Microchip Technology PICDEM™ Lab Development Board User’s Guide

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PICDEM™ Lab

Development Board

User’s Guide

Note the following details of the code protection feature on Microchip devices:

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• Microchip is willing to work with the customer who is concerned about the integrity of their code.

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Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.

Information contained in this publication regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer’s risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.

Trademarks

The Microchip name and logo, the Microchip logo, Accuron, dsPIC, K

EELOQ, KEELOQ logo, MPLAB, PIC, PICmicro,

PICSTART, rfPIC, SmartShunt and UNI/O are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.

FilterLab, Linear Active Thermistor, MXDEV, MXLAB, SEEVAL, SmartSensor and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A.

Analog-for-the-Digital Age, Application Maestro, CodeGuard, dsPICDEM, dsPICDEM.net, dsPICworks, dsSPEAK, ECAN, ECONOMONITOR, FanSense, In-Circuit Serial Programming, ICSP, ICEPIC, Mindi, MiWi, MPASM, MPLAB Certified logo, MPLIB, MPLINK, mTouch, PICkit, PICDEM, PICDEM.net, PICtail, PIC

logo, PowerCal, PowerInfo, PowerMate, PowerTool, REAL ICE, rfLAB, Select Mode, Total Endurance, WiperLock and ZENA are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.

SQTP is a service mark of Microchip Technology Incorporated in the U.S.A.

All other trademarks mentioned herein are property of their respective companies.

Printed on recycled paper.

Microchip received ISO/TS-16949:2002 certification for its worldwide headquarters, design and wafer fabrication facilities in Chandler and Tempe, Arizona; Gresham, Oregon and design centers in California and India. The Company’s quality system processes and procedures are for its PIC devices, Serial EEPROMs, microperipherals, nonvolatile memory and analog products. In addition, Microchip’s quality system for the design and manufacture of development systems is ISO 9001:2000 certified.

MCUs and dsPIC® DSCs, KEELOQ

code hopping

Chapter 1. Overview

1.1 Introduction ..................................................................................................... 5

1.2 Highlights ........................................................................................................ 5

1.3 PICDEM™ Lab Development Kit Contents .................................................... 5

1.4 PICDEM™ Lab Development Board Construction and Layout ...................... 6

1.5 Target Power .................................................................................................. 7

1.6 Connecting the PICkit™ 2 Programmer/Debugger ........................................ 8

1.7 Solderless Prototyping Area Strip Configuration ............................................ 9

Chapter 2. Getting Started

2.1 Introduction ................................................................................................... 11

2.2 Prerequisites ................................................................................................ 11

2.3 The Software Control Loop .......................................................................... 11

2.4 MPLAB

2.5 Installing the Included Lab Files ................................................................... 16

IDE Download Instructions ............................................................ 12

PICDEM™LAB DEVELOPMENT

BOARD USER’S GUIDE

Table of Contents

Chapter 3. General Purpose Input/Output Labs

3.1 Introduction ................................................................................................... 17

3.2 General Purpose Input/Output Labs ............................................................. 17

3.3 GPIO Output Labs ........................................................................................ 18

3.3.1 Reference Documentation ......................................................................... 18

3.3.2 Equipment Required for GPIO Output Labs .............................................. 18

3.3.3 PICDEM Lab Development Board Setup for GPIO Output Labs ............... 18

3.3.4 Lab 1: Light LEDs ...................................................................................... 19

3.3.5 Lab 2: Flash LEDs (Delay Loop) ............................................................... 25

3.3.6 Lab 3: Simple Delays Using Timer0 .......................................................... 29

3.3.7 Lab 4: Rotate LEDs ................................................................................... 34

3.4 GPIO Input Labs ........................................................................................... 38

3.4.1 Reference Documentation ......................................................................... 38

3.4.2 Equipment Required for GPIO Input Labs ................................................. 38

3.4.3 PICDEM Lab Development Board Setup for GPIO Input Labs ................. 38

3.4.4 Lab 5: Adding a Push Button ..................................................................... 39

3.4.5 Lab 6: Push Button Interrupt ..................................................................... 48

3.4.6 Lab 7: Push Button Interrupt-on-Change .................................................. 53

3.4.7 Lab 8: Using Weak Pull-Ups ..................................................................... 58

PICDEM™Lab Development Board User’s Guide

Chapter 4. Comparator Peripheral Labs

4.1 Introduction ................................................................................................... 61

4.2 Comparator Labs .......................................................................................... 61

4.2.1 Reference Documentation .........................................................................61

4.2.2 Comparator Labs .......................................................................................61

4.2.3 Equipment Required ..................................................................................61

4.2.4 Lab 1: Simple Compare .............................................................................62

4.2.5 Lab 2: Using the Comparator Voltage Reference ......................................64

4.2.6 Lab 3: Higher Resolution Sensor Readings Using a Single Comparator ...68

Chapter 5. Analog-to-Digital Converter Peripheral Labs

5.1 Introduction ................................................................................................... 75

5.2 ADC Labs ..................................................................................................... 75

5.2.1 Reference Documentation .........................................................................75

5.2.2 Equipment Required ..................................................................................75

5.2.3 Lab 1: Simple ADC ....................................................................................76

5.2.4 Lab 2: Audible Temperature Sensor ..........................................................85

Appendix A. Schematic

A.1 PICDEM Lab Development Kit Schematic ................................................... 91

PICDEMTM LAB DEVELOPMENT

BOARD USER’S GUIDE

Preface

NOTICE TO CUSTOMERS

All documentation becomes dated, and this manual is no exception. Microchip tools and documentation are constantly evolving to meet customer needs, so some actual dialogs and/or tool descriptions may differ from those in this document. Please refer to our web site (www.microchip.com) to obtain the latest documentation available.

Documents are identified with a “DS” number. This number is located on the bottom of each page, in front of the p age number. The numbering convention for the DS number is “DSXXXXXA”, where “XXXXX” is the document number and “A” is the revision level of the document.

For the most up-to-date information on development tools, see the MPLAB Select the Help menu, and then Topics to open a list of available on-line help files.

INTRODUCTION

IDE on-line help.

This chapter contains general information that will be useful to know before using the PICDEM

• Document Layout

• Conventions Used in this Guide

• Recommended Reading

• The Microchip Web Site

• Customer Support

• Document Revision History

DOCUMENT LAYOUT

This document describes how to use the PICDEM TMLab Development Board as a development tool to emulate and debug firmware on a target board. The manual layout is as follows:

• Chapter 1. “Overview ”

• Chapter 2. “Getti ng Started”

• Chapter 3. “Gener al Purpo se Inp ut/Ou tp ut Lab s”

• Chapter 4. “Comparator Periphera l Labs”

• Chapter 5. “Analog- to -Di gital Converter Peri phe ral Labs”

• Appendix A. “Schematic”

Lab Development Board. Items discussed in this chapter include:

PICDEMTM Lab Development Board User’s Gu ide

CONVENTIONS USED IN THIS GUIDE

This manual uses the following documentation conventions:

DOCUMENTATION CONVENTIONS

Description Represents Examples

Arial font:

Italic characters Referenced books MPLAB

Emphasized text ...is the only compiler...

Initial caps A window the Output window

A dialog the Settings dialog A menu selection select Enable Programmer

Quotes A field name in a window or

dialog

Underlined, italic text with right angle bracket

Bold characters A dialog button Click OK

N‘Rnnnn A number in verilog format,

Text in angle brackets < > A key on the keyboard Press <Enter>, <F1>

Courier New font:

Plain Courier New Sample source code #define START

Italic Courier New A variable argument file.o, where file can be

Square brackets [ ] Optional arguments mcc18 [options] file

Curly brackets and pipe character: { | }

Ellipses... Replaces repeated text var_name [,

A menu path File>Save

A tab Click the Power tab

where N is the total number of digits, R is the radix and n is a digit.

Filenames autoexec.bat File paths c:\mcc18\h Keywords _asm, _endasm, static Command-line options -Opa+, -Opa- Bit values 0, 1 Constants 0xFF, ‘A’

Choice of mutually exclusive arguments; an OR selection

Represents code supplied by user

“Save project before build”

4‘b0010, 2‘hF1

any valid filename

[options] errorlevel {0|1}

var_name...] void main (void)

{ ... }

IDE User’s Guide

1.1 INTRODUCTION

The PICDEM Lab Development Board supports Microchip’s 8, 14, 18 and 20-pin 8-bit MCUs including accommodation for PIC10F products in the 8-pin PDIP package. Dual-row expansion headers on either side of each socket provide connectivity to all pins on the connected PIC explore a relatively large number of application examples without making permanent modifications to the board. Components permanently mounted to the board are interfaced using expansion headers to the user’s application via jumper wires. A variable supply voltage allows user’s to supply voltages between 1.2V to 5V to each of the PIC MCU connection sockets.

1.2 HIGHLIGHTS

This chapter discusses:

• PICDEM™ Lab Development Kit Contents

• PICDEM™ Lab Development Board Construction and Layout

• Target Power

• Connecting the PICkit™ 2 Programmer/Debugger

• Solderless Prototyping Area Strip Configuration

PICDEMTM LAB DEVELOPMENT

BOARD USER’S GUIDE

Chapter 1. Overview

MCU. A solderless prototyping area allows the user to

1.3 PICDEM™ LAB DEVELOPMENT KIT CONTENTS

The PICDEM™ Development Kit contains the following items:

1. The PICDEM™ Lab Development Board

2. Lab component kit including:

• (1) PIC16F616 DIP

• (1) PIC12F615 DIP

• (4) 10kΩ Resistors

•(4) 1kΩ Resistors

• (8) 470Ω Resistors

• (4) 220Ω Resistors

• (4) 100Ω Resistors

• (1) 10kΩ NTC Thermistor

• (4) Green LEDs

• (4) Red LEDs

• (4) 1N4148 Diodes

•(2) 0.1μF Capacitors

•(2) 1μF Capacitors

•(2) 10μF Capacitors

• (4) Push buttons

• (10) 5” Jumper Wires

• (10) 3” Jumper Wires

PICDEMTM Lab Development Board User’s Gu ide

• (10) 1” Jumper Wires

• (4) IRFD9020 P-CH MOSFETs

• (4) IRFD010 N-CH MOSFETs

• (2) 100kΩ Potentiometers

3. PICkit™ 2 Programmer/Debugger with USB Cable

4. CD-ROM including:

- “PICDEM™ Lab Development Board User’s Guide and Labs” (DS41369)

- “PIC16F631/677/685/687/689/690 Data Sheet” (DS41262)

- “Introduction to MPLAB MCU Family Lite Mode Compiler Tutorial” (DS41322)

- Timer: Timer0 Tutorial (Part 1) (DS51682)

- Timer: Timer0 Tutorial (Part 2) (DS51702)

1.4 PICDEM™ LAB DEVELOPMENT BOARD CONSTRUCTION AND LAYOUT

The Low Pin Count USB Development Board and populated components are shown in Figure 1-1.

FIGURE 1-1: PICDEM™ LAB DEVELOPMENT BOARD

IDE and HI-TECH C® PRO for the PIC10/12/16

1. PICkit™ 2 Programmer/Debugger Connection Headers (J13, J12 and J6)

a) J13 dedicated to PIC b) J12 dedicated to PIC c) J6 dedicated to PIC

2. PICkit™ Serial Analyzer Connection Header (J11) and Receptacle (J15)

To use the PICkit™ Serial Analyzer, connect to appropriate PIC MCU expansion header using jumper wires from receptacle.

microcontroller socket U5

microcontroller socket U3

microcontroller socket U2

Overview

3. 32 kHz Crystal Oscillator (Y1) and Connection Header (J7)

4. V

DD Connect/Disconnect Jumpers (J3, J4, J5)

a) J3 jumper connects/disconnects V

b) J4 jumper connects/disconnects V

c) J5 jumper connects/disconnects V

5. Battery Clip Connection (BT1) for 9V Battery and Jumpers (J14)

J14 jumpers connect/disconnect battery terminals for use in future lab on battery

chargers.

6. 9 V

DC Supply Connector (J1) and Connect/Disconnect Jumper (J2)

7. Power ON Switch (SW1)

8. 8-Pin PDIP PIC10F MCU Socket (U5) and Bilateral Dual-Row Expansion

Headers (J10 and J18)

Dual-row expansion headers provide connectivity to each pin on the PIC10F206 MCU populating socket U5.

9. 5V Brushed DC Motor

10. 18-Pin PDIP PIC MCU Socket (U3) and Bilateral Dual-Row Expansion Head-

ers (J17 and J16)

Dual-row expansion headers provide connectivity to each pin on the PIC16F819 MCU populating socket U3.

11. 8, 14, 20-Pin PDIP PIC MCU Socket (U2) and Bilateral Dual-Row Expansion

Headers (J8 and J9)

Dual-row expansion headers provide connectivity to each pin on the PIC16F690 MCU populating socket U2.

12. Solderless Prototyping Area

13. Bilateral Dual-Row Supply Headers (J22 and J23)

Provide both V

DD and VSS connectivity bilaterally to the solderless prototyping

area.

14. 0.2 Watt, 8-Ohm Speaker (LS1) with Connection Header (J19)

J19 connector used to connect speaker LS1 to user application using jumper wires.

15. Battery Positive (CP+) and Negative (CP-) Connection Header (J26)

Provides connectivity of positive and negative battery terminals to the user application using jumper wires.

16. Variable V

DD Potentiometer (R1)

Potentiometer used to vary PIC MCU supply voltage from approximately 1.3V to approximately 5V.

DD1 supply to PIC16F690 MCU in socket

DD2 supply to PIC16F819 MCU in socket

DD3 supply to PIC10F206 MCU in socket

1.5 TARGET POWER

The PICDEM™ Lab Development Board can be powered in one of three ways:

1. Using a 9-12 V

(MIcrochip part #AC162039 recommended) Ensure that connect/disconnect jumper J2 is in place.

DC power supply connected to connector J1

PICDEMTM Lab Development Board User’s Gu ide

2. Using a 9V battery connected to connector BT1 Ensure that connect/disconnect jumpers J14 are in place.

3. A PICkit™ 2 Programmer/Debugger connected to any one of the three PICkit™ Programmer/Debugger connectors J13, J12 and J6 (recommended for low-power applications only).

Note: When using the PICkit™ 2 Programmer/Debugger as the power source,

the variable V

When using methods 1 or 2, each PIC connect/disconnect jumper that, when in place, enables the positive supply voltage to the respective V

DD pins. The VDD jumpers connect to the following PIC

troller sockets:

DD1 (J3) connects/disconnects supply voltage to the PIC

1. V populating U2.

2. V

DD2 (J4) connects/disconnects supply voltage to the PIC

populating U3.

3. V

DD3 (J5) connects/disconnects supply voltage to the PIC

populating U5.

Using methods 1 or 2 enables the use of the variable V supply voltages from approximately 1.3 to 5V. Rotating the potentiometer clockwise will raise the supply voltage while rotating the potentiometer counterclockwise will decrease the supply voltage.

DD potentiometer (R1) will not vary the supply voltage.

microcontroller has an associated

microcontroller

DD potentiometer (R1) to control

microcon-

1.6 CONNECTING THE PICkit™ 2 PROGRAMMER/DEBUGGER

The three PIC® microcontrollers populating sockets U5, U3 and U2 have their own PICkit™ Programmer/Debugger (ICSP™) connectors so that each can be programmed or debugged individually. The ICSP™ connect to the following PIC controller sockets:

1. ICSP1 (J6) connects to the PIC

2. ICSP2 (J12) connects to the PIC

3. ICSP3 (J13) connects to the PIC

The PICkit™ Programmer/Debugger connects to the ICSP™ connector as shown in Figure 1-2.

microcontroller populating U2.

microcontroller populating U3.

microcontroller populating U5.

micro-

Overview

ICSP™ CONNECTOR

PICkit™ Programmer/Debugger

Denotes Pin 1

Solderless Prototyping Area

Showing Strip Connections

FIGURE 1-2: CONNECTING THE PICkit™ PROGRAMMER/DEBUGGER TO

AN ICSP™ CONNECTOR

The PICkit™ 2 Programmer/Debugger is then connected to an available USB port on the PC using the included USB cable.

1.7 SOLDERLESS PROTOTYPING AREA STRIP CONFIGURATION

The solderless prototyping area contains a variety of strips under the perforated plastic block. These strips “short” vertical rows of holes together as shown in Figure 1-3.

FIGURE 1-3: SOLDERLESS PROTOTYPING AREA STRIP

CONFIGURATION

PICDEMTM Lab Development Board User’s Gu ide

NOTES:

PICDEMTM LAB DEVELOPMENT

main()

Loop Forever

Timing()

Initialize()

Get_Inputs()

Decide()

Do_Outputs()

Chapter 2. Getting Started

2.1 INTRODUCTION

This chapter is intended to prepare the reader to complete the labs in the remaining chapters of this user’s guide.

2.2 PREREQUISITES

The labs contained within this lab manual assumes the user:

1. Has a basic understanding of the C programming language.

2. Understands basic circuit analysis.

3. Has completed or understands the concepts contained within the introductory

tutorial: “Introduction to MPLAB MCU Family Lite Mode Compiler Tutorial” (DS41322B) provided on the

accompanying CD-ROM.

2.3 THE SOFTWARE CONTROL LOOP

BOARD USER ’S GUIDE

IDE and HI-TECH C® PRO for the PIC10/12/16

The labs used in this user’s guide implement a software control loop in various configurations but always in the same sequence as shown in Example 2-1.

