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Lab #8 - Sinclair Community College

1. Page 2 Revised 9 7 2014 above I told you that 5B is the value to show a 2 What is the value to show a 0 to show a1 and so on Next set up a look up table containing these values Your program should read the value on the DIP switches and then find the corresponding entry in the look up table This part of the program is similar to what you did in LabO5LookUpTable Show me your working program 4 Counting on a Seven Segment Display 1 Create a CodeWarrior project named Lab08SevenSegmentCounter choosing HCS12 Serial Monitor on the first page of the New Project Wizard Using the look up table that you created for the previous program write a program that counts up from 0 to F and displays the count on a seven segment display It should count slowly enough that you can read each digit After reaching F the counter should recycle to 0 and start over again 3 Show me your working program 5 Using the HCS12 s Phase Locked Loop to Adjust Clock Speed You ve previously learned that the HCS12 s bus clock normally runs at a frequency of 24 MHz But as you learned in class the clock frequency is programmable using a feature on the chip called a phase locked loop Below you will re program the phase locked loop to cause the bus clock to run faster or slower than normal 1 First let s verify that the normal bus clock frequency really is 24 MHz We ll do this by combining some calculations with an oscilloscope mea
2. frequency must be EET 2261 Lab 8 Page 4 Revised 9 7 2014 increased to 24 MHz To see that this is true we must free the system from CodeWarrior s control and run our program again Here s how to do it Les Add the following two lines to the end of your program but before the END directive These lines define something called a reset vector which we ll discuss next week Put simply these lines tell the chip the starting address of the program that it should run when the user presses the RESET button on the Dragon12 board ORG SFFFE Set up Reset vector DC W Entry Run the program The oscilloscope should display the same period and frequency as it did earlier telling us that the system s bus clock frequency is still 24 MHz Press CodeWarrior s Halt button to stop the program The oscilloscope will display a flat line since you ve stopped the program To free the Dragon12 from CodeWarrior s control locate the two DIP switches near the Dragon12 s lower right corner Notice the word LOAD under the leftmost switch and the word RUN above it Up to now we ve always had this switch in the LOAD position which is where it needs to be to communicate with CodeWarrior Move the leftmost switch to the RUN position but leave the other switch alone By doing this you re telling the system to operate by itself without CodeWarrior s control Press the Dragon12 s RESET button When you do this CodeWarrior
3. 14 As you learned in class we must do something like this e Show a 2 on the leftmost display for an instant Then show a 0 on the second display for an instant e Then show a 1 on the third display for an instant e Then show a 4 on the rightmost display for an instant e Then repeat starting again with the leftmost digit If we move from one display to the next one quickly enough all four displays will appear to be lit up at the same time Following this strategy modify your program so that it shows 2014 on the seven segment displays To control how quickly you move from digit to digit use your delay subroutine from previous programs but adjust the delay time to about 1 millisecond Show me your working program 3 A Look Up Table for the Seven Segment Display 1 Create a CodeWarrior project named Lab08SevenSegmentLookUpTable choosing HCS12 Serial Monitor on the first page of the New Project Wizard Write a program that reads the value of the rightmost four DIP switches on the Dragon12 board and then uses a look up table to show this hex value which will be between 0 and F on a seven segment display For example if the rightmost four DIP switch settings are ON OFF ON OFF which is 1010 then the seven segment display should show an A Hints First you ll have to figure out which value to send to the seven segment display to show each of the hex digits between 0 and F For example in the first program EET 2261 Lab 8
4. Frequency Therefore what is the bus clock frequency Your answer to the previous question should be one half of the last value you calculated on the previous page Call me over to check your work By changing the values of SYNR and REFDV we can get many different clock frequencies In the table below predict the bus clock frequency and the LED blink frequency for each pair of values for SYNR and REFDV Then re run your program with these different values for SYNR and REFDV and measure the actual LED blink frequency SYNR REFDV Predicted Bus Predicted LED Measured LED Blink Clock Frequency Blink Frequency Frequency 0 0 1 4 2 1 5 1 4 0 9 Call me over to check your work EET 2261 Lab 8 Page 6 Revised 9 7 2014
5. Name EET 2261 Lab 8 Seven Segment Displays and Clock Speeds 1 Using a Single Seven Segment Display The Dragon12 Plus2 board has four common cathode seven segment displays As explained on pages 24 26 of the Dragon12 Plus2 board s User Manual the anodes of the displays are connected to the HCS12 s Port B while each display s cathode is connected to one bit of Port P In particular PTPO is connected to the leftmost digit s cathode PTP1 is connected to the next digit s cathode PTP2 is connected to the next digit s cathode and PTP3 is connected to the rightmost digit s cathode To display a digit on one of the displays we must send the correct pattern of bits for that digit to Port B and then ground the cathode of the desired display by making the correct bit of PTP low For example to display the digit 2 on the leftmost display we send 5B or 01011011 to Port B and we send a LOW to PTPO The code below will do the job ABSENTRY Entry INCLUDE derivative inc ORG 2000 Entry CLI Enable interrupts LDS 54000 Stack LDAA EF STAA DDRB Configure PORTB for output STAA DDRP Configure PTP for output LDAA 5B Pattern to show 2 on seven segment STAA PORTB LDAA 00001110 Ground PTPO for leftmost digit STAA PTP BRA Stop END 1 Create a CodeWarrior project named Lab08SingleDigit choosing HCS12 Serial Monitor on the New Project Wizard s first page 2 Enter the program
