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EX5: Designing a microcontroller-based one minute timer

EX 5 DIGITAL CIRCUITS AND SYSTEMS

A one minute timer

1.1 Cooperative groupTEAM NUMBER: ___________

DUE DATE: ________________ 1st review due date: ________________

STUDY TIME:

Study time

(in hours)

Group work Classroom and laboratory sessions

Sessions out of classroom

Individual Student 1

Student 2

Student 3

STATEMENT:

My signature below indicates that I have (1) made equitable contribution to EX 5 as a member of the group, (2) read and fully agree with the contents (i.e., results, conclusions, analyses, simulations) of this document, and (3) acknowledged by name anyone outside this group who assisted this learning team or any individual member in the completion of this document.

Today’s date: __________________

Active members Roles: (reporter, simulator, etc.)

(1) ________________________________________ _______________

(2) _________________________________________ _______________

(3) _________________________________________ _______________

Acknowledgement of individual(s) who assisted this group in completing this document:

1

EPSC – CSD: Digital Circuits and Systems

(1) _______________________

(2) _______________________

1.2 Abstract Explain here the most significant developments, results or conclusions about the exercise. Use the remaining space in this sheet (200 words maximum).

(This section is mandatory. You must complete it in order to get a mark.)

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CONTENT

A one minute timer...............................................................................................................................................1

1.1 Cooperative group.....................................................................................................................................1

1.2 Abstract.....................................................................................................................................................1

1.3 Description................................................................................................................................................3

1.4 Topics........................................................................................................................................................3

1.5 Block diagram ad specifications for the one-minute timer.......................................................................4

1.6 Design flow and integrated development environment............................................................................4

1.6.1 Installing MPLAB..............................................................................................................................4

1.6.2 Installing the Micochip HITECH C lite C compiler.........................................................................4

1.7 PIC16F87X microcontrollers....................................................................................................................5

1.7.1 Architecture.......................................................................................................................................5

1.7.2 PIC assembler: RISC instruction set.................................................................................................6

1.8 Visiting microcontroller portals................................................................................................................7

1.9 Project flux diagram and FSM-like programming style...........................................................................8

1.9.1 Attending peripheral by interruptions...............................................................................................8

1.10 Other PIC16F87X peripherals...................................................................................................................9

1.10.1 LCD display......................................................................................................................................9

1.10.2 Timer 1..............................................................................................................................................9

1.10.3 Debugging the One Minute Timer.....................................................................................................9

1.11 Problem solution (títol 2)........................................................................................................................10

1.11.1 Part 1 (títol 3)..................................................................................................................................10

1.12 References...............................................................................................................................................11

1.13 Study plan to solve the exercise..............................................................................................................12

1.14 Topics and activities checklist................................................................................................................13

1.15 Grading grid............................................................................................................................................13

1.16 Questions in solving EX 5.......................................................................................................................13

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1.3 DescriptionThis exercise will establish the basics for working with microcontrollers for the remaining of the term. Instead of continuing Chapter III trying for instance to design our own microprocessor like many books in VHDL does, we are going to buy a commercial one and program it using assembler or C. Therefore, the idea is to replace “hardware programming” by software programming.

Today the more available microprocessors and the easy to use and learn ones are placed inside a microcontroller, which consist of a complete computer architecture in a single chip: microprocessor, data and program memory and input/output peripherals.

There are a wide range of commercial microcontrollers to choose from in order to learn the basics and start applying them to build simple applications. We have decided to pick the PIC16F family of flash microcontrollers from Microchip, one of the leading vendors.

This exercise will consist in developing a simple application like a one minute timer, using the input/output programmable ports, the timer/counter T0 to emulate the FSM clock, and some other 1PIC16F877A peripherals such as the LCD display and the Timer 1 controlled via polling or by interruptions.

The idea is to develop your first projects using C, the Proteus VSM virtual laboratory simulator, and a standard training board from Microchip like the PICDEM2 PLUS for prototyping the final design. Low level assembler language will be optional in case of any of you were interested.