FIGURE 2-1: MAIN() SOFTWARE CONTROL LOOP FLOWCHART FOR

USED IN LABS

Each block of the software control loop represents a function that organizes tasks into

logical, organized groupings that are called from the main function (main()). Notice

the Initialize() is called only once while the remaining functions are executed repeatedly. This method organizes the embedded firmware application into a logic sequence of events:

PICDEMTM Lab Development Board User’s Gu ide

void main(void)

{

Initialize(); //Initialize the relevant registers

while(1)

{

Decide();//Make any decisions

Do_Outputs(); //Perform any outputs

Timing();//Sets execution rate of the

//Software Control Loop

}

1. Initalize():

- Initializes the microcontroller, the peripherals used in the application and any global variables used by multiple functions.

2. Get_Inputs():

- Obtains any input information either on-chip (from internal registers, etc...) or off-chip (pin voltage levels).

3. Decide():

- Makes decisions based on the input information gathered in the previous function to manipulate global variables.

4. Do_Outputs():

- Based on the decisions made in the previous function, this function outputs data onto the pins of the microcontroller or to registers within the device.

5. Timing():

- This function determines how fast the software control loop executes.

Example 2-1 shows a typical main() calling the various functions that make up the software control loop.

EXAMPLE 2-1: TYPICAL SOFTWARE CONTROL LOOP MAIN() USED IN

LABS

An infinity loop will be used by all labs in this user’s guide created using a while loop that repeatedly call the functions within the curly braces as long as there is power to the microcontroller.

Global variables are used wherever needed in lieu of passing variables between functions.

2.4 MPLAB® IDE DOWNLOAD INSTRUCTIONS

The following steps outline how to download the latest version of the MPLAB IDE and HI-TECH C mended that all open programs and applications are closed to expedite the installation process.

PRO for the PIC10/12/16 MCU Families compiler. It is strongly recom-

Getting Started

1. Using a PC that is connected to the internet, navigate to the MPLAB® IDE down-

load page at the following url:

www.microchip.com/mplab

This page outlines the MPLAB IDE and also features downloadable plug-ins, User’s Guides and other useful information.

2. Scroll down to the Downloads section of the page and select the latest full

release zip file for MPLAB IDE vx.xx. (See Figure 2-2.)

FIGURE 2-2: MPLAB ZIP FILE

3. When prompted open the .zip file and extract all contents to a new folder named

something meaningful such as “MPLAB” created in a directory such as Desktop or another location easily accessible.

4. Once all files are extracted, navigate to the folder created and double click on the

Install_MPLAB_vxxx.exe file to start the installation process.

5. The MPLAB

proceed with the installation.

6. In the next window, read through the MPLAB IDE License Agreement and ensure

that the I accept the terms of the license agreement radio button is selected. Click Next>

7. In the Setup Type window select the setup type (complete is recommended for

new users) and click Next>

8. In the Choose Destination Location it is recommended to use the default direct

C:\Program Files\Microchip\. Click Next>

9. Accept the Application Maestro License agreement in the next window and click

Next>

to continue.

10. Click Next>

take several minutes to complete).

11. During the installation process, the user will be prompted to install the free

HI-TECH C the user install the compiler at this point. Select Yes to launch the installer. In the

installer window, click Next to continue. (See Figure 2-3.)

Tools x.xx Installation window should now be open. Click Next> to

to continue with the installation.

to continue.

in the Start Copying Files window to start the installation (this may

PRO for the PIC10/12/16 MCU Compiler. It is recommended that

PICDEMTM Lab Development Board User’s Gu ide

FIGURE 2-3: HI TECH INSTALLER WINDOW

12. In the next window, accept the terms of the license agreement and click Next to

continue. (See Figure 2-4.)

FIGURE 2-4: HI TECH LICENSE AGREEMENT

13. In the next window, select any components in addition to the HI-TECH C the PIC10/12/16 MCU Family Compiler to install (additional components are not

required to complete the labs in this user's guide) and click Next to continue.

(See Figure 2-5.)

Pro for

Getting Started

FIGURE 2-5: HI TECH COMPONENTS

14. In the next window, choose the language of preference, select the Add to

environment path radio button and click Next to continue. (See Figure 2-6.)

FIGURE 2-6: HI TECH LANGUAGE PREFERENCES

The installation process will now begin.

15. Once the installation is complete, a confirmation window will open. Select or

de-select the Read quick start gui de now? radio button and click Finish to

proceed. (See Figure 2-7.)

PICDEMTM Lab Development Board User’s Gu ide

FIGURE 2-7: HI TECH INSTALL CONFIRMATION

16. The MPLAB and prompt the user to restart the computer before using the software. To begin

using the tools, select the Yes, I want to restart my computer radio button and click Finish to end the installation process and restart the computer.

Following restart, the user will be given the option to view a variety of documentation.

To view a document, simply highlight and click View Selected File.

The MPLAB Compiler are now both installed and ready to use. The user is now ready to complete the labs included in this user’s guide.

Note: A comprehensive introduction to the “HI-TECH C® PRO for the

Tools Install Shield Wizard Complete window should soon open

IDE and HI-TECH C® PRO for the PIC10/12/16 MCU Family Lite Mode

PIC10/12/16 MCU Family Lite Mode Compiler Tutorial” (DS41322) is

provided on the accompanying CD-ROM.

2.5 INSTALLING THE INCLUDED LAB FILES

The PICDEM™ Lab Development Kit CD-ROM includes a .zip file called PICDEM_Lab.zip. This file provides a location for the user to save any projects created while completing the labs in this user's guide and contains solutions for each lab in a folder labeled solution. To install this folder, simply extract the contents of the .zip file to the C:\ directory.

Note: Lab folders must be installed to the C:\ to be used by the MPLAB IDE.

Chapter 3. General Purpose Input/Output Labs

3.1 INTRODUCTION

The following labs cover some of the fundamental features of the General Purpose Input/Output (GPIO) peripherals available on the PIC16F690. As the name implies, these peripherals are used for general purpose applications that can monitor and control other off-chip devices. Some PIC peripherals on-chip including the PIC16F690 used in the following labs. Therefore, the PORTx naming convention is used. Available ports on the PIC16F690 are:

•PORTA

•PORTB

•PORTC

Reading through the data sheet highlights some of the unique characteristics associated with each port and the reader is encouraged to explore these in greater detail once comfortable with the labs in this user’s guide. The labs will focus on two of the port peripherals: PORTC and PORTA. Labs will be naturally divided into two sections since these are General Purpose Input/Output peripherals:

• Output Labs

• Input Labs

Output labs will introduce the reader to concepts necessary to configuring these peripherals for output to off-chip devices using applicable registers by lighting 8 LEDs connected to the PORTC pins

The Input labs will then add a push button interfacing to one of the PORTA pins to highlight concepts necessary for configuring these peripherals to receive information from off-chip devices. Finally, interrupts will be used to optimize the application for different purposes.

PICDEMTM LAB DEVELOPMENT

BOARD USER’S GUIDE

microcontrollers have multiple GPIO

3.2 GENERAL PURPOSE INPUT/OUTPUT LABS

• Output Labs:

- Lab 1: Light LEDs

- Lab 2: Flash LEDs (Delay Loop)

- Lab 3: Simple Delays Using Timer0

- Lab 4: Rotate LEDs

• Input Labs:

- Lab 5: Adding a Push Button

- Lab 6: Push Button Interrupt

- Lab 7: Push Button Interrupt-on-Change

- Lab 8: Using Weak Pull-ups

PICDEMTM Lab Development Board User’s Gu ide

1 2 3 4 5 6 7 8 9

20 19 18 17 16 15 14 13 12

RC0 RC1 RC2

RC3

RC4

RC5

RC6

RC7

J9J8

R8 470Ω

R4 470Ω

R7 470Ω

R6 470Ω

R5 470Ω

R3 470Ω

R2 470Ω

R1 470Ω

LED8 LED7 LED6 LED4 LED3 LED2 LED1LED5

3.3 GPIO OUTPUT LABS

3.3.1 Reference Documentation

All documentation is available on the PICDEM™ Lab Development Kit accompanying CD-ROM.

• PIC16F690 Data Sheet (DS41262)

- Section 2.2.2.2: Option Register

- Section 2.2.2.3: Interrupt Control Register INTCON

- Section 4: I/O Ports

- Section 5: Timer0 Module

• Timers: Timer0 Tutorial (Part 1) (DS51628)

• Timers: Timer0 Tutorial (Part 2) (DS51702)

• “Introduction to MPLAB

Family Lite Mode Compiler Tutorial” (DS41322)

3.3.2 Equipment Required for GPIO Output Labs

To complete the labs in this section, the following components are required:

1. 8 – Light Emitting Diodes

2. 8 – 470Ω resistors

3. PIC16F690 populating socket U2

4. Assorted jumper wires

IDE and HI-TECH C® PRO for the PIC10/12/16 MCU

3.3.3 PICDEM Lab Development Board Setup for GPIO Output Labs

The GPIO output labs will require that the PICDEM Lab Development Board be configured as shown in Figure 3-1 using the components listed in the previous section.

FIGURE 3-1: PICDEM LAB SCHEMATIC FOR GPIO OUTPUT LABS

General Purpose Input/Output Labs

main()

Initialize()

Do_Outputs()

Loop Forever

Special care should be observed when connecting the LED jumper wires to the expansion headers surrounding the PIC16F690, as the PORTC pins are not in sequential order. The 470Ω resistors are used to limit the current across the LEDs to manufacturer specifications. Furthermore, the PIC16F690 Data Sheet electrical specifications (see Section 17.0) specify that each port pin should not source/sink more than 25 mA. The maximum output current sourced/sunk by all port pins combined should not exceed 200 mA. The 470Ω resistors keep all source current well within these specifications.

3.3.4 Lab 1: Light LEDs

3.3.4.1 NEW REGISTERS USED IN THIS LAB

To configure the peripherals used in this lab, the following registers are used:

1. PORTC Register: PORTC (Register 4-11 in Section 4 of the PIC16F690 Data

Sheet).

- 8-bit bidirectional port.

2. PORTC Tri-State Register: TRISC (Register 4-12 in Section 4 of the PIC16F690

Data Sheet).

- Configures corresponding bits in PORTC as either input or output.

3. Analog Select Register High and Analog Select Register Low: ANSELH and

ANSEL (Registers 4-4 and 4-3 in Section 4 of the PIC16F690 Data Sheet).

- Configure associated pins for analog or digital input signals.

3.3.4.2 OVERVIEW

This first lab demonstrates how to output data from the PORTC peripheral on the PIC16F690 to its associated pins. LEDs connected to PORTC pins will light when the associated pin is driven high (approx. V (approx. V need to be configured as output using the TRISC register. Also, PORTC pins RC0, RC1, RC2, RC3, RC6 and RC7 are configurable for both analog and digital signals. On start-up, any analog/digital functional pin is defaulted to analog. Therefore, this application will require that these pins be configured as digital by configuring the associated bits in the ANSEL and ANSELH analog select registers.

FIGURE 3-2: MAIN() SOFTWARE CONTROL LOOP FLOWCHART FOR

SS). The port peripherals will all default to input on start-up and will therefore

LAB 1

DD) or turn the LED OFF when driven low

PICDEMTM Lab Development Board User’s Gu ide

Figure 3-2 shows the software control loop that will be implemented in this lab. At device power-up, the first functional block called from the main() is Initialize(). This function will initialize the PORTC peripheral as follows:

• Clear the PORTC register data

• Configure the ANSEL and ANSELH bits so that all associated PORTC pins are

digital

• Configure the associated PORTC pins as all output using the TRISC register

Note: The PORT register should always be initialized to a known value before

configuring the associated TRIS bit. This avoids unexpected voltage levels on the associated pins since at start-up port bit values are unknown.

The next function called from main() is Do_Outputs(). This function will assign values to the PORTC register that will drive the associated pins high or low to light the LEDs connected.

3.3.4.3 PROCEDURE

The following steps will demonstrate how to create a new project in MPLAB

more in-depth tutorial is provided in the document “Introduction to MPLA B

HI-TECH C

(DS41322) included on the accompanying CD-ROM.

1. Open MPLAB IDE by selecting Start>Microchip>MPLAB IDE vX.XX>MPLAB IDE.

2. In the MPLAB IDE toolbar, select Project>Project Wizard....

3. The Welcome dialog box should now be open. Select Next> to proceed.

4. In the Step One: window, select the PIC16F690 from the Device: drop-down

menu and select Next>

PRO for the PIC10/12/16 MCU Family Lite Mode Compiler Tutorial”

to continue. (See Figure 3-3.)

IDE. A

IDE and

FIGURE 3-3: STEP ONE

5. In the Step Two: window, select the HI TECH Universal ToolSuite from the Active Toolsuite drop down menu. The window should now resemble Figure 3-4.

General Purpose Input/Output Labs

FIGURE 3-4: STEP TWO

6. In the Step Three: window, use the Browse button and navigate to a new folder

on the C:\ drive to store this project. Alternately, the reader may wish to use the C:\PICDEM_Lab\GPIO_Labs\GPIO_Lab1 folder created earlier. (See Figure 3-5.)

FIGURE 3-5: STEP THREE

7. In the Step Four: files are added to the project. A Lab_Template.c file has

been provided in the C:\PICDEM_Lab\Lab_Template.c directory that can be used as the basis for all labs in this manual. To use the Lab_Template.c file,

select it from the right menu and click the Add>> button. Click on the large letter

‘A’ that appears next to the added file in the right window until it becomes a ‘C’. This indicates that a copy of the Lab_Template.c will be included in the project directory. Otherwise, changes made to the file during the course of the lab will alter the original file.

Finally, rename the Lab_Template.c file in the right window to GPIO_Lab1.c by clicking on it three times to enable editing the name. The Step Four: window should

now resemble Figure 3-6. Click Next>

to continue.

PICDEMTM Lab Development Board User’s Gu ide

FIGURE 3-6: STEP FOUR

8. Finally, the Summary window should appear showing the selected device, the

tool suite and the new project file name. Click Finish to exit the Project Wizard.

FIGURE 3-7: SUMMARY

9. The MPLAB

visible, it can be opened by selecting View>Project

resemble Figure 3-8.

IDE Workspace should now be open. If the Project window is not

. The Project window should

General Purpose Input/Output Labs

//Clear PORTC to a known state PORTC = 0b00000000;

//Configure PORTC's ANALOG/DIGITAL pins as all Digital ANS4 = 0;//Associated with RC0 ANS5 = 0;//Associated with RC1 ANS6 = 0;//Associated with RC2 ANS7 = 0;//Associated with RC3 ANS8 = 0;//Associated with RC6 ANS9 = 0;//Associated with RC7

//Configure PORTC pins as all output //i.e. 1 = Input, 0 = Output TRISC0 = 0;//Make RC0 (pin 16) output TRISC1 = 0;//Make RC1 (pin 15) output TRISC2 = 0;//Make RC2 (pin 14) output TRISC3 = 0;//Make RC3 (pin 7) output TRISC4 = 0;//Make RC4 (pin 6) output TRISC5 = 0;//Make RC5 (pin 5) output TRISC6 = 0;//Make RC6 (pin 8) output TRISC7 = 0;//Make RC7 (pin 9) output

FIGURE 3-8: PROJECT WIN DOW

10. Double click on the GPIO_Lab1.c source file in the Project window to open.

11. Copy/paste the code in Example 3-1 into the Initialize() section labeled:

//ADD INITIALIZE CODE HERE

EXAMPLE 3-1: INITIALIZE() CODE FOR LAB 1

PICDEMTM Lab Development Board User’s Gu ide

RC0 = 1;//Make RC0 (pin 16) HIGH (approx. Vdd) RC1 = 0;//Make RC1 (pin 15) LOW (approx. Vss) RC2 = 1;//Make RC2 (pin 14) HIGH (approx. Vdd) RC3 = 1;//Make RC3 (pin 7) HIGH (approx. Vdd) RC4 = 0;//Make RC4 (pin 6) LOW (approx. Vss) RC5 = 1;//Make RC5 (pin 5) HIGH (approx. Vdd) RC6 = 0;//Make RC6 (pin 8) LOW (approx. Vss) RC7 = 1;//Make RC7 (pin 9) HIGH (approx. Vdd)

Initialize(); //Initialize the relevant registers

while(1) //Code within curly braces will loop forever {

Do_Outputs(); //Perform any outputs

}

12. Copy/paste the code in Example 3-2 into the Do_Outputs() section labeled: //ADD DO_OUTPUTS CODE HERE

EXAMPLE 3-2: DO_OUTPUT() CODE FOR LAB 1

13. Copy/paste the code in Example 3-3 into the main() section labeled: //ADD MAIN CODE HERE

EXAMPLE 3-3: MAIN() CODE FOR LAB 1

The project is now ready to compile and download to the PIC16F690.

14. Compile the project ensuring no errors.

15. Connect the PICkit™ 2 Programmer/Debugger to an available USB port on the PC and then to the ICSP™ connector ICSP1 (J6) on the PICDEM Lab Development Board. The PICkit 2 should recognize if a power source is not connected to the PIC16F690 and provide target power.

16. In the MPLAB™ IDE Project Workspace, select

Programmer>Select Programmer>PICkit 2

17. The PICkit 2 Programmer/Debugger toolbar should now be visible in the workspace as shown in Figure 3-9.

General Purpose Input/Output Labs

Legend:

1. Program the target device

2. Read target device memories

3. Read the target EEDATA memory

4. Verify the contents of the target device

5. Erase the target device memories

6. Verify that target memories are erased

7. Bring target MCLR

to VDD

8. Bring target MCLR to VIL

9. Re-establish PICkit 2 connection

1 2 3 4 5 6 7 8 9

R8 470Ω

R4 470Ω

R7 470Ω

R6 470Ω

R5 470Ω

R3 470Ω

R2 470Ω

R1 470Ω

LED8 LED7 LED6 LED4 LED3 LED2 LED1LED5

SSLED ON LED OFF

FIGURE 3-9: PICkit 2 PROGRAMMER/DEBUGGER TOOLBAR

8. Press button1 shown in Figure 3-9 to program the PIC16F690.

3.3.4.4 TESTING THE APPLICATION

Once programmed, the LEDs connected to the individual PORTC pins should now resemble the output shown in Figure 3-10.

