Compiled Tips ‘N Tricks Guide - Digi-Key

[Pages:137]Compiled Tips `N Tricks Guide

? 2009 Microchip Technology Inc.

DS01146B

Note the following details of the code protection feature on Microchip devices: ? Microchip products meet the specification contained in their particular Microchip Data Sheet.

? Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the intended manner and under normal conditions.

? There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip's Data Sheets. Most likely, the person doing so is engaged in theft of intellectual property.

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

? Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not mean that we are guaranteeing the product as "unbreakable."

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in this publication regarding device applications and the like is provided only for your convenience and may be superseded by updates.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, KEELOQ, 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, Hampshire, 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, , dsPICworks, dsSPEAK, ECAN, ECONOMONITOR, FanSense, In-Circuit Serial Programming, ICSP, ICEPIC, Mindi, MiWi, MPASM, MPLAB Certified logo, MPLIB, MPLINK, mTouch, nanoWatt XLP, PICkit, PICDEM, , PICtail, PIC32 logo, PowerCal, PowerInfo, PowerMate, PowerTool, REAL ICE, rfLAB, Select Mode, Total Endurance, TSHARC, 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.

? 2009, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved.

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? MCUs and dsPIC? DSCs, KEELOQ? code hopping 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.

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? 2009 Microchip Technology Inc.

8-pin Flash PIC? Microcontroller Tips `n Tricks

Tips `n Tricks TABLE OF CONTENTS

8-pin Flash PIC? Microcontrollers Tips `n Tricks

TIPS `N TRICKS WITH HARDWARE TIP #1: Dual Speed RC Oscillator........................... 1-2 TIP #2: Input/Output Multiplexing............................ 1-2 TIP #3: Read Three States From One Pin.............. 1-3 TIP #4: Reading DIP Switches................................ 1-3 TIP #5: Scanning Many Keys With One Input......... 1-4 TIP #6: Scanning Many Keys and Wake-up

From Sleep................................................. 1-4 TIP #7: 8x8 Keyboard with 1 Input.......................... 1-5 TIP #8: One Pin Power/Data................................... 1-5 TIP #9: Decode Keys and ID Settings..................... 1-6 TIP #10: Generating High Voltages........................... 1-6 TIP #11: Vdd Self Starting Circuit.............................. 1-7 TIP #12: Using PIC? MCU A/D For Smart

Current Limiter............................................ 1-7 TIP #13: Reading A Sensor With Higher Accuracy.... 1-8 TIP #13.1: Reading A Sensor With Higher

Accuracy ? RC Timing Method................... 1-8 TIP #13.2: Reading A Sensor With Higher

Accuracy ? Charge Balancing Method.......1-10 TIP #13.3: Reading A Sensor With Higher

Accuracy ? A/D Method..............................1-11 TIP #14: Delta Sigma Converter................................1-11

TIPS `N TRICKS WITH SOFTWARE TIP #15: Delay Techniques........................................1-12 TIP #16: Optimizing Destinations..............................1-13 TIP #17: Conditional Bit Set/Clear.............................1-13 TIP #18: Swap File Register with W..........................1-14 TIP #19: Bit Shifting Using Carry Bit..........................1-14

PIC? Microcontroller Low Power Tips `n Tricks

GENERAL LOW POWER TIPS `N TRICKS TIP #1 Switching Off External Circuits/

Duty Cycle................................................... 2-2

TIP #2 Power Budgeting........................................ 2-3

TIP #3 Configuring Port Pins.................................. 2-4

TIP #4 Use High-Value Pull-Up Resistors.............. 2-4

TIP #5 Reduce Operating Voltage.......................... 2-4

TIP #6 TIP #7

Use an External Source for CPU Core Voltage...................................... 2-5 Battery Backup for PIC MCUs ................... 2-6

DYNAMIC OPERATION TIPS `N TRICKS TIP #8 Enhanced PIC16 Mid-Range Core............. 2-6 TIP #9 Two-Speed Start-Up................................... 2-7 TIP #10 Clock Switching........................................... 2-7 TIP #11 Use Internal RC Oscillators......................... 2-7 TIP #12 Internal Oscillator Calibration...................... 2-8 TIP #13 Idle and Doze Modes.................................. 2-8 TIP #14 Use NOP and Idle Mode.............................. 2-9 TIP #15 Peripheral Module Disable

(PMD) Bits................................................... 2-9

? 2009 Microchip Technology Inc.

STATIC POWER REDUCTION TIPS `N TRICKS TIP #16 Deep Sleep Mode.......................................2-10 TIP #17 Extended WDT and Deep

Sleep WDT..................................................2-10 TIP #18 Low Power Timer1 Oscillator and RTCC....2-10 TIP #19 Low Power Timer1 Oscillator Layout..........2-11 TIP #20 Use LVD to Detect Low Battery..................2-11 TIP #21 Use Peripheral FIFO and DMA...................2-11 TIP #22 Ultra Low-Power

Wake-Up Peripheral....................................2-12

PIC? Microcontroller CCP and ECCP Tips `n Tricks

CAPTURE TIPS `N TRICKS TIP #1: Measuring the Period of a Square Wave.... 3-3 TIP #2: Measuring the Period of a