1.4 Topics The following topics have been listed from the course’s specific and cross-curricular learning objectives 1: #13, #14. After studying Chapter 4 and successfully completing all the assignments in this task, you will be able to:

------------- Part 1: The general theory -------------

1. Identify and list commercial microcontrollers and their manufacturers.

2. Search books and the Internet to analyse information about microcontroller chips and their applications (web portals or electronic magazines on the subject of microcontrollers).

3. Explain the basics of a microcontroller-based embedded system.

4. Draw the typical design flow for a microcontroller-based application: concept, hardware, program flow diagrams, coding in assembler or C, Proteus VSM simulation, prototype using evaluation board, verification, in-circuit debugging or microcontroller emulation, PCB design and production.

5. Analyse the architecture of an 8-bit microcontroller like the PIC16F877A and describe their main blocks and peripherals.

6. Explain why a microprocessor (CPU) can be considered a programmable dedicated processor from Chapter III. Explain the roles of the EEPROM program memory and the RAM memory.

7. Explain the way to program I/O ports.

8. Explain the way to program the Timer0.

1 http://epsc.upc.edu/projectes/ed/CSD/units/Guia_docent_E1_v2.pdf

4

http://epsc.upc.edu/projectes/ed/CSD/units/Guia_docent_E1_v2.pdf


9. Analyse simple applications in assembler or C and deduce the program flowchart from the written code.

------------- Part 2: Analysis of an application designed in FSM style -------------

10. Analyse the Heads or Tails game, an example on programming in FSM style:

a. Plan a microcontroller application as if it were a simple FSM or a dedicated processor from Chapters II and III respectively. This is:

i. General schematic or top block diagram.

ii. Internal architecture using components and signals (and control unit + datapath if it is the case)

iii. State diagram for the FSM

b. Explain the role of Timer0 as the FSM clock generator.

c. Draw a program flowchart for every function (interrupt service routine, output logic, future state logic)

d. Convert the program flowchart in C (or in assembler, if it were the case)

e. Run the application using the virtual PICDEM 2 plus board.

f. Download the configuration code to the training board, using for example the In Circuit Debugger/programmer ICD2, and measure and characterise the project using laboratory instrumentation.

------------- Part 3: Your own design -------------

------------- Part 2: Analysis of an application designed in FSM style -------------

11. Plan and develop through the design flow an example application such as a one minute digital timer using C, the PIC16F877A, and the PICDEM 2 plus board. Use in this project other peripherals like the LCD display and the Timer 1.

1.5 Block diagram ad specifications for the one-minute timera) Invent the block diagram for a one minute timer based on a PIC16F877 microcontroller and the hardware

available at the PICDEM 2plus board.

Minimum specifications must include:

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- Power supply: 5 V (from a 9 V battery or from the power mains using a voltage regulator)

- PIC16F877A microcontroller.

- Hardware platform: PICDEM 2 plus board

Inputs:

- A pushbutton to set time in seconds (TimeSet). If pressed, the timer counts up at 2 Hz rate until the maximum of 59 s is reached.

- A pushbutton to start the down counting from the initial time displayed in the LCD (Trigger).

Outputs:

- A 2-rows LCD display (based on the Hitachi HD44180 chip) to show the timer count and messages.

- An alarm LED which turns on when the timer count reaches zero. After 15 s, it turns off.

- A buzzer output which also generates a sound 2.5 kHz signal when the count reaches zero. After 15 s, it turns off as the LED.

First of all, invent your block diagram as if it where a dedicated processor from Chapter III, thus, considering a control unit and a datapath. Then, annotate all signals and try to deduce the FSM state diagram.

1.6 Design flow and integrated development environment1.6.1 Installing MPLAB

b) Once having downloaded and installed the latest MPLAB software version from the Microchip web page, run a sample example written in assembler and explain the main procedures involved in the design process. Our web site contains examples from previous terms.

1.6.2 Installing the Micochip HITECH C lite C compiler

c) Learn about the way to install the free C compiler MPLAB plug-in and run a sample example written in C from the web and explain its advantages and drawbacks with respect a similar project written in assembler.