FIGURE 3-10: LAB 1 LED OUTPUT

The solution for this project is located in the C:\PICDEM_Lab\GPIO_Labs\GPIO_Lab1\solution directory.

3.3.5 Lab 2: Flash LEDs (Delay Loop)

3.3.5.1 OVERVIEW

This lab implements a software delay to flash the LEDs connected to the PORTC pins on/off in 1 second intervals. As configured, the PIC16F690 executes 1 million instructions per second. At this rate, the software loop execution needs to be slowed down so that the LED flashing is visible to the eye. This is done using a delay routine within the Timing() functional block called from the main() software control loop as shown in Figure 3-11.

PICDEMTM Lab Development Board User’s Gu ide

main()

Initialize()

Do_Outputs()

Loop Forever

Timing()

TIMING()

Create two 8-bit variables:

• delay_var1 = 45571

• delay_var2 = 3

delay_var2 - 1 = 0

delay_var1 - 1 = 0

END

delay_var1 = 45571

YES

FIGURE 3-11: MAIN() SOFTWARE CONTROL LOOP FLOWCHART FOR

LAB 2

The Timing() delay routine is shown in Figure 3-12.

FIGURE 3-12: TIMING() DELAY ROUTINE FLOWCHART FOR LAB 2

Two variables are used delay_var1 and delay_var2. The delay_var2 is decremented by 1 each time delay_var1 is decremented from 45571 to 0. These values have been determined through trial and error using a test procedure detailed in the “Timers: Timer0 Tutorial (Part 1)” (DS51682.pdf) included on the PICDEM™ Lab Development Kit CD. This delay ties the up the processor for 1 second when using the 4 MHz internal oscillator.

The Initialize() configures the PORTC as follows:

•PORTC

- Set all bits in the PORTC register HIGH

- Configure all PORTC pins as digital outputs

General Purpose Input/Output Labs

//Set all PORTC bits HIGH (to a known state) PORTC = 0b11111111;

The Do_Outputs() changes somewhat from the previous lab by implementing the XOR operator to toggle the value in each PORTC bit location each time through the software loop. The XOR operator is implemented in code as follows: RCx ^= 1;

This translates to: “Make RCx equal to the current value in RCx XOR’d with 1”

When a value is XOR’d with itself, the result is ‘0’ (i.e., 1 XOR’d with 1 = 0, 0 XOR’d with 0 = 0). When a value is XOR’d with a value different than itself, the result is ‘1’ (i.e., 1 XOR’d with 0 = 1). Therefore, each time through the loop PORTC bits will toggle from 1-to-0 or 0-to-1 depending on its current value.

3.3.5.2 PROCEDURE

Using the code developed in the previous lab, make the following changes:

1. Copy/paste the code in Example 3-4 over the Initialize() code from the

previous lab.

Note: The reader may wish to create a new project as per the previous lab called

GPIO_Lab2.mcp

EXAMPLE 3-4: INITIALIZE() CODE FOR LAB 2

The only change from the previous lab is that the PORTC bits are all set high to 1.

2. Copy/paste the code in Example 3-5 over the Do_Outputs() code from the

previous lab to accommodate the XOR bit toggle.

PICDEMTM Lab Development Board User’s Gu ide

RC0 ^= 1;//XOR current RC0 value with 1 RC1 ^= 1;//XOR current RC1 value with 1 RC2 ^= 1;//XOR current RC2 value with 1 RC3 ^= 1;//XOR current RC3 value with 1 RC4 ^= 1;//XOR current RC4 value with 1 RC5 ^= 1;//XOR current RC5 value with 1 RC6 ^= 1;//XOR current RC6 value with 1 RC7 ^= 1;//XOR current RC7 value with 1

//--------DELAY 1second------------------------//Variable used in delay loop unsigned int delay_var1 = 45571; unsigned char delay_var2 = 3; //Nested while loops to implement a 1 second delay //Decrement delay_var2, if 0 jump out of loop while(--delay_var2) {

//Decrement delay_var1, if 0 jump out of loop while(--delay_var1);

}

Initialize(); //Initialize the relevant registers

while(1) {

Do_Outputs(); //Perform any outputs

Timing();//Sets execution rate of the

//Software Control Loop

}

EXAMPLE 3-5: DO_OUTPUT() CODE FOR LAB 2

3. Copy/paste the code in Example 3-6 into the Timing() section labeled: //ADD TIMING CODE HERE

EXAMPLE 3-6: TIMING() FOR LAB 2

4. Copy/paste the code in Example 3-7 over the main() code from the previous lab to incorporate the Timing().

EXAMPLE 3-7: MAIN() CODE FOR LAB 2

Compile the project. There should be no errors.

3.3.5.3 TESTING THE APPLICATION

Program the PIC16F690. The LEDs connected to the individual PORTC pins should now all flash on/off in 1 second intervals.

The solution for this project is located in the C:\PICDEM_Lab\GPIO_Labs\GPIO_Lab2\solution directory.

General Purpose Input/Output Labs

TMR0 Overflow Period = (4/FOSC) x 256 = 1 μSecond x 256 = 256 μSeconds

TMR0 Overflow Period = (4/FOSC) x 256 x prescaler

Using a 1:32 prescaler setting as an example and a 4 MHz internal oscillator

TMR0 Overflow Period = 1

μS x 256 x 32 = 8.192mS

3.3.6 Lab 3: Simple Delays Using Timer0

3.3.6.1 NEW REGISTERS USED IN THIS LAB

To configure the peripherals used in this lab, the following registers are used:

1. Timer0 Module Register: TMR0

- Holds a count value of the number of selected edge transition of a clock source.

2. OPTION Register: OPTION_REG (Register 5-1 in Section 5 of the PIC16F690 Data Sheet).

- Selects clock source used to increment TMR0 result register.

- Selects clock source edge transition to increment TMR0.

3. Software configurable prescaler to determine the number of clock source edge transitions before incrementing TMR0 register value.

4. Interrupt Control Register: INTCON (Register 2-3 in Section 2 of the PIC16F690 Data Sheet).

- Contains a flag that when 1, indicates a TMR0 register overflow has occurred.

3.3.6.2 OVERVIEW

To implement a more accurate delay, the Timer0 peripheral can be used. Timer0 is an 8-bit timer/counter that uses a clock source to increment an 8-bit register called TMR0. Since this register is 8 bits, it can increment up 2 (00000000 TMR0 overflows, a Timer0 Overflow Flag (T0IF) in the OPTION register is set to ‘1’. This register also features a prescaler that determines how many clock source cycles it takes to increment TMR0 by ‘1’. In this way, simply by tracking the T0IF, very accurate delays can be implemented. In this lab, the TMR0 register is configured to increment on the low-to-high transition of an available internal instruction clock on the PIC16F690. This internal instruction clock runs at the rate of the internal oscillator frequency F divided by 4. Therefore, when the PIC16F690 is configured to operate using the internal 4 MHz oscillator, this internal instruction clock runs at a rate of F

OSC/4 = 4MHz/4 = 1MHz. This is a period of 1/1MHz = 1 μS. If it is known that TMR0

increments every 1 μS, and it takes 256 internal instruction clock cycles to cause a TMR0 overflow (i.e., 0-255 inclusive), then Equation 3-1 can be derived:

- 111111112) inclusive then rollover or overflow back to ‘0’. Whenever

= 256 times or 010 - 25510

OSC

EQUATION 3-1: TMR0 OVERFLOW PERIOD USING FOSC/4

As mentioned, Timer0 also features a prescaler that can be configured to increment the value in TMR0 every 2, 4, 8, 16, 32, 64, 128, or 256 clock source transitions. Therefore, this feature can be added to Equation 3-1 to create Equation 3-2.

EQUATION 3-2: TMR0 OVERFLOW PERIOD WHEN INCLUDING THE

PRESCALER

PICDEMTM Lab Development Board User’s Gu ide

Desired TMR0 Overflow Period = (4/FOSC) x (256 - Preload Value) x prescaler

Using a 1:64 prescaler setting, a 4 MHz internal oscillator and requiring a 10 mS overflow period:

10mS = 1

μSecond x (256 - Preload Value) x 64

10mS/(1

μSecond x 64) = 256 - Preload Value

Preload Value = 256 - [10mS/(1

μSecond x 64)]

Preload Value = 99.75 rounded up becomes 100

Therefore, to produce a 10 mS overflow period, using the internal instruction clock with a 4 MHz internal oscillator and a TMR0 prescaler value of 1:64 requires that TMR0 be preloaded with a value of 100.

Delay_10mS()

END

YES

Preload TMR0 register with 100

Clear the TMR0 overflow flag

(T0IF)

T0IF = 0?

Finally, TMR0 is a writable register. Meaning that a value can be added to the register to offset the number of counts it takes for the overflow to occur. Equation 3-3 demon- strates how to calculate the value to preload the TMR0 register with to create a 10mS overflow period.

EQUATION 3-3: CALCULATING A TMR0 PRELOAD VALUE TO GENERATE A

10MS OVERFLOW PERIO D

The software flowchart to implement a 10mS delay is shown in Figure 3-13.

FIGURE 3-13: DELAY_10MS() USING TIMER0

The maximum overflow period that can be achieved using Timer0 only utilizes a 1:256 prescaler is as shown in Equation 3-4.

General Purpose Input/Output Labs

TMR0 Overflow Period = (4/FOSC) x 256 x prescaler

using a maximum prescaler setting of 1:256 and the 4MHz internal oscillator

TMR0 Overflow Period = 1 μS x 256 x 256 = 65.5mS

Delay_1S()

END

YES

counter variable value determined as follows: 1 second/65.5mS = 15.25 or rounded down to 15

Create an 8-bit variable counter and

initialize to 0

Clear the TMR0 register

Clear the TMR0 overflow flag

(T0IF)

T0IF = 0?

counter < or = 15?

Increment counter value by 1

YES

EQUATION 3-4: MAXIMUM TMR0 OVERFLOW PERIOD

Therefore, to implement delays greater than 65.5mS, a counter variable is implemented as shown in the flowchart of Figure 3-14 for a 1 second delay.

FIGURE 3-14: DELAY_1S() USING TIMER0

PICDEMTM Lab Development Board User’s Gu ide

/*---------------------------------------------------------

Subroutine: Delay_1S Parameters: none Returns:nothing Synopsis:Creates a 1S delay when called

---------------------------------------------------------*/ void Delay_1S(void) {

//Create an 8-bit variable called counter //and initialize it to 0 unsigned char counter = 0;

while(counter <= 15) { //Make sure the T0IF is cleared T0IF = 0;

//Clear the TMR0 register TMR0 = 0; //Sit here and wait for Timer0 to overflow

while (T0IF == 0); ++counter;

}

The Initialize() now configures the PIC16F690 peripherals as follows:

•PORTC

- Set all bits in PORTC high

- Make all PORTC pins digital output

•Timer0

- Use the internal instruction clock (F

- Increment TMR0 register on low-to-high transition of F

- Assign the prescaler to Timer0 and configure to increment on every 256th transition of F

OSC/4

3.3.6.3 PROCEDURE

Using the firmware developed in the previous lab, make the following changes:

1. Copy/paste the code in Example 3-8 at the top of the main firmware source file under the heading labeled:

/**SUPPORT ROUTINES**********************************/

EXAMPLE 3-8: DELAY_1S() CODE FOR LAB 3

OSC/4) as the TMR0 register clock source

OSC/4

2. Copy/paste the code in Example 3-9 into the Initialize() over the code from the previous lab.

General Purpose Input/Output Labs

//Set all PORTC bits HIGH (to a known state)

PORTC = 0b11111111;

//Configure Timer0 as follows: T0CS = 0; //Use the internal instruction clock

//FOSC/4 as the clock source

T0SE = 0;//Increment TMR0 on low-to-high

//FOSC/4 transition

PSA = 0;//Assign the prescaler to

//Timer0

//Configure Timer0 prescaler to increment //TMR0 every 256 FOSC/4 clock transitions PS0 = 1; PS1 = 1; PS2 = 1;

Delay_1S(); //Call the 1 second delay

EXAMPLE 3-9: INITIALIZE() CODE FOR LAB 3

3. Finally, copy/paste the code in Example 3-10 into the Timing() over the code

from the previous lab

EXAMPLE 3-10: TIMING() CODE FOR LAB 3

4. The remaining code from the previous lab remains the same. Compile the proj-

ect. There should be no errors.

3.3.6.4 TESTING THE APPLICATION

Program the PIC16F690. The application should behave exactly as it did in the previous lab. Using an oscilloscope to test individual PORTC pin level transitions would be useful to analyze the accuracy of the delay.

The solution for this project is located in the C:\PICDEM_Lab\GPIO_Labs\GPIO_Lab3\solution directory.

Note: More in-depth tutorials on the Timer0 peripheral are covered in “Timers:

Timer0 Tutorial (Part 1)” (5162a.pdf) and “Timers: Timer0 Tutorial (Part 2)” (51702a.pdf) files included on the PICDEM™ Lab Development Kit CD.

PICDEMTM Lab Development Board User’s Gu ide

main()

Initialize()

Do_Outputs()

Loop Forever

Timing()

Decide()

Global Variables:

• 8-bit LED_Output

Decide()

LED_Output = 0b10000000

LED_Output = 0b00000000

END

Shift contents of LED_Output

variable left by 1 bit position

YES

LED_Output = 0b00000001

LED_Output variable initialize to 0b00000001 in Initialize()

3.3.7 Lab 4: Rotate LEDs

3.3.7.1 OVERVIEW

This lab shifts a high bit in the PORTC register from right-to-left each time through the software loop sequentially lighting the LEDs connected to the PORTC pins in 1 second intervals as dictated by the Timing(). This lab adds some new functional blocks to the main() software control loop as shown in Figure 3-15.

FIGURE 3-15: MAIN() SOFTWARE CONTROL LOOP FLOWCHART FOR

LAB 4

The addition of an 8-bit global variable (can be manipulated by any function) called LED_Output is used. This variable will be acted upon by the new Decide() by shifting a high bit in LED_Output from right-to-left each time this function is called. The flowchart for the Decide() is shown in Figure 3-16.

FIGURE 3-16: DECIDE() FLOWCHART FOR LAB 4

General Purpose Input/Output Labs

Do_Outputs()

assigns

LED_Output to

PORTC

LED_Output variable

10000000

PORTC

Do_Outputs()

assigns

LED_Output to

PORTC

01000000

LED_Output variable

PORTC

Decide() shifts contents of

LED_Output Left by 1 bit position

Corresponding LED lights

First time through main():

Next time through main():

Initialize() determines initial

contents of LED_Output

The Decide() first checks the current value in LED_Output for two specific conditions:

• Is the Most Significant bit ‘1’? This means that on the next shift, the contents will

be all ‘0’s.

• Is the value currently a ‘0’?

If either condition exists, the function re-initializes LED_Output to set the Least Significant bit. Otherwise, there will be a period when none of the LEDs are lit.

The shift is implemented in code as follows:

LED_Output <<= 1;

This translates to: “LED_Output is equal to the current contents of LED_Output shifted to the left by 1 bit position”

Conversely, to shift the bit to the right the code would be as follows:

LED_Output >>= 1;

The Do_Outputs() will then assign the contents of the LED_Output variable to the PORTC register and whichever bit is high will light the connected LED. (See Figure 3-17.)

FIGURE 3-17: RESULTS OF DO_OUTPUT()

The Initialize() now configures the PIC16F690 peripherals as follows:

•PORTC

- Initialize PORTC so that the 7 Most Significant bits are ‘0’ and the Least Significant bit is ‘1’

- Make all PORTC pins digital output

•Timer0

- Use the internal instruction clock (F

- Increment TMR0 register on low-to-high transition of F

- Assign the prescaler to Timer0 and configure to increment on every 256th

• Initialize the LED_Output variable to ‘0’

transition of F

OSC/4

OSC/4) as the TMR0 register clock source

OSC/4

PICDEMTM Lab Development Board User’s Gu ide

unsigned char LED_Output;//Variable used to set/clear PORTC bits

//Clear PORTC to a known state PORTC = 0b00000001;

//Configure PORTC pins as all output //i.e. 1 = Input, 0 = Output TRISC0 = 0;//Associated with RC0 TRISC1 = 0;//Associated with RC1 TRISC2 = 0;//Associated with RC2 TRISC3 = 0;//Associated with RC3 TRISC4 = 0;//Associated with RC4 TRISC5 = 0;//Associated with RC5 TRISC6 = 0;//Associated with RC6 TRISC7 = 0;//Associated with RC7

//Configure Timer0 as follows: T0CS = 0; //Use the internal instruction clock

//FOSC/4 as the clock source

T0SE = 0;//Increment TMR0 on low-to-high

//FOSC/4 transition

PSA = 0;//Assign the prescaler to

//Timer0

//Configure Timer0 prescaler to increment //TMR0 every 256 FOSC/4 clock transitions PS0 = 1; PS1 = 1; PS2 = 1; //Initialize LED_Output to all zeros LED_Output = 0b00000000;

3.3.7.2 PROCEDURE

Using the code developed in the previous lab, make the following changes:

1. The LED_Output variable will need to be declared before it can be used.

Copy/paste the code in Example 3-11 to the beginning of the source file under the section marked:

//-----------------DATA MEMORY------------------------

EXAMPLE 3-11: LED_OUTPUT VARIABLE DECLARATION FOR LAB 4

2. Copy/paste the code in Example 3-12 over the Initialize() code from the

previous lab.