6. ckly for your eye to see Use an oscilloscope to measure the period and frequency of the waveform on any of the Port B pins Measured Period Measured Frequency Your measurements should match the predictions that you made above Call me over to check your work Our little program above gives us a way to tell what the bus clock frequency is by measuring the frequency of blinking when we run the program In particular we found that the frequency of blinking is one twelfth the bus clock frequency This one twelfth ratio will always hold true for this program Frequency of blinking when we run test program 1 Bus clock frequency 12 Suppose for example that we run our test program on a chip with a different clock frequency and we find that the LEDs blink at 1 MHz Then what must this chip s bus clock frequency be Suppose we run our test program on another chip and we find that the LEDs blink at 200 kHz Then what must this chip s bus clock frequency be You verified above that our chip s normal bus clock frequency is 24 MHz However this is true only when the chip is being controlled by CodeWarrior Otherwise the normal bus clock frequency would be different In other words the Dragon12 board s crystal oscillator gives a default bus clock frequency different from 24 MHz But to communicate with CodeWarrior using a program called the Serial Monitor which is programmed into the HCS12 s Flash memory the bus clock
7. listed above When you run it you should find that the leftmost seven segment displays shows a 2 while the other displays are dark 3 Modify the program to show a 5 on the rightmost seven segment display while the other displays are dark 4 Show me your working program EET 2261 Lab 8 Page 1 Revised 9 7 2014 2 ae Multiple Seven Segment Displays 6 We can easily modify the previous program to show the same digit on all four seven segment displays Create a CodeWarrior project named Lab08MutipleDigits choosing HCS12 Serial Monitor on the New Project Wizard s first page Copy and paste your code from above into the new project Then modify it to display AAAA on all four seven segment displays Hint Since we re showing the same digit on all four displays this program does not require you to use the multiplexing technique discussed in class You simply need to send out the code for A and then enable all four displays When you run the program you may notice that the displays are dimmer than they were when you were showing a single digit That s because seven segment displays draw a fairly large current and when all four of them are lit up they make a considerable demand on the Dragon board s power supply Show me your working program Although it s easy to show the same digit on all four displays showing different digits on different displays at the same time is trickier Suppose we want to show the number 20
8. surement Assuming the bus clock s frequency of 24 MHz what is the system s cycle time Consider the code listing below If Ports B and J have previously been configured to enable the Dragon12 s LEDs as output devices this code will cause the LEDs to blink on and off very fast In the code listing there s a blank next to each instruction Using the Instruction Set Summary fill in these blanks with the number of cycles for each instruction Then add these numbers to find the number of cycles in the loop Loop COMA STAA PORTB BRA Loop Number of cycles in loop Using your answers from the two previous steps how much time is required to execute the loop once EET 2261 Lab 8 Page 3 Revised 9 7 2014 10 11 Each pass through the loop will either turn the LEDs on or turn them off So a complete ON OFF cycle requires two passes through the loop Therefore how much time is required for a complete ON OFF cycle of the LEDs And therefore what will be the frequency of the LED s blinking Predicted Time Predicted Frequency Create a CodeWarrior project named Lab08ClockSpeed choosing HCS12 Serial Monitor on the first page of the New Project Wizard Write a program that contains in addition to the loop shown above any additional code needed to configure the Dragon12 s ports correctly Run the program and the LEDs on the Dragon12 board should light up dimly They re blinking on and off far too qui
9. will complain that it has lost communication with the target system But the program on the HCS12 will run anyway and the oscilloscope will display a waveform with a new period and frequency Record these values below Measured Period Measured Frequency Therefore what is the chip s bus clock frequency when it s not being controlled by CodeWarrior Call me over to check your work To put the Dragon12 system back under CodeWarrior s control move the DIP switch back to the LOAD position and press the Dragon12 s RESET button You may also have to close CodeWarrior s debugger and re open it Now let s reprogram the bus clock frequency to a new value 1 Create a CodeWarrior project named Lab08PhaseLockedLoop choosing HCS12 Serial Monitor on the first page of the New Project Wizard EET 2261 Lab 8 Page 5 Revised 9 7 2014 Copy and paste your LabO8ClockSpeed program into this new project s main asm file and run it to make sure it works Using what you learned in class about the HCS12 s phase locked loop modify the program so that it gives a bus clock frequency that is one half of the bus clock frequency that you calculated on the previous page Download and run the program In this step and from here onward you should leave the Dragon12 s DIP switches in the LOAD position Use the oscilloscope to measure the period and frequency of the LED s blinking Measured Period Measured

Lab #8 - Sinclair Community College

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