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Fig. 1 Typical design flow for microcontroller or embedded systems

1.7 PIC16F87X microcontrollers 1.7.1 Architecture

d) Study the PC16F877 datasheet to find answers for the following questions related to the basic building blocks which are represented in Fig. 2.

http://epsc.upc.edu/projectes/sed/SED/unitats/unitat_2_3/DataSheet_PIC16F87XA.pdf

1. Explain the differences between Harvard and Von Neumann microprocessor architectures.

2. Explain what the microcontroller flash program memory is.

3. Explain what the stack memory is and how it is used for.

4. Explain the main characteristics of the Bank0 and Bank1 of the RAM memory.

5. How many clock cycles are required for executing an instruction in assembler?

6. Describe the fashion in which the following assembler instructions are executed and the resources involved

INCF PORTA,F (F = 1, PORTA = 05h)

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http://epsc.upc.edu/projectes/sed/SED/unitats/unitat_2_3/DataSheet_PIC16F87XA.pdf


DECFSZ PORTB,W (W = 0, PORTB = 06h)

7. Which is the main architectural difference between 8/16/32 bits microprocessors?

8. Which are the functions of the FLASH (ROM) memory and the RAM registers?

Fig. 2 PIC16F877 architecture

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1.7.2 PIC assembler: RISC instruction set

e) Analyse the disassemble listing of the Heads and Tails game. As an example to show the way you have understood PIC structure and its assembler language (see Fig. 3), explain some of the assembler instruction found in the listing and how a C function is converted into assembler instructions by the C compiler.

Fig. 3 PIC16F877 instruction set

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1.8 Visiting microcontroller portals f) Read information about other manufacturers’ microcontrollers2 and list Internet addresses for accessing

and gathering information for each 8-bit microcontroller.

g) Visit Internet portals in Fig. 4 and make a similar list devoted to electronic magazines, like EDN, which nowadays are the general source of information for being updated with reference to electronics engineering in general and microcontrollers in particular.

Fig. 4 Typical Internet microcontroller portals for searching information

1.9 Project flux diagram and FSM-like programming styleh) Explain the programming strategy and some program flowcharts from the Heads or Tails game.

1.9.1 Attending peripheral by interruptions

i) Explain the way the Timer0 is programmed and the functionally of its configuration registers. Explain schematic in Fig. 5 to handle interrupts to the single PIC interrupt vector.

2 For instance: EX4 at http://epsc.upc.edu/projectes/sed/SED/grups_classe/07-08_Q1/2AT4/07-08-Q1-2AT4.htm

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http://epsc.upc.edu/projectes/sed/SED/grups_classe/07-08_Q1/2AT4/07-08-Q1-2AT4.htm

http://www.programmersheaven.com/


Fig. 5 Interruption scheme for PIC16F87X microcontrollers

j) Explain the main function main() and what it is used for.

1.10 Other PIC16F87X peripherals k) Invent a state diagram for the one-minute timer (as if it were to be designed in Chapter III as a dedicated

processor using VHDL). List the components that will be involved in the project: One-second time base, BCD up and down counter, registers, code converters, etc…

l) Write the programme flowchart for the one-minute timer. Follow a finite state machine coding style, thus remembering and using again Chapter I, II and III concepts and topics, even if you are writing software code instead of configuring hardware. FSM-style programming will be the only one permitted in the course, in order to standardise procedures, facilitate class discussions and assignments’ assessment. You might consider that such limitation to your creativity may be seen as a drawback. However, it is indeed, a great advantage in many other aspects. Find information on how to write software following a state machine style, in portals such as the ones listed in Fig. 4, in our own web resources and topic units, or at the Microchip applications' notes.

Remember that before attempting to code in assembler (or in C), a program flow diagram (or program flowchart) must be sketched specifying program sequence, operations and routines.

In this section, some of the most common PIC16F peripherals will be studied. The procedure will be very similar for all of them: firstly, the hardware diagrams; secondly, the bits and registers that are in charge of the peripheral commanding; and finally, the explanation of a sample C program in charge of handling the peripheral.

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1.10.1 LCD display

m) Deduce from the Heads and Tails example the way to include LCD display into your projects. List the C functions which allow handling the display.

1.10.2 Timer 1

n) Deduce from the datasheet, books and web portal the way to interface the Timer1 so that it can be used in your One Minute Timer application to count seconds in real time.