EXAMPLE 3-12: INITIALIZE() CODE FOR LAB 4

General Purpose Input/Output Labs

//First check if LED_Output variable has most significant bit //set to 1 or if LED_Output variable is all 0's. //If so, re initialize the LED_Output variable so that the //least significant bit is set to 1 and all other bits are //cleared to 0

if((LED_Output == 0b10000000) || (LED_Output == 0b00000000))

LED_Output = 0b00000001;

//If neither of these conditions are true, simply shift //the LED_Output variable's contents to the Left by 1 bit //position

else LED_Output <<=1;

//Assign the manipulated contents of the //LED_Output variable to the PORTC register

PORTC = LED_Output;

Initialize(); //Initialize the relevant registers

while(1) {

Decide(); //Make any decisions

Do_Outputs(); //Perform any outputs

Timing();//Sets execution rate of the

//Software Control Loop

}

Changes from the previous lab include PORTC initialization so that all bits are ‘0’ except for the Least Significant bit (LSb) and the initialization of the LED_Output variable.

3. Copy/paste the code in Example 3-13 into the Decide() section labeled:

//ADD DECISION CODE HERE

EXAMPLE 3-13: DECIDE()CODE FOR LAB 4

4. Copy/paste the code in Example 3-14 over the Do_Outputs() code from the

previous lab.

EXAMPLE 3-14: DO_OUTPUTS() CODE FOR LAB 4

This code simply assigns the contents of the LED_Output variable to the PORTC register.

5. Copy/paste the code in Example 3-15 over the main() code from the previous lab to incorporate the Decide().

EXAMPLE 3-15: MAIN() CODE FOR LAB 4

Compile the project. There should be no errors.

PICDEMTM Lab Development Board User’s Gu ide

3.3.7.3 TESTING THE APPLICATION

Program the PIC16F690. The LEDs connected to the individual PORTC pins should now all flash on/off sequentially from right-to-left in 1 second intervals.

The solution for this project is located in the C:\PICDEM_Lab\GPIO_Labs\GPIO_Lab4\solution directory.

3.4 GPIO INPUT LABS

3.4.1 Reference Documentation

PIC16F690 Data Sheet

• Section 2: Memory Organization

• Section 4: I/O Ports

• Section 5: Timer0 Module

3.4.2 Equipment Required for GPIO Input Labs

To complete the labs in this section, the following components are required:

1. 1 – push button

2. 8 – Light Emitting Diodes

3. 1 – 10 K

4. 8 – 470Ω resistors

5. PIC16F690 populating socket U2

6. Assorted jumper wires

3.4.3 PICDEM Lab Development Board Setup for GPIO Input Labs

The GPIO input labs will require that the PICDEM Lab Development Board be configured as shown in Figure 3-12 using the components listed in the previous section.

General Purpose Input/Output Labs

1 2 3 4 5 6 7 8 9

20 19 18 17 16 15 14 13 12 11

RC0 RC1 RC2

RC3

RC4

RC5

RC6

RC7

J9J8

R8 470Ω

R4 470Ω

R7 470Ω

R6 470Ω

R5 470Ω

R3 470Ω

R2 470Ω

R1 470Ω

LED8 LED7 LED6 LED4 LED3 LED2 LED1LED5

R9 10KΩ

SW1

RA2

FIGURE 3-18: PICDEM LAB SCHEMATIC FOR GPIO INPUT LABS

The only change from the previous section is the inclusion of a push button connected to RA2 with associated pull-up resistor.

3.4.4 Lab 5: Adding a Push Button

3.4.4.1 NEW REGISTERS USED IN THIS LAB

To configure the peripherals used in this lab, the following registers are used:

1. PORTA Register: PORTA (Register 4-1 in Section 4 of the PIC16F690 Data Sheet)

- 8-bit bidirectional port

2. PORTA Tri-State Register: TRISA (Register 4-2 in Section 4 of the PIC16F690 Data Sheet)

- Configures corresponding bits in PORTA as either input or output

3.4.4.2 OVERVIEW

This lab expands upon Lab 4 by adding a push button interface to change the direction of the sequential shift in the PORTC register.

Mechanical switches play an important and extensive role in practically every computer, microprocessor and microcontroller application. Mechanical switches are inexpensive, simple and reliable. However, switches can be very noisy electrically. The apparent noise is caused by the closing and opening action that seldom results in a clean electrical transition. The connection makes and breaks several, perhaps even hundreds, of times before the final switch state settles. The problem is known as switch bounce. Some of the intermittent activity is due to the switch contacts actually bouncing off each other. Also, switch contacts are not perfectly smooth. As the contacts move against each other, the imperfections and impurities on the surfaces cause the electrical connection to be interrupted. The result is switch bounce. The consequences

PICDEMTM Lab Development Board User’s Gu ide

main()

Initialize()

Do_Outputs()

Loop Forever

Timing()

Decide()

Global Variables:

• 8-bit variable LED_Output will be used to light the LEDs connected to PORTC

• 1-bit variable direction used to determine the direction of the s e que ntial LED flashing

0 = shift PORTC bits right-to-left 1 = shift PORTC bits left-to-right

Get_Inputs()

of uncorrected switch bounce can range from being just annoying to catastrophic. The classic solution involves filtering, such as through a resistor-capacitor circuit, or through resettable shift registers. These methods are still effective but they involve additional cost in material, installation and board real estate. Debouncing in software eliminates these additional costs.

One of the simplest ways to switch debounce is to sample the switch until the signal is stable or continue to sample the signal until no more bounces are detected. How long to continue sampling requires some investigation. However, 5 mS is usually adequate, while still reacting fast enough that the user won't notice it.

The software flowchart for this application is shown in Figure 3-19.

FIGURE 3-19: MAIN() SOFTWARE CONTROL LOOP FLOWCHART FOR

LAB 5

The Initialize() now configures the following:

•PORTC

- Configure PORTC pins as per the previous labs

•PORTA

- Clear PORTA register.

- Configure RA2 as a digital input pin

• Timer0 will be configured to implement the 5mS delay as follows:

- Use the internal instruction clock F

- Increment TMR0 on the low-to-high transition of F

- Assign the prescaler to TMR0 and configure 1:64.

• Initialize the LED_Output variable to ‘0’

• Initialize the direction bit variable to ‘0’

- This is a global variable that will be manipulated by the new Get_Inputs()

(see Registers 4-1 and 4-2 in Section 4.1 of the PIC16F690 Data Sheet).

OSC/4 as the TMR0 clock source.

OSC/4.

and used to determine PORTC shift direction by the Decide().

General Purpose Input/Output Labs

Get_Inputs()

RA0 = 0

END

Contents of direction

remain unchanged

YES

Delay_5mS()

RA0 = 0

Toggle contents of

direction

YES

Debounces signal on RA2

A new function called Get_Inputs() is used to check the RA2 pin voltage. Referring to Figure 3-12, the RA2 pin connected to the push button (SW1) is pulled to V a 10 KΩ

resistor. This pull-up resistor eliminates noise on the pin that could trigger

“false” push button presses. The second terminal of the push button is connected to V

SS. In this way, when a user presses the push button the voltage present on RA2 will

transition from V

(high or ‘1’) to VSS (low or ‘0’). The software flowchart for the

Get_Inputs() is shown in Figure 3-20.

FIGURE 3-20: GET_INPUTS() SOFTWARE FLOWCHART FOR LAB 5

DD using

Referring to the flowchart in Figure 3-20, the Get_Inputs() first checks the voltage level on the RA2 pin. If the voltage is logic low (= 0 or V

SS), a 5mS delay is implemented

using a new support routine called Delay_5mS() to allow any switch bouncing to settle. The Delay_5mS() is based off of the Timer0 peripheral as discussed in Lab 3. The software flowchart for Delay_5mS() is shown in Figure 3-21.

PICDEMTM Lab Development Board User’s Gu ide

Delay_5mS()

T0IF = 1

(i.e., TMR0 overflow)

END

Clear the Timer0 overflow

flag (T0IF)

YES

Preload the Timer0 result register (TMR0) with 100

Timer0 configured in the Initialize() as fol- lows:

• Using the internal F

OSC/4 (4MHz/4) clock

source

• TMR0 increments on low-to-high transition

of F

OSC/4

• Prescaler configured for 1:32

Desired Timer0 Overflow Rate = (4/F

OSC) x number of counts to overflow x prescaler

5mS = 1μSeconds x (256 – TMR 0 preload value) x 32 TMR0 preload value = 256 – 5mS = 99.75 rounded to 100

1μSeconds x 32

TMR0 preload valu e det er m ined as follows:

FIGURE 3-21: DELAY_5MS() SOFTWARE FLOWCHART FOR LAB 5

The RA2 pin voltage is then checked again. If still low, a push button press is indicated and the direction bit variable is toggled. Otherwise, the direction value stays the same.

The Decide() then uses the current direction value to determine which direction to shift the contents of the LED_Output global variable. The Decide() software flowchart is shown in Figure 3-22.

General Purpose Input/Output Labs

Decide()

direction = 0

END

LED_Output =

0b00000001

YES

Shift contents of

LED_Output left

by 1 bit position

YES

LED_Output = 0b10000000

LED_Output = 0b00000000

YES

LED_Output = 0b10000000

Shift contents of

LED_Output right

by 1 bit position

LED_Output = 0b00000001

LED_Output = 0b00000000

unsigned char LED_Output;//Variable used to set/clear PORTC bits

bit direction;//Variable to select direction of shifting LEDs

FIGURE 3-22: DECIDE() SOFTWARE FLOWCHART FOR LAB 5

Similar to the previous lab, Decide() checks the LED_Output variable value before executing the shift to ensure that the variable is not all 0’s or that the Most Significant bit, for a left shift, or Least Significant bit, for a right shift, are not ‘1’, indicating that the shift that follows will fill the LED_Output variable with 0’s.

The Do_Outputs() simply assigns the contents of the LED_Output variable to the PORTC register lighting the connected LEDs accordingly.

3.4.4.3 PROCEDURE

Using the firmware developed in the previous lab, make the following changes:

Copy/paste the code in Example 3-16 into the top of the firmware source template under the section marked:

//--------------------DATA MEMORY----------------------

EXAMPLE 3-16: VARIABLE DECLARATIONS FOR LAB 5

PICDEMTM Lab Development Board User’s Gu ide

/*---------------------------------------------------------

Subroutine: Delay_5mS Parameters: none Returns:nothing Synopsis:Creates a 5mS delay when called

---------------------------------------------------------*/ void Delay_5mS(void) {

//Make sure the T0IF is cleared T0IF = 0;

//preload the TMR0 register TMR0 = 100;

//Sit here and wait for Timer0 to overflow while (T0IF == 0);

}

1. Copy/paste the function code in Example 3-17 into the top of the firmware source template under the section marked:

/**SUPPORT ROUTINES*************************************

EXAMPLE 3-17: DELAY_5MS() CODE FOR LAB 5

2. Copy/paste the code in Example 3-18 into the Initialize() over the code from the previous lab.

General Purpose Input/Output Labs

//Clear PORTC to a known state //Set the least significant bit to 1 so that it can be //shifted through PORTC = 0b00000001;

//Clear the PORTA register to a known state PORTA = 0b00000000;

//Configure PORTA bit RA0 as Digital input ANS2 = 0; TRISA2 = 1;

//Configure Timer0 to overflow every 5mS T0CS = 0; //Select FOSC/4 as Timer0 clock source T0SE = 0; //Increment TMR0 on rising clock edge PSA = 0; //Assign prescaler to Timer0 //Select a 1:32 prescaler PS0 = 0; PS1 = 0; PS2 = 1;

//Initialize the direction flag to shift bits from //right-to-left //(i.e. 0 = Shift PORTC bits from right-to-left // 1 = Shift PORTC bits from left-to-right direction = 0;

//Initialize LED_Output to all zeros LED_Output = 0b00000000;

EXAMPLE 3-18: INITIALIZE() FOR GPIO LAB 5

PICDEMTM Lab Development Board User’s Gu ide

//Check for a push button press (i.e. RA2 = 0) if (RA2 == 0) {

Delay_5mS(); //Delay to debounce

//Check if push button is still pressed if(RA2 == 0) direction ^= 1; //If so, toggle the

//direction bit } //Otherwise keep direction the same as it was else direction = direction;

if(direction == 0) { //First check if LED_Output variable has most //significant bit set to 1 or if LED_Output variable is //all 0's. //If so, re initialize the LED_Output variable so that //the most significant bit is set to 1 and all other //bits are 0

if((LED_Output == 0b00000001) || (LED_Output ==

0b00000000)) LED_Output = 0b10000000;

//If neither of these conditions are true, simply shift //the LED_Output variable's contents to the Left by 1 //bit position

else LED_Output >>=1;

}

else { //First check if LED_Output variable has the least //significant bit set //to 1 or if LED_Output variable is all 0's. //If so, re initialize the LED_Output variable so that //the least significant bit is set to 1 and all other //bits are 0

if((LED_Output == 0b10000000) || (LED_Output ==

0b00000000)) LED_Output = 0b00000001;

//If neither of these conditions are true, simply shift //the LED_Output variable's contents to the Right by 1 //bit position

else LED_Output <<=1;

}

3. Copy/paste the code in Example 3-19 into the Get_Inputs() at the section

labeled:

//ADD GET_INPUTS CODE HERE

EXAMPLE 3-19: GET_INPUTS() CODE FOR GPIO LAB 5

4. Copy/paste the code in Example 3-20 into the Decide() over the code from the

previous lab.

EXAMPLE 3-20: DECIDE() CODE FOR GPIO LAB 5

General Purpose Input/Output Labs

unsigned int delay_var = 9997;

//Keep looping until the delay_var is // equal to zero (should take 10mS) while(--delay_var);

Initialize(); //Initialize the relevant registers

while(1) {

Get_Inputs();//Evaluate inputs Decide();//Make any decisions Do_Outputs(); //Perform any outputs Timing();//Sets execution rate of the

//Software Control Loop

}

5. The Do_Outputs() code from the previous lab stays the same.

6. Copy/paste the code in Example 3-21 into the Timing() over the code from the

previous lab.

EXAMPLE 3-21: TIMING() CODE FOR GPIO LAB 5

Note: This lab now utilizes a 10 mS delay to time the software control loop.

7. Copy/paste the code in Example 3-22 over the main() code from the previous

lab.

EXAMPLE 3-22: MAIN() CODE FOR LAB 5

8. Compile the project, there should be no errors.

3.4.4.4 TESTING THE APPLICATION

Program the PIC16F690. Once programmed, the LEDs connected to PORTC should sequentially light from left-to-right in 10 mS intervals. When the push button is pressed, the LEDs should change directions and sequentially light from right-to-left. Continuously pressing the push button will change the direction each time.

It should be noted that the push button press inconsistently changes the direction of sequential flashing. The problem here is that the firmware performs a technique called "Polling" to check the state of the RA0 pin that connects to the push button. Therefore, the state of RA0 is checked only once each time through the software control loop when the Get_Inputs() is called. This polling is subject to the timing of the software control loop and will lead to push button presses being missed. If the Timing() remained at the 1 second delay as implemented in the previous lab, this would have made matters worse. The next labs will remedy these issues through the use of interrupts.

The solution for this project is located in the C:\PICDEM_Lab\GPIO_Labs\GPIO_Lab5\solution directory.

PICDEMTM Lab Development Board User’s Gu ide

3.4.5 Lab 6: Push Button Interrupt

3.4.5.1 NEW REGISTERS USED IN THIS LAB

To configure the peripherals used in this lab, the following registers are used:

1. OPTION Register: OPTION (Register 2-2 in Section 2 of the PIC16F690 Data Sheet)

- Selects the edge transition on RA2/INT that will trigger an interrupt.

2. Interrupt Control Register: INTCON (Register 2-3 in Section 2 of the PIC16F690 Data Sheet)

- Enable interrupt functionality on the PIC16F690.

- Enables the RA2/INT external interrupt.

- Contains a flag that indicates the external interrupt has occurred.

3.4.5.2 OVERVIEW

This lab expands upon Lab 5 by adding an interrupt that will occur each time the push button connected to the RA2 pin is pressed.

As mentioned, polling a bit is heavily reliant on a number of factors such as the size of the firmware and the timing of the software control loop. Polling does have its uses. However, there may be times when an event, such as pressing a push button, requires immediate attention. This is where the interrupt comes in. As the name implies, an interrupt acts as a sort of alarm. When the Central Processing Unit receives an interrupt, it immediately stops what it is doing, saves where in the code it was before the interrupt, performs code or firmware defined by the user in the event of an interrupt called an Interrupt Service Routine (ISR), and then returns to the previous task it was performing prior to the interrupt.

So, why not use interrupts all the time? The answer is mainly cost. In order to implement an interrupt for a specific function, the user may need to purchase a microcontroller with a peripheral that accommodates the interrupt. This increases the cost of the application. In some cases, polling a bit may be the way to go. Other cases may require the interrupt thereby justifying the added cost of a particular peripheral.

The RA2 pin associated with the PORTA register features an external edge-triggered interrupt capability (note the INT designation on the PIC16F690 Pin Diagram in Table 5 of the data sheet). The interrupt is configurable to occur on either the rising-edge (i.e., signal on RA2 pin transitions from low-to-high) or the falling-edge (i.e., signal on RA2 pin transitions from high-to-low) of the voltage on the RA2 pin. If the selected edge transition is detected on RA2, the CPU then services the interrupt before returning to the code it was executing prior to the interrupt. Referring again to Figure 3-12, the push button connected to the RA2 pin is pulled high when not pressed. Therefore, the interrupt will be configured to trigger on the high-to-low transition indicating a push button press.

