Training program: Mechanic - electrotechnician Program name: Digital processing - microprocessors III. class Microcontrollers Elaborated by: Vlastimil Vlček Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/ je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.

Practical exercises Task No. 3: Drat_3 Work procedure: Create a new source file and save it to the folder named “Drat_3” under the “Drat_3.asm” name.  Rewrite the source text from the supplied task printout to the editing window.  Check the finished source text and save it (rewrite the saved empty file).  Directives: #INCLUDE, BANKSEL  Instructions: BTFSC, BTFSS, CALL, RETURN  Testing of bit status by means of the BTS instruction  Work with subroutines

Practical exercises Task No. 3: Drat_3  Create a new project (use the procedure from chapter 11):  Project name: Drat_3.mcp, folder Drat_3.  Insert the source file Drat_3.asm.  Check and confirm the correctness of the assignment.  Save the project.

Practical exercises Task No. 3: Drat_3  Connect the MPLAB ICD-2 debugger to the USB port of the computer.  Connect an instruction board (to the ICD-2) and connect the supply voltage of 9V to the instruction board.  Carry out the necessary setups and checks.  Translate the program (Ctrl F10), eliminate possible errors.

Practical exercises Task No. 3: Drat_3  Launch the program (F9).  Check the correct function of the program:  Press any button on the instruction board (except the Reset button).  Check whether the corresponding LED diode is switched on when the button is pressed.  Try out how the program reacts when more buttons are pressed at the same time.  If the program does not work according to predictions, find the error by means of the procedures which were tried before and correct it.

Practical exercises Task No. 3: Drat_3  By means of a step-by-step operation (F7, F8), go through the program line after line and watch the behaviour of the program in individual steps.  Focus on the BTFSS instruction and on the way how program branching is implemented.  Notice how the mechanism of subroutine calling and the return from a subroutine works.  Switch over to the MPLAB-SIM mode.  From the “View” menu, select “Hardware Stack”.  In “Stack”, watch how the system of return addresses works during subroutine calling and during the return (from a subroutine).

Practical exercises A programmer´s nightmare – instructions BTFSS, BTFSC  Bit test of a selected register  Skip of the following program line according to the test result

Summary of the subject matter - exercises  Have you noticed any change in the behaviour of the Drat_3 program in comparison with the Drat_1 and Drat_2 programs?  If so, are you able to explain its cause?  Find a proper change in the program listing and explain it!

Summary of the subject matter - exercises  Explain the function of this writing: #define TL1 PORTA,0.  What is the instruction for return from a subroutine?  Can the GOTO instruction be used for return from a subroutine in some cases?  What is so-called “return address”? Where is it saved?  Explain the function of the “STACK” register and the function of the return address system for subroutine calling and for the return from a subroutine.

 Datasheet Microchip PIC16F882/883/884/886/887 DS41291E (  Microchip.com: Getting Started with PICmicro MCUs  Microchip.com: MPLAB IDE User’s Guide  Microchip.com: Quick Guide to Microchip Development Tools References

Appendices  Appendix No. 3: Source text listing of the “Drat_3” program.  Appendix No. 3, necessary to be translated in Notepad.