1.10.3 Debugging the One Minute Timer

o) Build the final project consisting of all the C and source and header files and debug it using the PICDEM 2plus virtual board.

p) Program the chip and perform laboratory measurements to characterise your prototype.

-------------------------------------------------------------------------------

We will leave for your next application project (AP), the study and use of other microcontroller peripherals such as Timer 2, PWM, CCP, A/D, UART, Data EEPROM, I2C, etc..

Optional: Assembler example to initialize and use I/O ports:

Problem description: Incrementing a binary counter clicking a pushbutton (solving button bouncing effect) See PICDEM2 board first tutorial example at:

http://epsc.upc.edu/projectes/sed/unitats/unitat_2_5/picdem2.zip

Circuit schematic captured in Proteus-VSM

Flux diagram

Assembler code with comments to describe the main procedures

Proteus-VSM simulation

Do not modify the text from page 3 to page 9

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http://epsc.upc.edu/projectes/sed/unitats/unitat_2_5/picdem2.zip


1.11 Problem solution (títol 2)1.11.1 Part 1 (títol 3)

Part 1.1 (títol 4)

És necessari que seguiu aquestes indicacions per qualsevol dels vostres documents en aquesta assignatura. Aprendre-les forma part de la competència de comunicació escrita. Adapteu els vostres documents al format subministrat per aquesta plantilla.

Si alguna indicació o format no l’acabeu d’entendre bé, pregunteu-nos-ho o aclariu els dubtes, però no lliureu mai res que no compleixi aquestes indicacions perquè no us ho corregirem i perdreu el temps.

Afegiu aquí el vostre text (estil normal) encapçalat amb títols (Títol 2 i 3 i 4), amb figures (estil “llegenda” o “epígrafe”) i referències creuades en el text com aquesta Fig. 6 (és una referència creuada a la llegenda, veureu que surt en color gris quan la cliqueu) a les figures que inseriu. Fixeu-vos que la primera vegada que obrireu aquest document en Word 2007, no us sortirà aquesta llegenda “Fig.”, així que haureu de crear-ne una, i després, encara que la esborreu,ja us quedarà la referència. Veureu també que la numeració de les figures és un paràmetre automàtic. Si seleccioneu tot el document, i premeu “F9” actualitzareu tota la numeració.

També l’índex de la pag. 2 és completament automàtic. Es genera sol ( a partir de referències, índex de continguts, Inseriu un índex de continguts) i s’actualitza sol a partir també de “F9” havent seleccionat tot el text de document. És possible que la primera vegada que l’actualitzeu desaparegui. No passa res, simplement cal tornar-lo a generar a partir del menú referències i taula de contingut.

Fixeu-vos en la Fig. 6. Les imatges han d’estar centrades i alineades amb el text. Si voleu posar un parell d’imatges a la mateixa línia, inseriu primer una taula d’un parell de columnes i tot seguit feu invisibles les vores. El millor que podeu fer és “cut & paste” de la pròpia taula que veieu, i, canviar les figures per les vostres.

Feu referència també en el text a les fonts bibliogràfiques o de web que consulteu d’aquesta manera [1] (és una referència creuada a l’element numerat [1]). Expliqueu perquè les heu consultat i quina informació útil heu trobat.

Per corregir la primera versió del vostre treball, no imprimiu ni lliureu des de les pàgines 3 a la 5. És l’enunciat del problema. Sols cal que imprimiu les 2 primeres pàgines que contenen els detalls personals, el resum i l’índex, i a partir d’aquesta mateixa pàgina 6. Però feu-ho amb la numeració correcta. És a dir, treballeu sempre sobre aquest document, i en tot cas, importeu altres textos que tingueu cap a aquest mateix document i formateu-los correctament.

Insistim sobre això mateix: treballeu sempre sobre aquest mateix fitxer per preparar la vostra solució. Així usareu tots els estils i formats que ja té predefinits aquest document.

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Fig. 6 Exemple de peu de figura que segueix la numeració de l’enunciat (llegenda).