The INTCON register contains the enable (INTE) and flag (INTF) bits for the RA2 external interrupt. These bits indicate to firmware the condition that caused an interrupt to occur. The other bits and accompanying registers are used for other peripheral features on the microcontroller. The Global Interrupt Enable bit (GIE) is a sort of master switch that allows interrupts, if individually enabled, to be used by the microcontroller.

The OPTION register features the Interrupt Edge Select (INTEDG) bit that will be used to indicate the edge transition that will trigger an interrupt.

The software flowchart for this lab is shown in Figure 3-23.

General Purpose Input/Output Labs

main()

Initialize()

Do_Outputs()

Loop Forever

Timing()

Decide()

Global Variables:

• 8-bit variable LED_Output will be used to light the LEDs connected to PORTC

• 1-bit variable direction used to determine the direction of the sequential LED flashing

0 = shift PORTC bits right-to-left 1 = shift PORTC bits left-to-right

PB_PressISR()

INTE and INTF

bits set

RETURN

Clear INTF flag

YES

RA2 pin = 0

direction = direction

Delay for 5mS

YES

RA2 pin = 0

To gg l e direction

YES

FIGURE 3-23: MAIN() SOFTWARE CONTROL LOOP FLOWCHART FOR

GPIO LAB 6

Note the removal of the Get_Inputs() from the previous lab. This code will now be handled by an Interrupt Service Routine (ISR) whenever the push button is pressed. The PB_PressISR() flowchart is shown in Figure 3-24.

FIGURE 3-24: PB_PRESSISR() FOR LAB 6 SHOWING SWITCH DEBOUNCE

PICDEMTM Lab Development Board User’s Gu ide

/*---------------------------------------------------------

Subroutine: Interrupt Service Routine Parameters: none Returns:nothing Synopsis:Execute this code on any interrupt

---------------------------------------------------------*/

void interrupt PB_PressISR(void) {

//Check to see if the interrupt was caused by //the external interrupt on RA2 //If so, clear the external interrupt flag //to allow subsequent interrupts to be detected if(INTE && INTF) INTF = 0;

//Check to see if the RA2 pin is 0 //(i.e. push button pressed) if(RA2 == 0) {

//If RA2 is 0 delay for 5mS to filter //any switch bounce Delay_5mS();

//Check to see if RA2 is still 0 //If so, toggle the direction bit if(RA2 == 0) direction ^= 1;

}

//If RA2 is not 0, keep direction value //the same as it was else direction = direction;

}

Referring to the flowchart in Figure 3-24, the PB_PressISR() replaces the Get_Inputs() used in Lab 4 with a few additions. At the beginning of the ISR, the

INTE and INTF bits are first checked to ensure that the RA2/INT external interrupt is indeed enabled and that the flag is set indicating that an RA2/INT external interrupt has occurred. Determining the source of an interrupt becomes especially important if multiple peripherals are configured to cause an interrupt. The ISR then clears the RA2/INT external interrupt flag so that subsequent interrupts will be registered. The ISR then performs the RA2 check along with the debounce routine that was discussed in the previous lab.

3.4.5.3 PROCEDURE

Using the firmware developed in the previous lab, make the following changes:

1. Copy/paste the Interrupt Service Routine in Figure 3-23 at the top of the firmware source file under the section labeled:

/**INTERRUPT CODE***************************************/

EXAMPLE 3-23: PB_PRESSISR() CODE FOR GPIO LAB 6

General Purpose Input/Output Labs

Note: To indicate a function that should be used whenever an interrupt occurs, the

interrupt function qualifier is needed. This qualifier is specific to the HI-TECH C

2. Copy/paste the code in Example 3-24 into the Initialize() over the code

from the previous lab.

Compiler.

PICDEMTM Lab Development Board User’s Gu ide

//Clear PORTC to a known state //Set the least significant bit to 1 so that it can be //shifted through

PORTC = 0b00000001;

//Clear the PORTA register to a known state

PORTA = 0b00000000;

//Configure PORTC's ANALOG/DIGITAL pins as all Digital

ANS4 = 0;//Associated with RC0 ANS5 = 0;//Associated with RC1 ANS6 = 0;//Associated with RC2 ANS7 = 0;//Associated with RC3 ANS8 = 0;//Associated with RC6

ANS9 = 0;//Associated with RC7 //Configure PORTC pins as all output //i.e. 1 = Input, 0 = Output

TRISC0 = 0;//Associated with RC0

TRISC1 = 0;//Associated with RC1

TRISC2 = 0;//Associated with RC2

TRISC3 = 0;//Associated with RC3

TRISC4 = 0;//Associated with RC4

TRISC5 = 0;//Associated with RC5

TRISC6 = 0;//Associated with RC6

TRISC7 = 0;//Associated with RC7

//Configure PORTA bit RA0 as Digital input

ANS2 = 0;

TRISA2 = 1;

//Configure Timer0 to overflow every 5mS

T0CS = 0; //Select FOSC/4 as Timer0 clock source

T0SE = 0; //Increment TMR0 on rising clock edge

PSA = 0; //Assign prescaler to Timer0 //Select a 1:32 prescaler

PS0 = 0;

PS1 = 0;

PS2 = 1;

//Initialize the direction flag to shift bits from //right-to-left //(i.e. 0 = Shift PORTC bits from right-to-left // 1 = Shift PORTC bits from left-to-right

direction = 0; //Initialize LED_Output to all zeros

LED_Output = 0b00000000;

//Configure for external interrupts on RA2

INTEDG = 0; //Interrupt to occur on High-to-LOW

//transition of RA2 voltage INTE = 1; //Enable the external interrupt INTF = 0; //Clear the external interrupt flag GIE = 1;//Enable interrupt capability on the

//PIC16F690 ***ALWAYS DONE LAST*****

EXAMPLE 3-24: INITIALIZE() CODE FOR GPIO LAB 6

It should be noted that the Global Interrupt Enable bit (GIE) is set last in the

Example 3-24. This ensures that interrupts will not occur during the Initialize(),

having adverse consequences on code operation.

General Purpose Input/Output Labs

Initialize(); //Initialize the relevant registers

while(1) {

Decide();//Make any decisions Do_Outputs(); //Perform any outputs Timing();//Sets execution rate of the

//Software Control Loop

}

3. Copy/paste the code in Example 3-25 into the main() over the code from the previous lab to remove the Get_Inputs().

EXAMPLE 3-25: MAIN() CODE FOR GPIO LAB 6

4. The remaining code remains unchanged from the previous lab. Compile the project. There should be no errors.

3.4.5.4 TESTING THE APPLICATION

Program the PIC16F690. The application should behave as it did in the previous lab. Only this time, the change in LED flashing direction should now be more responsive to push button presses due to the interrupt added.

The solution for this project is located in the C:\PICDEM_Lab\GPIO_Labs\GPIO_Lab6\solution directory.

3.4.6 Lab 7: Push Button Interrupt-on-Change

3.4.6.1 NEW REGISTERS USED IN THIS LAB

To configure the peripherals used in this lab, the following registers are used:

1. Interrupt-on-Change PORTA Register: IOCA (Register 4-6 in Section 4 of the PIC16F690 Data Sheet).

- Configures PORTA associated pins that will generate an interrupt when a change in voltage level is detected.

2. Interrupt Control Register: INTCON (Register 2-3 in Section 2 of the PIC16F690 Data Sheet)

- Enable interrupt functionality on the PIC16F690.

- Enables PORTA/PORTB change interrupts.

- Contains a flag that indicates that a PORTA or PORTB change interrupt has occurred.

3.4.6.2 OVERVIEW

This lab adds a different kind of interrupt associated with the General Purpose Input/Output peripheral called interrupt-on-change. Rather than simply interrupting the CPU on a single edge transition on the RA2 pin, an interrupt will now occur on any edge transition. Therefore, when the push button is pressed and/or released, an interrupt will occur. This lab will use these concepts to shift the flashing LEDs from left-to-right while the push button is pressed and from right-to-left when the push button is released.

Each PORTA and PORTB pin is individually configurable as an interrupt-on-change pin. Control bits in the Interrupt-on-Change PORTA register (IOCA) enable or disable the interrupt function for each pin.

PICDEMTM Lab Development Board User’s Gu ide

pb_pressISR()

RABIE and RABIF

bits set

RETURN

Clear RABIF flag

YES

RA2 pin = 0

direction = 1

Delay for 5mS

RA2 pin = 0

RA2 pin = 1

Delay for 5mS

RA2 pin = 1

direction = 1

Read PORTA

YES

The INTCON register is needed as well to implement the interrupt-on-change feature. Again the GIE bit needs to be set to enable any interrupts used on the microcontroller. To configure for an interrupt-on-change, the PORTA/PORTB Change Interrupt Enable bit (RABIE) must be set along with the individual enable bits in the IOCA register. On an interrupt-on-change for configured pins, the PORTA/PORTB Change Interrupt Flag bit (RABIF) will be set. To detect a logic change on a port pin, the firmware needs to know what has changed. Therefore, PORTA must be read before an interrupt-on-change can occur. Reading PORTA retains, or latches, the current value on the RA2 pin for later reference. In the event that the signal on the RA2 pin changes and a mismatch with the reference value occurs, an interrupt will result.

The main() software flowchart for this lab remains the same as that in Figure 3-24 of the previous lab. The Interrupt Service Routine changes since it now must determine whether the interrupt occurred due to a high-to-low or low-to-high transition on pin RA2. The ISR flowchart is shown in Figure 3-25.

FIGURE 3-25: PB_PRESSISR FLOWCHART FOR LAB 7

General Purpose Input/Output Labs

The PB_PressISR() now checks to see if the voltage level on RA2 has changed state from a 1-to-0 or from 0-to-1. Each condition will change the direction that the LEDs flash sequentially. Note that the direction bit toggle used in previous labs has been replaced by assigning either a ‘1’ for the left-to-right direction or ‘0’ for the right-to-left direction. As discussed earlier, the PORTA register must be read before the first interrupt can occur and at the end of each subsequent ISR execution to ensure that the microcontroller has an up-to-date reference to measure the current state of the RA2 pin.

The Initialize() for this lab configures the peripherals and interrupts as follows:

•PORTC

-Clears PORTC

- Configures all pins as digital output

•PORTA

-Clears PORTA

- Configures RA2 as a digital input

•Timer0

- Uses the F

- Increment TMR0 on rising F

- Use Prescaler at 1:32

• Global Variables

- Initialize direction to ‘0’

- Initialize LED_Output to ‘0’

• Interrupt

- Enable RA2 Interrupt-on-Change

- Enable change interrupts in INTCON by setting the RABIE bit

- Clear the RABIF change interrupt flag in INTCON

- Enable Global Interrupts by setting GIE

- Read PORTA to latch current value on RA2 for reference

OSC/4 as clock source

OSC/4 clock edge

3.4.6.3 PROCEDURE

Using the firmware developed in the previous lab, make the following changes:

1. Copy/paste the code in Example 3-26 into the PB_PressISR() over the code

from the previous lab.

PICDEMTM Lab Development Board User’s Gu ide

//First, check if the interrupt occurred as a result of an //RA2 change interrupt. If so, clear the RABIF flag so //that subsequent interrupts can occur if(RABIE && RABIF) RABIF = 0; //Check the push button connected to RA0 pin. If 0, then a //push button press is indicated

if(RA2 == 0) {

//Delay for 5mS to filter switch bounce Delay_5mS();

//if RA2 is still 0 then change the direction flag

if (RA2 == 0) direction = 1;

}

//Check the push button connected to RA0 pin. If 1, then a //push button release is indicated

if(RA2 == 1) {

//Delay for 5mS to filter switch bounce Delay_5mS();

//if RA2 is still 1 then change the direction flag

if (RA2 == 1) direction = 0;

}

//Otherwise, keep the direction bit the same as it was

else direction = direction;

//Read PORTA to latch RA2 value for the next interrupt

PORTA = PORTA;

EXAMPLE 3-26: PB_PRESSISR() CODE FOR GPIO LAB 7

2. Copy/paste the code in Example 3-27 into the Initialize() over the code

from the previous lab.

General Purpose Input/Output Labs

//Clear PORTC to a known state //Set the least significant bit to 1 so that it can be //shifted through

PORTC = 0b00000001;

//Clear the PORTA register to a known state

PORTA = 0b00000000;

//Configure PORTC's ANALOG/DIGITAL pins as all Digital

ANS4 = 0;//Associated with RC0 ANS5 = 0;//Associated with RC1 ANS6 = 0;//Associated with RC2 ANS7 = 0;//Associated with RC3 ANS8 = 0;//Associated with RC6 ANS9 = 0;//Associated with RC7

//Configure PORTC pins as all output //i.e. 1 = Input, 0 = Output

TRISC0 = 0;//Associated with RC0 TRISC1 = 0;//Associated with RC1 TRISC2 = 0;//Associated with RC2 TRISC3 = 0;//Associated with RC3 TRISC4 = 0;//Associated with RC4 TRISC5 = 0;//Associated with RC5 TRISC6 = 0;//Associated with RC6 TRISC7 = 0;//Associated with RC7

//Configure PORTA bit RA0 as Digital input

ANS2 = 0; TRISA2 = 1;

//Configure Timer0 to overflow every 5mS

T0CS = 0; //Select FOSC/4 as Timer0 clock source T0SE = 0; //Increment TMR0 on rising clock edge PSA = 0; //Assign prescaler to Timer0

//Select a 1:32 prescaler

PS0 = 0; PS1 = 0; PS2 = 1;

//Initialize the direction flag to shift bits from right-to-left //(i.e. 0 = Shift PORTC bits from right-to-left // 1 = Shift PORTC bits from left-to-right

direction = 0;

//Initialize LED_Output to all zeros

LED_Output = 0b00000000;

//Configure for RA2 Interrupt-On-Change

IOCA2 = 1; //Enable RA2 interrupt-on-change RABIE = 1; //Enable change interrupts RABIF = 0; //Clear the change interrupt flag GIE = 1;//Enable interrupt capability on the

//PIC16F690 ***ALWAYS DONE LAST*****

//Read PORTA to latch the current RA2 voltage level PORTA = PORTA;

EXAMPLE 3-27: INITIALIZE() CODE FOR GPIO LAB 7

PICDEMTM Lab Development Board User’s Gu ide

3. All remaining code from the previous lab is unchanged. Compile the project. There should be no errors.

3.4.6.4 TESTING THE APPLICATION

Program the PIC16F690. The LEDs connected to PORTC should now flash sequentially from left-to-right when the push button is released and flash from right-to-left when the push button is pressed.

The solution for this project is located in the C:\PICDEM_Lab\GPIO_Labs\GPIO_Lab7\solution directory.

3.4.7 Lab 8: Using Weak Pull-Ups

3.4.7.1 NEW REGISTERS USED IN THIS LAB

To configure the peripherals used in this lab, the following registers are used:

1. OPTION Register: OPTION (Register 2-2 in Section 2 of the PIC16F690 Data Sheet)

- Enables PORTA/PORTB weak pull-ups to be used on the PIC16F690.

2. PORTA Weak Pull-Up Register: WPUA (Register 4-5 in Section 4 of the PIC16F690 Data Sheet)

- Selects which PORTA pins will have weak pull-ups enabled.

3.4.7.2 OVERVIEW

This lab expands on the previous lab by adding weak pull-ups to remove the 10 K used previously to tie RA2 pin to VDD. Each of the PORTA pins (except RA3) and PORTB pins, has an individually configurable internal weak pull-up. Essentially, these weak pull-ups perform the same task as the resistor connected to the RA2 pin and push button as shown in Figure 3-12 only internal to the microcontroller. This feature can be used to decrease component counts in the circuit.

Clearing the PORTA/PORTB Pull-up Enable bit, RABPU enable weak pull-ups on any PORTA pin selected using the Weak Pull-Up PORTA register (WPUA).

The only change needed to the PICDEM Lab Development Board Schematic shown in Figure 3-18 is to remove the 10 KΩ resistor connected to both the push button and pin RA2.

The Initialize() is all that needs to be changed in firmware by adding the following configurations:

• Select RA2 to have a weak pull-up by setting the Weak Pull-Up Register bit

WPUA2 in the WPUA: PORTA Register.

• Enable the PORTA/PORTB Pull-up Enable bit (RABPU

by clearing it.

3.4.7.3 PROCEDURE

Using the firmware developed in the previous lab, make the following changes:

1. Copy/paste the code in Example 3-28 into the Initialize() over the code from the previous lab.

, in the OPTION register will

) in the OPTION register

General Purpose Input/Output Labs

//Clear PORTC to a known state //Set the least significant bit to 1 so that it can be //shifted through

PORTC = 0b00000001;

//Clear the PORTA register to a known state

PORTA = 0b00000000;

//Configure PORTC's ANALOG/DIGITAL pins as all Digital

ANS4 = 0;//Associated with RC0 ANS5 = 0;//Associated with RC1 ANS6 = 0;//Associated with RC2 ANS7 = 0;//Associated with RC3 ANS8 = 0;//Associated with RC6

ANS9 = 0;//Associated with RC7 //Configure PORTC pins as all output //i.e. 1 = Input, 0 = Output

TRISC0 = 0;//Associated with RC0

TRISC1 = 0;//Associated with RC1

TRISC2 = 0;//Associated with RC2

TRISC3 = 0;//Associated with RC3

TRISC4 = 0;//Associated with RC4

TRISC5 = 0;//Associated with RC5

TRISC6 = 0;//Associated with RC6

TRISC7 = 0;//Associated with RC7

//Configure PORTA bit RA0 as Digital input

ANS2 = 0;

TRISA2 = 1;

//Enable Weak Pull-ups on RA2

WPUA2 = 1;

RABPU = 0; //Enable PORTA/PORTB Pull-ups

//Configure Timer0 to overflow every 5mS

T0CS = 0; //Select FOSC/4 as Timer0 clock source

T0SE = 0; //Increment TMR0 on rising clock edge

PSA = 0; //Assign prescaler to Timer0

//Select a 1:32 prescaler

PS0 = 0;

PS1 = 0;

PS2 = 1;

//Initialize the direction flag to shift bits from right-to-left //(i.e. 0 = Shift PORTC bits from right-to-left // 1 = Shift PORTC bits from left-to-right

direction = 0; //Initialize LED_Output to all zeros

LED_Output = 0b00000000;

//Configure for RA2 Interrupt-On-Change

IOCA2 = 1; //Enable RA2 interrupt-on-change

RABIE = 1; //Enable change interrupts

RABIF = 0; //Clear the change interrupt flag

GIE = 1;//Enable interrupt capability on the

//PIC16F690 ***ALWAYS DONE LAST*****

//Read PORTA to latch the current RA2 voltage level

PORTA = PORTA;

EXAMPLE 3-28: INITIALIZE() CODE FOR GPIO LAB 8

PICDEMTM Lab Development Board User’s Gu ide

3.4.7.4 TESTING THE APPLICATION

Program the PIC16F690. The application should operate exactly as it did in the previous lab. Only this time with the absence of the 10 K

The solution for this project is located in the C:\PICDEM_Lab\GPIO_Labs\GPIO_Lab8\solution directory.

