 1 Start ( ) ; Ryan Krauss Timers, Interrupts, and Square Wave Generation 13 / 17 ISR The Timer8 ISR must have the prototype: void Timer8 1 ISR ( void ) { / / your code here } Ryan Krauss Timers, Interrupts, and Square Wave Generation 14 / 17

8 How to toggle a pin? How do you use the ISR to generate a square wave? Exclusive Or (XOR) PRT0DR ˆ= 0x01; ˆ= means XOR You must remember to think in binary for the correct pins Ryan Krauss Timers, Interrupts, and Square Wave Generation 15 / 17 Final Steps Compile C code Assemble to hex Program the part Run your code and look at/save the wave form Ryan Krauss Timers, Interrupts, and Square Wave Generation 16 / 17

9 Final Result 5 4 Votlage Time (sec) N 1 =16, N 2 =10, N 3 =6, period=199. Does this make sense? Ryan Krauss Timers, Interrupts, and Square Wave Generation 17 / 17