Heu d’instal·lar els correctors ortogràfics en català, espanyol i anglès en el vostre paquet d’eines office. I sobretot, corregir qualsevol error mentre escriviu. Si treballeu això estalviareu molta feina als vostres companys i instructors.

1.12 References Modify or add new references to this section. Follow the same format.

[1] http://epsc.upc.edu/projectes/ed/ . Comment: Course wed page where to find a lot of resources for the course. Specially, materials from previous editions. Read the section on theory about digital systems. [visited 12/2009]

[2] Brown,S., Vranesic, Z., “Fundamentals of digital logic with VHDL design”, McGraw-Hill, 2005. Comment: Figure 1. 7 contains an example of design flow for logic circuits and Figure 2.29 the structure of a typical CAD/EDA system.

[3] An image to define a concept map: http://redie.uabc.mx/contenido/vol2no1/art-11-eng/contenido-ruiz-figura1.png

- Before delivering the exercise think in adding your own sources and references

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http://redie.uabc.mx/contenido/vol2no1/art-11-eng/contenido-ruiz-figura1.png

http://redie.uabc.mx/contenido/vol2no1/art-11-eng/contenido-ruiz-figura1.png

http://epsc.upc.edu/projectes/ed/


1.13 Study plan to solve the exercise Establish a study plan, a task distribution scheme and other requirements to succeed in producing a good solution when working cooperatively: flux diagrams, concept maps, schematics, tables, pictures, etc.

(This section is mandatory. It must be filled in order to get a mark.)

15


1.14 Topics and activities checklist

Topics Activities

Group member in

charge Comments

1 2 3

Part 1: The general theory

1. Identify and list commercial microcontrollers and their manufacturers

2. Search books and the Internet to analyse information about microcontroller chips and their applications (web portals or electronic magazines on the subject of microcontrollers).

3. Explain the basics of a microcontroller-based embedded system.

4. Draw the typical design flow for a microcontroller-based application: concept, hardware, program flow diagrams, coding in assembler or C, Proteus VSM simulation, prototype using evaluation board, verification, in-circuit debugging or microcontroller emulation, PCB design and production.

5. Analyse the architecture of an 8-bit microcontroller like the PIC16F877A and describe their main blocks and peripherals.

6. Explain why a microprocessor (CPU) can be considered a programmable dedicated processor from Chapter III. Explain the roles of the EEPROM program memory and the RAM memory.

7. Explain the way to program I/O ports.

8. Explain the way to program the Timer0.

9. Analyse simple applications in assembler or C and deduce the program flowchart from the written code.

Part 2: Analysis of an application designed in FSM style

10. Analyse the Heads or Tails game, an example on programming in FSM style:

a. Plan a microcontroller application as if it were a simple FSM or a dedicated processor from Chapters II and III respectively. This is:

i. General schematic or top block diagram.

ii. Internal architecture using

16


components and signals (and control unit + datapath if it is the case)

iii. State diagram for the FSM

b. Explain the role of Timer0 as the FSM clock generator.

c. Draw a program flowchart for every function (interrupt service routine, output logic, future state logic)

d. Convert the program flowchart in C (or in assembler, if it were the case)

e. Run the application using the virtual PICDEM 2 plus board.

f. Download the configuration code to the training board, using for example the In Circuit Debugger/programmer ICD2, and measure and characterise the project using laboratory instrumentation.

------------- Part 3: Your own design -------------

Part 2: Analysis of an application designed in FSM style

11. Plan and develop through the design flow an example application such as a one minute digital timer using C, the PIC16F877A, and the PICDEM 2 plus board. Use in this project other peripherals like the LCD display and the Timer.

1.15 Grading grid Here you are the way the exercise could be grades.

Part 1

The theory

Part 2

Analysis of the Head or Tails game

Part 3

One minute timer design

Total

Scores 3p 2p 5p

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Self-assessment

Instructor’s grades

Do not forget to annotate your own self assessment before uploading the exercise at your site.

1.16 Questions in solving EX 5Write here your questions, comments, doubts, opinions, etc. Add more sheets if necessary to report your progress or comments though the exercise.

[Add something here. It’s impossible to deeply understand everything in this complex subject !] Use this space to reflect and conclude about the course/exercise or whatever related to the content…

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