Ω pull-up resistor.

Chapter 4. Comparator Peripheral Labs

4.1 INTRODUCTION

The following labs cover some of the fundamental features of the Comparator 1 peripheral found on the PIC16F690 including some unique applications. These peripherals are very useful mixed signal building blocks as they provide analog functionality independent of program execution. The labs in this section will demonstrate this functionality, then introduce intelligence to implement a relatively high resolution temperature sensor measurement application.

4.2 COMPARATOR LABS

4.2.1 Reference Documentation

All documentation is available on the PICDEM™ Lab Development Kit accompanying CD-ROM:

• PIC16F690 Data Sheet (DS41262)

- Section 4.0: I/O Ports

- Section 5.0: Timer0 Module

- Section 6.0: Timer1 Module

- Section 8.0: Comparator Module

• “Introduction to MPLAB Family Lite Mode Compiler Tutorial” (DS41322)

PICDEMTM LAB DEVELOPMENT

BOARD USER’S GUIDE

IDE and HI-TECH C® PRO for the PIC10/12/16 MCU

4.2.2 Comparator Labs

The labs that will be implemented in this chapter are:

• Lab 1: Simple Comparator

• Lab 2: Using the Internal Comparator Voltage Reference

• Lab 3: Higher Resolution Sensor Readings Using a Single Comparator

4.2.3 Equipment Required

To complete the labs in this section, the following components are required:

1. 2 – 10 KΩ resistors

2. 4 – 470Ω resistor

3. 1 – 100 KΩ potentiometer

4. 4 – Light Emitting Diodes

5. 1 – 1N4148 diodes

6. 1 – 1 μF capacitor

7. PIC16F690 populating socket U2

8. Assorted jumper wires

PICDEMTM Lab Development Board User’s Gu ide

1 2 3 4 5 6 7 8 9

20 19 18 17 16 15 14 13 12 11

C1IN+

J9J8

R4 470Ω

LED1

C12IN0-

C1OUT

R1 10KΩ

R2 10KΩ

R3 100KΩ

4.2.4 Lab 1: Simple Compare

4.2.4.1 NEW REGISTERS USED IN THIS LAB

To configure the peripherals used in this lab, the following registers are used:

1. Comparator C1 Control Register 0: CM1CON0 (Register 8-1 in Section 8 of the PIC16F690 Data Sheet)

- Enables Comparator C1.

- Configures Comparator output polarity.

- Enables the Comparator result to be available internal only or on the C1OUT pin (pin 17).

- Select inverting and non-inverting Comparator 1 reference input sources.

4.2.4.2 OVERVIEW

In this lab, Comparator 1 on the PIC16F690 is configured to perform a simple compare. A potentiometer connected to the inverting input (C12IN0-) of the comparator will be compared against the 2.5V connected to the non-inverting input (C1IN+) from a simple voltage divider circuit. An LED connected to the output of Comparator 1 (C1OUT) will light or turn off as follows:

• inverting reference > non-inverting reference = C1OUT is low = LED OFF

• inverting reference < non-inverting reference = C1OUT is high = LED ON

The PICDEM™ Development Board configuration schematic is shown in Figure 4-1.

FIGURE 4-1: SCHEMATIC FOR COMPARATOR LAB 1

The software flowchart for this lab is shown in Figure 4-2.

Comparator Peripheral Labs

main()

Initialize()

Loop Forever

Wait

//Initialize Comparator 1 as follows:

//Turn comparator 1 on C1ON = 1;

//Make the comparator output available on the //C1OUT pin C1OE = 1;

//Select the non-inverting pin (C1IN+) as the //non-inverting reference input for the comparator 1 C1R = 0;

//Select the C12IN0- pin as the inverting reference C1CH0 = 0; C1CH1 = 0;

//Since the comparator 1 output shares the same pin //as PORTA bit 2, configure the corresponding TRISA2 bit //as an output TRISA2 = 0;

FIGURE 4-2: MAIN() SOFTWARE CONTROL LOOP FLOWCHART FOR

COMPARATOR LAB 1

As mentioned in the introduction, comparators on the PIC16F690 are able to function independent of software logic. Therefore, all that is needed is to call the Initialize() from main() to activate the peripheral. The Initialize() configures Comparator 1 as follows:

• Turn on Comparator 1

• Make the Comparator 1 output available on the C1OUT pin

• Select pin C1IN+ as the non-inverting reference

• Select pin C12IN0- as the inverting reference

• Configure the C1OUT pin as an output

4.2.4.3 PROCEDURE

Using the Project Wizard, create a new project using the PIC16F690 entitled

Comparator_Lab1.mcp as was done in previous labs. Once completed, open the Comparator_Lab2.c source file in MPLAB and do the following:

1. Copy/paste the code in Example 4-1 into the Initialize() section labeled:

//ADD INITIALIZE CODE HERE

EXAMPLE 4-1: INITIALIZE CODE FOR COMPARATOR LAB 1

PICDEMTM Lab Development Board User’s Gu ide

Initialize(); //Initialize the relevant registers while(1);

2. Copy/paste the code in Example 4-2 into the main() section labeled: //ADD MAIN CODE HERE

EXAMPLE 4-2: MAIN() CODE FOR COMPARATOR LAB 1

Note: The inclusion of the while loop forces the microcontroller to sit and wait at

a “known” instruction. At start-up, the contents of the program memory are unknown. Without the while loop, the microcontroller will continue to run through each address in program memory executing whatever resides at a particular address. This could have adverse effects on the application.

3. Compile the project. There should be no errors.

4.2.4.4 TESTING THE APPLICATION

Program the PIC16F690. The LED connected to the C1OUT pin should light when the voltage present on the C12IN0- pin is less than the 2.5V present on the C1IN+ pin and turn off when the 2.5V is exceeded.

The solution for this project is located in the C:\PICDEM_Lab\Comparator_Labs\Comparator_Lab1\solution directory.

Note: This application uses two pins that are used during the programming pro-

cess (ICSPDATA and ICSPCLK). The jumper wires connecting these pins to the application circuit may need to be disconnected while programming if there are problems with the MPLAB IDE connecting to the PIC16F690.

4.2.5 Lab 2: Using the Comparator Voltage Reference

4.2.5.1 NEW REGISTERS USED IN THIS LAB

To configure the peripherals used in this lab, the following registers are used:

1. Voltage Reference Control Register: VRCON (Register 8-5 in Section 8 of the PIC16F690 Data Sheet).

- Enables either the Comparator Voltage Reference or the 0.6V constant reference as the non-inverting reference input to Comparator C1 or Comparator C2.

- Selects either a High or Low resolution 16-level voltage range.

- Enable a 0.6V reference.

- Uses three bits to configure the reference voltage level.

4.2.5.2 OVERVIEW

This lab expands on Lab 1 by utilizing the internal Comparator Voltage Reference (CV

REF) feature on the PIC16F690. The CVREF provides an internally generated

voltage reference that can be used by the Comparator 1 non-inverting reference input so that external components are not needed such as the resistor voltage divider used in the previous lab. The CV

• Independent comparator operation

• Two 16-level voltage ranges

• Ratiometric with V

REF features:

Comparator Peripheral Labs

VRR = 1 (Low-Range):

CVREF = (VR<3:0>/24) x VDD

VRR = 0 (High-Range):

CVREF = (VDD/4) + (VR<3:0> x VDD/32)

VRR = 1 (Low-Range):

CVREF = (VR<3:0>/24) x VDD

Known: desired CVREF = 2.5V, VDD approximately 5V

Therefore:

2.5V = (VR<3:0>/24 x 5V

2.5V/5V = (VR<3:0>/24) (2.5V/5V) x 24 = VR<3:0> VR<3:0> = 12

or 11002

VR0 = 0 VR1 = 0 VR2 = 1 VR3 = 1

• Fixed 0.6 reference option

• Output clamped to V

The CVREF has 2 ranges with 16 voltage levels in each range. Range selection is controlled by the CV Control Register) along with the CV Selection bits hold a value based upon some simple calculations to set the internal reference voltage. The CV

REF Range Selection (VRR) bit in the VRCON (Voltage Reference

REF

Value Selection bits (VR<3:0>). The Value

REF voltage is determined using Equation 4-1:

EQUATION 4-1: CV

REF OUTPUT VOLTAGE

This lab will implement the low-range calculation by setting the VRR bit in VRCON equal to 1. Equation 4-2 demonstrates how to calculate the VR<3:0> values, using the low-range method, to obtain a 2.5V internal reference. If higher resolutions are required, the high-range method should be used (see Section 8.10.2 in the PIC16F690 Data Sheet (DS-41262).

EQUATION 4-2: CALCULATING A 2.5V INTERNAL REFERENCE

(LOW-RANGE METHOD)

The Initialize() from the previous lab now must configure both the Comparator 1 peripheral and the CV

• Turn on Comparator 1

•Select CV

REF the non-inverting reference for Comparator 1

• Continue to use the C12IN0- pin as the inverting reference

• Turn on CV

• Select the low-range feature

• Set the CV

Changes to the PICDEM™ Development Board configuration schematic for this lab are shown in Figure 4-3.

REF as follows:

REF

REF Value Selection bits as per the calculation in Equation 4-2.

PICDEMTM Lab Development Board User’s Gu ide

1 2 3 4 5 6 7 8 9

20 19 18 17 16 15 14 13 12 11

J9J8

R4 470Ω

LED1

C12IN0-

C1OUT

R3 100KΩ

FIGURE 4-3: SCHEMATIC FOR COMPARATOR LAB 2

4.2.5.3 PROCEDURE

Using the firmware developed in the previous lab, make the following changes:

1. Copy/paste the code in Example 4-3 into the Initialize() over the code

from the previous lab.

Comparator Peripheral Labs

//Intialize Comparator 1 as follows:

//Turn comparator 1 on C1ON = 1;

//Make the comparator output available on the //C1OUT pin C1OE = 1;

//Select the internal voltage reference //as the non-inverting reference voltage C1R = 1;

//Select the C12IN0- pin as the inverting reference C1CH0 = 0; C1CH1 = 0;

//Initialize the internal voltage reference as follows:

//Turn on the CVref output and route to the C1Vref input //of comparator 1 C1VREN = 1;

//Use the comparator voltage low range feature VRR = 1;

//Set the comparator voltage reference value selection //to 2.5V by making the VR<3:0> bits equal to 12 or //binary 1100 (see lab manual for equations) VR0 = 0; VR1 = 0; VR2 = 1; VR3 = 1;

//Since the comparator 1 output shares the same pin //as PORTA bit 2, configure the corresponding TRISA2 bit //as an output TRISA2 = 0;

EXAMPLE 4-3: INITIALIZE CODE FOR COMPARATOR LAB 2

2. The main() stays the same as the previous lab.

3. Compile the project. There should be no errors.

4.2.5.4 TESTING THE APPLICATION

Program the PIC16F690. The application should behave exactly as it did in the previous lab with the exception of less components used.

The solution for this project is located in the C:\PICDEM_Lab\Comparator_Labs\Comparator_Lab2\solution directory.

PICDEMTM Lab Development Board User’s Gu ide

+ _

0.6V

PIC16F690

C1OUT

C12IN0-

4.2.6 Lab 3: Higher Resolution Sensor Readings Using a Single Comparator

4.2.6.1 NEW REGISTERS USED IN THIS LAB

To configure the peripherals used in this lab, the following registers are used:

1. Timer1 Control Register: T1CON (Register 6-1 in Section 6 of the PIC16F690

data sheet)

- This register is used to control Timer1 and select various features of the module. In this lab the register will be used to enable Timer1 and select the clock source.

4.2.6.2 OVERVIEW

This lab expands on concepts discussed in the previous comparator lab by implementing intelligence to create a higher resolution temperature sensor measurement application. The comparator will be configured to operate as a simple relaxation oscillator with the addition of a few external components. The internal voltage reference will still be used to provide the non-inverting reference only this time the 0.6V fixed voltage reference feature will be implemented.

The basic oscillator circuit is shown in Figure 4-4.

FIGURE 4-4: BASIC RELAXATION OSCILLATOR CIRCUIT

Referring to Figure 4-4, at start-up, the capacitor connected to the inverting reference of Comparator 1 is completely discharged. Therefore, the voltage present on the inverting reference is 0V which is less than the 0.6V fixed voltage reference on the non-inverting reference and Comparator 1’s output goes high. This rapidly charges the capacitor through the diode (D1) to a level approximately equal to V parator detects that the inverting reference input is greater than the 0.6V fixed voltage reference, the output transitions low. The charge across the capacitor then discharges slowly across the resistor R1. Once the capacitor charge drops below the 0.6V fixed

DD. Once the Com-

Comparator Peripheral Labs

1 2 3 4 5 6 7 8 9

20 19 18 17 16 15 14 13 12

C12IN0C1OUT

R1 100KΩ

D1 1N4148

C1 1μF

R3 10KΩ NTC thermistor

R7 470Ω

LED4

RC0 RC1 RC2

T1CKI

RC3

R6 470Ω

LED3

R5 470Ω

LED2

R4 470Ω

LED1

R2 10KΩ

reference, the cycle repeats and the system oscillates. The frequency of this oscillation is dependant on the RC time constant ( capacitor to 37% of its initial voltage. As either the resistance or capacitance decreases, so will

τ effectively increasing the frequency of the oscillator. If the resistor

is replaced with a Negative Temperature Coefficient (NTC) thermistor where resistance decreases as temperature increases, any temperature change would cause a shift in resistance with a subsequent shift in the frequency of the oscillator.

This oscillator can be created quite easily by simply initializing the comparator and nothing more. However, with the addition of some intelligence and some additional peripherals, a high resolution sensor measurement application can be achieved.

The PIC16F690 features a 16-bit timer/counter peripheral Timer1. This timer can either use the internal instruction clock (F on the Timer1 Clock Input (T1CKI) pin to increment two 8-bit registers, TMR1H and TMR1L, to obtain a combined 16-bit result. In this application, the oscillator described will be used as the Timer1 clock source. Therefore, the TMR1H:TMR1L will increment with each low-to-high transition effectively counting the number of pulses. The Timer0 peripheral features an interrupt-on-overflow (255-0) that will be used to provide a fixed time frame in which the TMR1H:TMR1L registers will count. On a Timer0 overflow interrupt, the Timer1 peripheral stops counting and the current value in the upper 4-bits of TMR1H will be output to four LEDs connected to PORTC pins RC3, RC2, RC1 and RC0. In order to obtain a usable result, it is important that Timer0 triggers an interrupt before the TMR1H:TMR1L result overflows. If the temperature to the thermistor changes, the oscillator frequency will shift resulting in a change in the number of counts the Timer1 peripheral was able to implement before the fixed Timer0 interrupt with a different result displayed on the LEDs.

The schematic for this lab is shown in Figure 4-5.

τ = R x C), or the time it takes to discharge the

OSC/4) as its time base or an external clock source

FIGURE 4-5: SCHEMATIC FOR COMPARATOR LAB 3

PICDEMTM Lab Development Board User’s Gu ide

main()

Initialize()

Loop Forever

Wait

The software flowchart for this lab is shown in Figure 4-6.

FIGURE 4-6: MAIN() SOFTWARE CONTROL LOOP FLOWCHART FOR

COMPARATOR LAB 3

The Initialize() configures the PIC16F690 as follows:

• Configure PORTC pins RC0, RC1, RC2 and RC3 and digital outputs

•Comparator 1

- Enable Comparator 1.

- Make the Comparator 1 output available on the C1OUT pin configuring TRISA2 as an output.

- Route the CV

- Select pin C12IN0- as the inverting reference configuring TRISA1 as an input.

- Configure the C1OUT pin as an output.

•CV

REF Configuration:

-Configure CV reference of Comparator 1.

• Timer1 Configuration:

- Select the T1CKI pin as the Timer1 clock source making TRISA5 an input.

- Clear both Timer1 result registers TMR1H:TMR1L.

- Turn on Timer1.

•Timer0

-Select F

- Assign the prescaler to Timer0 and configure so that the TMR0 register increments every 256th clock pulse.

- Enable Timer0 interrupt-on-overflow

- Clear the Timer0 interrupt flag

- Preload TMR0 with 10 (this ensures that a Timer0 interrupt will occur before the Timer1 registers overflow).

- Enable Global Interrupts on the PIC16F690.

The Interrupt Service Routine, TMR0_ISR(), is shown in Figure 4-7.

REF output to the non-inverting reference input.

REF to route the 0.6V fixed voltage reference to the non-inverting

OSC/4 as the Timer0 clock source.

Comparator Peripheral Labs

END

TMR0_ISR()

T0IF = 1

Clear T0IF Flag

Turn off Timer1

Assign PORTC the T1MRH value

shifted 4 bits to the right

Clear the Timer1 result register

pair TMR1H:TMR1L

Turn on Tim er1

YES

Keep PORTC the same

FIGURE 4-7: TMR0_ISR FLOWCHART FOR COMPARATOR LAB 3

The TMR0_ISR() first checks if a Timer0 interrupt has occurred (good programming practice). If so, then the Timer0 interrupt flag is cleared and Timer1 is turned off to stop counting the oscillator clock pulses on the T1CKI pin. Next, the 4 MSbs of the Timer1 16-bit result is assigned to the RC0, RC1, RC2 and RC3 pins to light the associated LEDs. Finally, the Timer1 result register pair are cleared and Timer1 is turned on to begin a new count.

4.2.6.3 PROCEDURE

Using the firmware developed in the previous lab, make the following changes:

1. Copy/paste the code in Example 4-4 into the top of the main firmware source file

under the heading labeled:

//----------------INTERRUPT CODE---------------

PICDEMTM Lab Development Board User’s Gu ide

void interrupt TMR0_ISR(void) {

//Check if Timer0 interrupt has occurred

if(T0IE&&T0IF) {

//if so, clear the interrupt flag T0IF = 0; //Turn off Timer1 (stop counting) TMR1ON = 0; //Assign the upper 4-bits of the 16-bit //result to PORTC to light the LEDs connected //RC0,R1,RC2 and RC3 PORTC = TMR1H>>4; TMR0 = 10; //Clear the Timer1 register pair TMR1L = 0; TMR1H = 0; //Turn Timer1 back to start counting again

TMR1ON = 1; } else PORTC = PORTC;

}

EXAMPLE 4-4: TMR0_ISR CODE FOR LAB 3

2. Copy/paste the code in Example 4-5 into the Initialize() over the code

from the previous lab:

Comparator Peripheral Labs

//Configure RC0,RC1,RC2 and RC3 as digital outputs

ANSEL = 0b00001111; PORTC = 0; TRISC0 = 0; TRISC1 = 0; TRISC2 = 0; TRISC3 = 0;

//Initialize PORTA pin connected to C12IN0-

TRISA1 = 1;

//Make C1OUT pin an output

TRISA2 = 0; //Configure the Comparator 1 as follows: //Turn on comparator 1

C1ON = 1; //Make C1OUT available externally

C1OE = 1; //Connect the non-inverting reference to CVREF

C1R = 1; //Connect the inverting reference to C12IN0-

C1CH0 = 0;

C1CH1 = 0; //Configure the CVREF as follows: //Route CVREF output to Comparator 1 non-inverting reference

VRCON = 0; //Enable the 0.6V fixed reference voltage

VP6EN = 1; //Configure Timer1 as follows //Make T1CKI and input

TRISA5 = 1;

T1CON = 0; //Select T1CKI as Timer1's clock source

TMR1CS = 1; //Initialize the 16-bit Timer1 register pair to 0

TMR1H = 0;

TMR1L = 0; //Turn on Timer1

TMR1ON = 1; //Set up Timer0 as follows: //Use FOSC/4 for Timer0 Clock Source

OPTION = 0;

T0CS = 0; //assign the prescaler to TMR0

PSA = 0; //set up prescaler for 1:256

PS0 = 1;

PS1 = 1;

PS2 = 1; //Enable Timer0 Interrupts

T0IE = 1; //Clear the Timer0 overflow interrupt flag

T0IF = 0; //Preload TMR0 with 10 to keep overflow period //less than Timer1 overflow period

TMR0 = 10; //Enable global interrupts

GIE = 1;

EXAMPLE 4-5: INITIALIZE CODE FOR COMPARATOR LAB 3

PICDEMTM Lab Development Board User’s Gu ide

Initialize(); //Initialize the relevant registers while(1);

3. Copy/paste the code in Example 4-6 into the main() over the code from the

previous lab:

EXAMPLE 4-6: MAIN() CODE FOR COMPARATOR LAB 3

4. Compile the project. There should be no errors.

4.2.6.4 TESTING THE APPLICATION

Program the PIC16F690. Adjust the R1 potentiometer until the LEDs begin to light displaying a binary value. Touching the thermistor should introduce heat, reduce the frequency of oscillation and increase the binary count on the LED display. Introducing cold to the thermistor should have the opposite effect thereby decreasing the binary count.

The solution for this project is located in the C:\PICDEM_Lab\Comparator_Lab\Comparator_Lab3\solution directory

PICDEMTM LAB DEVELOPMENT

BOARD USER’S GUIDE

Chapter 5. Analog-to-Digital Converter Peripheral Labs

5.1 INTRODUCTION

The Analog-to-Digital Converter (ADC) peripheral allows conversion of an analog input signal to a 10-bit binary value representing that signal so that it can be used in firmware.

The following labs cover some of the fundamental features of the Analog-to-Digital Converter (ADC) peripheral found on the PIC16F690 including some unique applications.

5.2 ADC LABS

The labs that will be implemented in this chapter are:

• Lab 1: Simple ADC

• Lab 2: Audible Temperature Sensor

5.2.1 Reference Documentation

All documentation is available on the PICDEM™ Lab Development Kit accompanying CD-ROM

• PIC16F690 Data Sheet (DS41262)

- Section 4: I/O Ports

- Section 5: Timer0 Module

- Section 9: Analog-to-Digital Converter (ADC) Module

• Timers: Timer0 Tutorial (Part 1) (DS51628)

• Timers: Timer0 Tutorial (Part 2) (DS51702)

• “Introduction to MPLAB Family Lite Mode Compiler Tutorial” (DS41322)

IDE and HI-TECH C® PRO for the PIC10/12/16 MCU

5.2.2 Equipment Required

To complete the labs in this section, the following components are required:

1. 1 – 100

2. 4 – 470

3. 1 – 1K

4. 1 – 10 K

5. 1 – 100 K

6. 1 – 10 K

7. 4 – Light Emitting Diodes

8. 1 – IRFD010 N-Channel MOSFET

9. PIC16F690 populating socket U2

10. Assorted jumper wires

Ω resistor Ω resistors

Ω resistor

Ω potentiometer

Ω NTC Thermistor

PICDEMTM Lab Development Board User’s Gu ide

5.2.3 Lab 1: Simple ADC

5.2.3.1 NEW REGISTERS USED IN THIS LAB

To configure the peripherals used in this lab, the following registers are used:

1. ADC Control Register 0: ADCON0 (Register 9-1 in Section 9 of the PIC16F690 Data Sheet)

- Configures ADC conversion result justification.

- Select ADC reference voltage.

- Selects ADC input channel (i.e., pin with analog voltage to be converted).

- Starts ADC conversion and determines when ADC conversion is complete.

- Enables the ADC peripheral.

2. ADC Control Register 1: ADCON1 (Register 9-2 in Section 9 of the PIC16F690 Data Sheet)

- Determines ADC conversion clock.

3. ADC Result Register high: ADRESH (see Register 9-3 in Section 9 of the PIC16F690 Data Sheet)

- Holds upper 8-bits or upper 2-bits (depending on justification selected) of 10-bit ADC conversion result.

4. ADC Result Register low: ADRESL (see Register 9-4 in Section 9 of the PIC16F690 Data Sheet)

- Holds lower 8-bits or lower 2-bit (depending on justification selected) of 10-bit ADC conversion result.

5.2.3.2 OVERVIEW

In this lab, the ADC peripheral on the PIC16F690 is used to perform a simple conversion of an analog voltage present on pin 13. The voltage is varied using a 100K

Ω potentiometer. This voltage is compared against a reference voltage to

generate a 10-bit binary result via successive approximation stored into two 8-bit ADC result registers ADRESH and ADRESL. The ADC result is software selectable as either left or right justified as shown in Section 9.1.6 of the PIC16F690 Data Sheet. This application will configure the ADC result as left justified with the four Most Significant bits of the 10-bit result output to the RC0, RC1,RC2 and RC3 PORTC pins used to light connected LEDs accordingly.The PICDEM™ Development Board configuration schematic is shown in Figure 5-1.

Analog-to-Digital Converter Peripheral Labs

1 2 3 4 5 6 7 8 9

20 19 18 17 16 15 14 13 12 11

J9J8

R3 470Ω

LED3

R5 100KΩ

RB4/AN10

RC0 RC1 RC2

RC3

R2 470Ω

LED2

R1 470Ω

LED1

R4 470Ω

LED4

main()

Initialize()

Loop Forever

Get_Inputs()

Decide()

Do_Outputs()

Global variables initialized:

• 8-bit var ia ble LED_output will be used to light the three LEDs connected to PORTC

FIGURE 5-1: SCHEMATIC FOR ADC LAB 1

The voltage reference is software selectable as either V applied to the external reference pin 18 (V application makes use of V

as the reference.

REF). To minimize circuit complexity, this

DD or an external voltage

The software flowchart for this lab is shown in Figure 5-2.

FIGURE 5-2: MAIN() SOFTWARE CONTROL LOOP FLOWCHART FOR

COMPARATOR LAB 1

PICDEMTM Lab Development Board User’s Gu ide

The Initialize() configures the peripherals as follows:

•Ports

- Configure pin 13 as an analog input (using TRISB4).

- Clear the PORTC register.

- Configure RC0, RC1, RC2 and RC3 pins as digital output.

•ADC

- Select ADC conversion clock F

- Configure voltage reference using VDD.

- Select channel 10 as the ADC input channel (Pin 13: RB4/AN10).

- Select result format left justified (10-bit result in ADRESH<7:0> and ADRESL<7:6>).

- Turn on ADC module.

Note: The ADC conversion clock is the time that will be used to convert the analog

voltage present on pin 13 to a 10-bit value in the ADRESH:ADRESL registers. It takes 11 of these conversion clock cycles to perform a complete ADC. If the conversion clock period is insufficient, an incomplete ADC result will occur. The electrical specifications for the PIC16F690 state that the conversion clock must have a period of at least 1.5 quency of approximately 667 kHz. The ADC Module section of the data sheet specifies acceptable conversion clock frequencies depending on the main oscillator used to drive the microcontroller and should be referenced. In this application, a dedicated internal oscillator for the ADC module is used ensuring a conversion clock frequency of between 2-6 (see Table 17-16 in Section 17 of the PIC16F690 Data Sheet).

μSeconds or a fre-

μSeconds.

Next, the Get_Inputs() performs an ADC on the voltage present on pin 13. The internal capacitor connected to the input of the ADC peripheral needs time to charge to the voltage present on the pin. Therefore, software will need to implement a short delay to allow for this charging time. The ADC Module section “A/D Acquisition Requirements” of the data sheet goes into great detail and includes an equation for selecting an appropriate acquisition time. For the purposes of this lab, a simple 1mS delay should be more than sufficient. These parameters become important in high-speed applications where every μS counts.

The GO/DONE bit also serves as a flag that indicates when the ADC is completed (GO/DONE Therefore, the Get_Inputs() initiates an ADC by setting GO/DONE waits for the bit to clear indicating a completed conversion.

The software flowchart for the Get_Inputs() is shown in Figure 5-3.

bit in ADCON0 is used to start the ADC process when set to ‘1’. This

= 0).

then sits and

Analog-to-Digital Converter Peripheral Labs

Get_Inputs()

Delay_1mS()

Start conversion by setting

GO/DONE

bit

Gives ADC capacitor time to charge

GO/DONE = 1

YES

END

Wait for ADC to complete

unsigned char LED_Output = 0;//assigned to PORTC to light

//connected LEDs

FIGURE 5-3: MAIN() SOFTWARE CONTROL LOOP FLOWCHART FOR

COMPARATOR LAB 1

Following the Get_Inputs(), the 10-bit ADC result is now in the ADRESH:ADRESL registers. The Decide() assigns the ADC result value, shifted four bit positions to the right, to the LED_Output variable.

Finally, the Do_Outputs() assigns the contents of LED_Output to the PORTC register that will light the LEDs connected to RC0, RC1, RC2 and RC3 accordingly.

5.2.3.3 PROCEDURE

Using the Project Wizard, create a new project called ADC_Lab1.mcp. Once completed, open the ADC_Lab1.c source file in MPLAB and make the following changes:

1. Copy/paste the code in Example 5-1 into the top of the main firmware source file

under the heading labeled:

//----------------DATA MEMORY---------------

EXAMPLE 5-1: GLOBAL VARIABLES USED IN LAB 1

2. Copy/paste the code in Example 5-2 into the top of the main firmware source file

under the heading labeled:

//----------------SUPPORT ROUTINES---------------

PICDEMTM Lab Development Board User’s Gu ide

/*---------------------------------------------------------

Subroutine: Delay_1mS Parameters: none Returns:nothing Synopsys:Creates a 1mS delay when called

---------------------------------------------------------*/ void Delay_1mS(void) {

unsigned int delay_var = 98; //Keep looping until the delay_var is // equal to zero (should take 1mS) while(--delay_var);

}

EXAMPLE 5-2: DELAY_1MS() CODE FOR ADC LAB 1

3. Copy/paste the code in Example 5-3 into the Initialize() section labeled: //ADD INITIALIZE CODE HERE

Analog-to-Digital Converter Peripheral Labs

//Configure Port:

//Disable pin output driver (See TRIS register) TRISB4 = 1;

// Configure pin as analog ANS10 = 1;

//Configure RC0, RC1, RC2 and RC3 as digital output PORTC = 0; TRISC0 = 0; TRISC1 = 0; TRISC2 = 0; TRISC3 = 0;

ANS4 = 0; ANS5 = 0; ANS6 = 0; ANS7 = 0;

//Configure the ADC module:

//Select ADC conversion clock Frc ADCS0 = 1; ADCS1 = 1; ADCS2 = 1;

//Configure voltage reference using VDD VCFG = 0;

//Select ADC input channel Pin 13 (RB4/AN10) CHS0 = 0; CHS1 = 1; CHS2 = 0; CHS3 = 1;

//Select result format left justified ADFM = 0;

//Turn on ADC module ADON = 1;

EXAMPLE 5-3: INITIALIZE CODE FOR COMPARATOR LAB 1

4. Copy/paste the code in Example 5-4 into the Get_Inputs() section labeled:

//ADD GET INPUTS CODE HERE

PICDEMTM Lab Development Board User’s Gu ide

//Perform an ADC of potentiometer connected to pin 13

//Wait the required acquisition time Delay_1mS();

//Start conversion by setting the GO/DONE bit. GODONE = 1;

//Wait for ADC conversion to complete //Polling the GO/DONE bit // 0 = ADC completed // 1 = ADC in progress while(GODONE == 1);

//Assign the upper 4 bits of ADRESH to the lower 4 bits //of LED_Output LED_Output = ADRESH >> 4; //Shifts the bits in ADRESL 4 bits

//to the right

//Assign contents of LED_Output to PORTC to light the connected //LEDs PORTC = LED_Output;

Initialize(); //Initialize the relevant registers while(1) {

Get_Inputs(); Decide(); Do_Outputs();

}

EXAMPLE 5-4: GET_INPUTS() CODE FOR ADC LAB 1

5. Copy/paste the code in Example 5-5 into the Decide() section labeled: //ADD DECIDE CODE HERE

EXAMPLE 5-5: DECIDE() CODE FOR ADC LAB 1

6. Copy/paste the code in Example 5-6 into the Do_Outputs() section labeled: //ADD DO OUTPUTS CODE HERE

EXAMPLE 5-6: D0_OUTPUTS() CODE FOR ADC LAB 1

7. Copy/paste the code in Example 5-7 into the main() section labeled: //ADD MAIN CODE HERE

EXAMPLE 5-7: MAIN() CODE FOR ADC LAB 1

8. Compile the project. There should be no errors.

Analog-to-Digital Converter Peripheral Labs

1 2

1 4

1 8

128

256

512

1024

10-BIT ADC RESULT (ADRESH: ADRESL)

Example:

If following an ADC, the ADRESH:ADRESL contains the following 10-bit value:

10-BIT ADC RESULT (ADRESH: ADRESL)

1100100001

1024

2.5V

1.25V

0.15625V

0.000488V

3.911V (rounded to the nearest mV)

Note: Assumes that VDD is used as the ADC reference. If an external

reference is used, the voltage present on V

REF pin is substituted

for V

DD.

Bit positions set to ‘1’ are added together

5.2.3.4 TESTING THE APPLICATION

Program the PIC16F690. Turning the potentiometer connected to pin 13 should light the LEDs sequentially in a binary fashion. Note that these are the 4 Most Significant bits of the ADC result. Adding 6 more LEDs and I/O pins would allow the complete 10-bit value to be displayed. To determine the significance of each bit in the ADRESH:ADRESL 10-bit result, see Figure 5-4.

FIGURE 5-4: ADC RESULT BIT SIGNIFICANCE

Note: Using a 5V reference voltage with a 10-bit provides a resolution of

0.000488V or 4.88mV (5V/1024).

PICDEMTM Lab Development Board User’s Gu ide

Since this lab outputs the 4 Most Significant bits of the ADC result and VDD is used as the reference voltage, the LED display should correspond with the following voltage levels shown in Table 5-1.

T ABLE 5-1: CORRESPONDING VOLT AGE ON PIN 13 RELATED TO LIT LEDS

(1 = LED ON, 0 = LED OFF)

LED4 LED3 LED2 LED1 pin 13 Voltage

0000 < 0.3125V

0001 > 0.3125V

0010 > 0.625V

0011 > 0.9375V

0100 > 1.25V

0101 > 1.5625V

0110 > 1.875V

0111 > 2.1875V

1000 > 2.5V

1001 > 2.8125V

1010 > 3.125V

1011 > 3.4375V

1100 > 3.75V

1101 > 4.0625V

1110 > 4.375V

1111 > 4.6875V or greater

Note: The greater than symbol (>) is required since the lower 6 bits of the ADC

result are not shown using LEDs.

The solution for this project is located in the C:\PICDEM_Lab\ADC_Labs\ADC_Lab1\solution directory.

Analog-to-Digital Converter Peripheral Labs

1 2 3 4 5 6 7 8 9 10

20 19 18 17 16 15 14 13 12 11

J9J8

R1 1KΩ

RB4/AN10

RC0

R3 100Ω

8Ω

R2 10KΩ

J19

SP+

SP-

LS1

Thermistor

Q1 IRFD010 N-Channel

MOSFET

R4 10KΩ

5.2.4 Lab 2: Audible Temperature Sensor

5.2.4.1 OVERVIEW

In this lab, the ADC peripheral on the PIC16F690 is used to alter the frequency of Pulse-Width Modulated Waveform (PWM) in relation to the temperature sensed by a thermistor connected to the input of the ADC peripheral. The PWM waveform is generated by simply toggling the RC0 voltage level high and low. The thermistor is used to create a voltage divider in conjunction with a 1KΩ ADC input. This thermistor is a Negative Temperature Coefficient type (NTC) meaning that as the temperature of the device increases, the resistance effectively decreases. The voltage drop across the thermistor is converted by the ADC and the ADRESH result then used to manipulate a TMR0 preload value (see GPIO Lab 3) that will be used in the Timing() to vary the execution speed of the software control loop and ultimately the frequency of the PWM waveform. The PWM will be connected to an N-Channel MOSFET used to drive the 8Ω

speaker on the PICDEM Lab Development

Board. The schematic for this lab is shown in Figure 5-5.

FIGURE 5-5: SCHEMATIC FOR ADC LAB 2

resistor to vary the voltage into the

Referring to the schematic in Figure 5-5, the RC0 connects to the gate of the IRFD010 N-Channel MOSFET Q1. Resistor R4 pulls the gate input low ensuring the transistor will remain OFF until a high voltage level is present on the RC0 output. When the PWM transitions high, Q1 is ON and current flows through the 8Ω resistor is used to limit the current through the speaker to maintain manufacturer spec-

speaker. The 100Ω R3

ified power ratings. In this way, any change in temperature around the thermistor will

alter the frequency of the PWM, thereby changing the audible frequency emitted from the speaker.

PICDEMTM Lab Development Board User’s Gu ide

main()

Initialize()

Loop Forever

Get_Inputs()

Decide()

Do_Outputs()

Global variables initialized:

• 8-bit variable TMR0_preload will be used to vary the delay in Timing() to alter the frequency of the PWM output on RC0

Timing()

The audible frequency range is between 20-20000Hz. Therefore, the Timing() delays from a maximum of 4.096 mS (244.1Hz) to a minimum of 1.536 mS (651Hz). These values are determined using the internal instruction clock (F clock source with a prescaler of 1:16. Other values could easily be used as long as the frequency of the PWM remains within the audible range.

The software flowchart for this lab is shown in Figure 5-6.

FIGURE 5-6: MAIN() SOFTWARE CONTROL LOOP FLOWCHART FOR

ADC LAB 2

OSC/4) as the TMR0

The Initialize() configures the peripherals as follows:

•Ports

-Clear PORTB.

- Configure pin 13 as an analog input (using TRISB4).

- Clear the PORTC register.

- Configure RC0 pin as digital output.

•Timer0

- Select the F

- Increment TMR0 on the low-to-high transition of F

- Assign the prescaler to Timer0 and configure at a rate of 1:16.

•ADC

- Select ADC conversion clock F

- Configure voltage reference using VDD.

- Select channel 10 as the ADC input channel (Pin 13: RB4/AN10).

- Select result format left justified (10-bit result in ADRESH<7:0> and ADRESL<7:6>).

- Turn on ADC module.

OSC/4 internal instruction clock as the Timer0 clock source.

OSC/4.

Analog-to-Digital Converter Peripheral Labs

unsigned char LED_Output = 0; //assigned to PORTC to light

//connected LEDs

bit toggle = 0;//Used to generate waveform on RC0

unsigned char TMR0_preload = 0; //Varied by ADRESH to change

//frequency of

//waveform on RC0

Next, the Get_Inputs() performs an ADC on the voltage present on pin 13 using the same code as Lab 1 with one minor change. This application is very dependant on the timing of the software control loop. The 1mS delay used in Lab 1 to allow the hold capacitor on the input of ADC to fully charge to the pin voltage is excessive. Using the example given in Equation 9-1, Section 9 in the PIC16F690 Data Sheet as a reference, the acquisition delay time is shortened to 8μS which should be sufficient.

The Decide() assigns the ADC result value, shifted three bit positions to the left, to the TMR0_preload variable.

The Do_Outputs() assigns the current toggle bit value to RC0 that will transition the output accordingly.

Finally, the Timing() clears the TMR0 overflow flag (T0IF), preloads the TMR0 register with the TMR0_preload value subtracted from 255. The function then waits until the T0IF is set high before returning to the main(). In this way, as the temperature at the thermistor increases, as will the frequency of the PWM.

5.2.4.2 PROCEDURE

Using the firmware developed in the previous lab, make the following changes:

1. Copy/paste the code in Example 5-8 into the top of the main firmware source file

under the heading labeled:

//----------------DATA MEMORY---------------

Note: Be sure to paste over the code from the previous lab.

EXAMPLE 5-8: GLOBAL VARIABLES USE IN ADC LAB 2

2. Copy/paste the code in Example 5-9 over the Initialize() code from the

previous lab:

PICDEMTM Lab Development Board User’s Gu ide

//Configure Port:

PORTB = 0; //Disable pin output driver (See TRIS register) TRISB4 = 1;

// Configure RB4 as analog pin as analog ANS10 = 1;

//Configure RC0, RC1, RC2 and RC3 as digital output PORTC = 0; TRISC0 = 0; ANS4 = 0;

//Configure Timer0 as follows:

//Select the FOSC/4 internal instruction clock //as the clock source for TMR0 T0CS = 0; //Increment TMR0 value on low-to-high transition //of the FOSC/4 T0SE = 0; //Assign the prescaler to TMR0 PSA = 1; //Configure the prescaler to increment TMR0 //at a rate of 1:16 PS0 = 1; PS1 = 1; PS2 = 0;

//Configure the ADC module: //Select ADC conversion clock Frc ADCS0 = 1; ADCS1 = 1; ADCS2 = 1;

//Configure voltage reference using VDD VCFG = 0;

//Select ADC input channel Pin 13 (RB4/AN10) CHS0 = 0; CHS1 = 1; CHS2 = 0; CHS3 = 1;

//Select result format left justified ADFM = 0;

//Turn on ADC module ADON = 1;

EXAMPLE 5-9: INITIALIZE CODE FOR ADC LAB 2

3. Copy/paste the code in Example 5-10 over the Get_Inputs() code from the

previous lab:

Analog-to-Digital Converter Peripheral Labs

unsigned char counter = 2;

//Give ADC hold capacitor time to charge //This works out to approximately 8uS

while(--counter > 0);

//Start conversion by setting the GO/DONE bit. GODONE = 1;

//Wait for ADC conversion to complete //Polling the GO/DONE bit // 0 = ADC completed // 1 = ADC in progress while(GODONE == 1);

//Shift the ADRESH result to the left //by three bit positions and assign to //TMR0_preload TMR0_preload = ADRESH<<3;

//XOR the toggle value with 1 toggle ^= 1;

//Assign the toggle value to RC0 pin RC0 = toggle;

//Clear the T0IF T0IF = 0;

//Subtract the TMR0_preload value from 255 and //then use to preload TMR0 TMR0 = 255 – TMR0_preload;

//Sit here and wait for TMR0 to overflow while (T0IF == 0);

EXAMPLE 5-10: GET_INPUTS() CODE FOR ADC LAB 2

4. Copy/paste the code in Example 5-11 over the Decide() code from the previ-

ous lab:

EXAMPLE 5-11: DECIDE() CODE FOR ADC LAB 2

5. Copy/paste the code in Example 5-12 over the Do_Outputs() code from the

previous lab:

EXAMPLE 5-12: D0_OUTPUTS() CODE FOR ADC LAB 2

6. Copy/paste the code in Example 5-13 into the Timing() section labeled: //ADD TIMING CODE HERE

EXAMPLE 5-13: TIMING() CODE FOR ADC LAB 2

PICDEMTM Lab Development Board User’s Gu ide

Initialize(); //Initialize the relevant registers while(1) {

Get_Inputs(); Decide(); Do_Outputs(); Timing();

}

7. Copy/paste the code in Example 5-14 over the main() code from the previous

lab:

EXAMPLE 5-14: MAIN() CODE FOR ADC LAB 2

8. Compile the project. There should be no errors.

5.2.4.3 TESTING THE APPLICATION

Program the PIC16F690. An audible tone should emit from the speaker. Pinching the thermistor should introduce body heat to the component thereby increasing the frequency of the speaker output. Colder temperature sources applied to the thermistor should reduce the speaker output frequency.

The solution for this project is located in the C:\PICDEM_Lab\ADC_Labs\ADC_Lab2\solution directory.

DJ005B

S1G

BAT

270Ω

PWR ON

0.1

1N4148WS

LM317MSTT3G

OUT

ADJ

330Ω

1N4148WS

PICkit™ Serial Header

C™

SPI

USART

_ _ _

+5V

GND

SDA

SCL

_ _ _

+5V

GND

SDI

SCK

SDO

+5V

GND

_ _ _

PICkit™ Serial

J11

Receptical

J15

VDDVPPGND

ICSPDAT

ICSPCLK

ICSP1

191817

8/14/20p MCU

RA5

RA4

RA3

RC5

RC4

RC3

RC6

RC7

RB7

RA0

RA1

RA2

RC0

RC1

RC2

RB4

RB5

RB6

0.1uF

10uF

CCW

3352T-1-102

2PHDR

C10

15pF

C11

15pF

32 kHz

BT1

J26

2PHDR

BAT

J14

CDMG13008L-02-ND

J19

LS1

J10

0.1uF

GP2/T0CKI/COUT/FOSC4

GP1/ICSPCLK/CIN-

BP3/MCLR/V

GP0/ICSPDAT/CIN+5

PIC10F204_206-I_P

234

345

J18

ICSP3

J13

GND

ICSPDAT

ICSPCLK

J17

PIC_18P

RA2

RA3

RA4/TOCKI

MCLR

Vss

RB0/INT

RB1

RB2

RB3

RA1

RA0

OSC1/CLKIN

OSC2/CLKOUT

RB7

RB6

RB5

RB4

171615

141312

0.1uF

123

J16

ICSP2

J12

123

GND

ICSPDAT

ICSPCLK

ICSPDAT3

ICSPCLK3

ICSPDAT3

ICSPCLK3

GP2-U5

VDD1

ICSPDAT1

ICSPCLK1

RA2/RB2

RC0

RC1

RC2

RB4

RB5

RB6

RA5/RB5

RA4/RB4

RA3

RC5

RC4

RC3

RC6

RC7

RB7

ICSPDAT1

ICSPCLK1

SDO/RS

SCL/SCK

SDA/SDI

CS/TX

SP-

SP+

CP+

CN-

XT2

XT1

RB3

RB2

RB1

RB0

RA4

RA3

RA2

RA1

RA0

OSC1

OSC2

ICSPDAT2

ICSPCLK2

U3_RB5

U3_RB4

ICSPDAT2

ICSPCLK2

PICDEMTM LAB DEVELOPMENT

BOARD USER’S GUIDE

Appendix A. Schematic

A.1 PICDEM LAB DEVELOPMENT KIT SCHEMATIC

WORLDWIDE SALES AND SERVICE

AMERICAS

Corporate Office

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Tel: 86-29-8833-7252 Fax: 86-29-8833-7256

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Tel: 86-756-3210040 Fax: 86-756-3210049

ASIA/PACIFIC

India - Bangalore

Tel: 91-80-3090-4444 Fax: 91-80-3090-4080

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Thailand - Bangkok

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Austria - Wels

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Denmark - Copenhagen

Tel: 45-4450-2828 Fax: 45-4485-2829

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Tel: 33-1-69-53-63-20 Fax: 33-1-69-30-90-79

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Tel: 49-89-627-144-0 Fax: 49-89-627-144-44

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Tel: 39-0331-742611 Fax: 39-0331-466781

Netherlands - Drunen

Tel: 31-416-690399 Fax: 31-416-690340

Spain - Madrid

Tel: 34-91-708-08-90 Fax: 34-91-708-08-91

UK - Wokingham

Tel: 44-118-921-5869 Fax: 44-118-921-5820

02/04/09

Microchip Technology PICDEM™ Lab Development Board User’s Guide

Specifications and Main Features

Frequently Asked Questions

User Manual

1.1 INTRODUCTION

1.2 HIGHLIGHTS

Chapter 1. Overview

1.3 PICDEM™ LAB DEVELOPMENT KIT CONTENTS

1.4 PICDEM™ LAB DEVELOPMENT BOARD CONSTRUCTION AND LAYOUT

FIGURE 1-1: PICDEM™ LAB DEVELOPMENT BOARD

1.5 TARGET POWER

1.6 CONNECTING THE PICkit™ 2 PROGRAMMER/DEBUGGER

1.7 SOLDERLESS PROTOTYPING AREA STRIP CONFIGURATION

Chapter 2. Getting Started

2.1 INTRODUCTION

2.2 PREREQUISITES

2.3 THE SOFTWARE CONTROL LOOP

2.4 MPLAB® IDE DOWNLOAD INSTRUCTIONS

FIGURE 2-2: MPLAB ZIP FILE

FIGURE 2-3: HI TECH INSTALLER WINDOW

FIGURE 2-4: HI TECH LICENSE AGREEMENT

FIGURE 2-5: HI TECH COMPONENTS

FIGURE 2-6: HI TECH LANGUAGE PREFERENCES

FIGURE 2-7: HI TECH INSTALL CONFIRMATION

2.5 INSTALLING THE INCLUDED LAB FILES

Chapter 3. General Purpose Input/Output Labs

3.1 INTRODUCTION

3.2 GENERAL PURPOSE INPUT/OUTPUT LABS

3.3 GPIO OUTPUT LABS

3.3.1 Reference Documentation

3.3.2 Equipment Required for GPIO Output Labs

3.3.3 PICDEM Lab Development Board Setup for GPIO Output Labs

FIGURE 3-1: PICDEM LAB SCHEMATIC FOR GPIO OUTPUT LABS

3.3.4 Lab 1: Light LEDs

FIGURE 3-3: STEP ONE

FIGURE 3-4: STEP TWO

FIGURE 3-5: STEP THREE

FIGURE 3-6: STEP FOUR

FIGURE 3-7: SUMMARY

FIGURE 3-8: PROJECT WIN DOW

FIGURE 3-9: PICkit 2 PROGRAMMER/DEBUGGER TOOLBAR

FIGURE 3-10: LAB 1 LED OUTPUT

3.3.5 Lab 2: Flash LEDs (Delay Loop)

FIGURE 3-12: TIMING() DELAY ROUTINE FLOWCHART FOR LAB 2

3.3.6 Lab 3: Simple Delays Using Timer0

EQUATION 3-1: TMR0 OVERFLOW PERIOD USING FOSC/4

FIGURE 3-13: DELAY_10MS() USING TIMER0

EQUATION 3-4: MAXIMUM TMR0 OVERFLOW PERIOD

FIGURE 3-14: DELAY_1S() USING TIMER0

3.3.7 Lab 4: Rotate LEDs

FIGURE 3-16: DECIDE() FLOWCHART FOR LAB 4

FIGURE 3-17: RESULTS OF DO_OUTPUT()

3.4 GPIO INPUT LABS

3.4.1 Reference Documentation

3.4.2 Equipment Required for GPIO Input Labs

3.4.3 PICDEM Lab Development Board Setup for GPIO Input Labs

FIGURE 3-18: PICDEM LAB SCHEMATIC FOR GPIO INPUT LABS

3.4.4 Lab 5: Adding a Push Button

FIGURE 3-20: GET_INPUTS() SOFTWARE FLOWCHART FOR LAB 5

FIGURE 3-21: DELAY_5MS() SOFTWARE FLOWCHART FOR LAB 5

FIGURE 3-22: DECIDE() SOFTWARE FLOWCHART FOR LAB 5

3.4.5 Lab 6: Push Button Interrupt

FIGURE 3-24: PB_PRESSISR() FOR LAB 6 SHOWING SWITCH DEBOUNCE

3.4.6 Lab 7: Push Button Interrupt-on-Change

FIGURE 3-25: PB_PRESSISR FLOWCHART FOR LAB 7

3.4.7 Lab 8: Using Weak Pull-Ups

Chapter 4. Comparator Peripheral Labs

4.1 INTRODUCTION

4.2 COMPARATOR LABS

4.2.1 Reference Documentation

4.2.2 Comparator Labs

4.2.3 Equipment Required

4.2.4 Lab 1: Simple Compare

FIGURE 4-1: SCHEMATIC FOR COMPARATOR LAB 1

4.2.5 Lab 2: Using the Comparator Voltage Reference

FIGURE 4-3: SCHEMATIC FOR COMPARATOR LAB 2

4.2.6 Lab 3: Higher Resolution Sensor Readings Using a Single Comparator

FIGURE 4-4: BASIC RELAXATION OSCILLATOR CIRCUIT

FIGURE 4-5: SCHEMATIC FOR COMPARATOR LAB 3

FIGURE 4-7: TMR0_ISR FLOWCHART FOR COMPARATOR LAB 3