Square Wave with Averaging...................... 3-3 TIP #3: Measuring Pulse Width............................... 3-4 TIP #4: Measuring Duty Cycle................................. 3-4 TIP #5: Measuring RPM Using an Encoder............ 3-5 TIP #6: Measuring the Period of an Analog Signal.. 3-6 COMPARE TIPS `N TRICKS TIP #7: Periodic Interrupts....................................... 3-8 TIP #8: Modulation Formats.................................... 3-9 TIP #9: Generating the Time Tick for a RTOS.........3-10 TIP #10: 16-Bit Resolution PWM...............................3-10 TIP #11: Sequential ADC Reader..............................3-11 TIP #12: Repetitive Phase Shifted Sampling............3-12 PWM TIPS `N TRICKS TIP #13: Deciding on PWM Frequency.....................3-14 TIP #14: Unidirectional Brushed DC

Motor Control Using CCP...........................3-14 TIP #15: Bidirectional Brushed DC

Motor Control Using ECCP.........................3-15 TIP #16: Generating an Analog Output.....................3-16 TIP #17: Boost Power Supply...................................3-17 TIP #18: Varying LED Intensity..................................3-18 TIP #19: Generating X-10 Carrier Frequency...........3-18 COMBINATION CAPTURE AND COMPARE TIPS TIP #20: RS-232 Auto-baud......................................3-19 TIP #21: Dual-Slope Analog-to-Digital Converter......3-21

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Tips `n Tricks Table of Contents

PIC? Microcontroller Comparator Tips `n Tricks

TIP #1: TIP #2: TIP #3: TIP #4: TIP #5: TIP #6: TIP #7: TIP #8: TIP #9: TIP #10: TIP #11: TIP #12: TIP #13: TIP #14: TIP #15:

Low Battery Detection................................. 4-2 Faster Code for Detecting Change............. 4-3 Hysteresis................................................... 4-4 Pulse Width Measurement.......................... 4-5 Window Comparison................................... 4-6 Data Slicer.................................................. 4-7 One-Shot..................................................... 4-8 Multi-Vibrator (Square Wave Output).......... 4-9 Multi-Vibrator (Ramp Wave Output)............4-10 Capacitive Voltage Doubler........................4-11 PWM Generator..........................................4-12 Making an Op Amp Out of a Comparator...4-13 PWM High-Current Driver...........................4-14 Delta-Sigma ADC........................................4-15 Level Shifter................................................4-16

TIP #16: TIP #17: TIP #18: TIP #19: TIP #20:

Logic: Inverter.............................................4-16 Logic: AND/NAND Gate..............................4-17 Logic: OR/NOR Gate..................................4-18 Logic: XOR/XNOR Gate.............................4-19 Logic: Set/Reset Flip Flop...........................4-20

PIC? Microcontroller DC Motor Control Tips `n Tricks

TIP #1: TIP #2: TIP #3: TIP #4: TIP #5:

TIP #6: TIP #7:

Brushed DC Motor Drive Circuits................ 5-2 Brushless DC Motor Drive Circuits............. 5-3 Stepper Motor Drive Circuits....................... 5-4 Drive Software............................................ 5-6 Writing a PWM Value to the CCP Registers with a Mid-Range PIC? MCU...... 5-7 Current Sensing.......................................... 5-8 Position/Speed Sensing.............................. 5-9

Application Note References..........................................5-11

Motor Control Development Tools..................................5-11

LCD PIC? Microcontroller Tips `n Tricks

TIP #1:

TIP #2: TIP #3: TIP #4: TIP #5:

TIP #6:

TIP #7: TIP #8: TIP #9: TIP #10:

TIP #11: TIP #12:

Typical Ordering Considerations and Procedures for Custom Liquid Displays...... 6-2 LCD PIC? MCU Segment/Pixel Table......... 6-2 Resistor Ladder for Low Current................. 6-3 Contrast Control with a Buck Regulator...... 6-5 Contrast Control Using a Boost Regulator.................................................... 6-5 Software Controlled Contrast with PWM for LCD Contrast Control................... 6-6 Driving Common Backlights........................ 6-7 In-Circuit Debug (ICD)................................ 6-8 LCD in Sleep Mode..................................... 6-8 How to Update LCD Data Through Firmware....................................... 6-9 Blinking LCD............................................... 6-9 4 x 4 Keypad Interface that Conserves Pins for LCD Segment Drivers....................6-10

Application Note References..........................................6-11

Intelligent Power Supply Design Tips `n Tricks

TIP #1: TIP #2: TIP #3:

TIP #4: TIP #5:

TIP #6: TIP #7:

TIP #8: TIP #9:

TIP #10: TIP #11:

TIP #12: TIP #13: TIP #14: TIP #15:

TIP #16:

TIP #17: TIP #18: TIP #19:

TIP #20: TIP #21:

Soft-Start Using a PIC10F200.................... 7-2 A Start-Up Sequencer................................. 7-3 A Tracking and Proportional Soft-Start of Two Power Supplies............... 7-4 Creating a Dithered PWM Clock................. 7-5 Using a PIC? Microcontroller as a Clock Source for a SMPS PWM Generator.......... 7-6 Current Limiting Using the MCP1630......... 7-7 Using a PIC? Microcontroller for Power Factor Correction............................. 7-8 Transformerless Power Supplies................ 7-9 An IR Remote Control Actuated AC Switch for Linear Power Supply Designs....7-10 Driving High Side FETs...............................7-11 Generating a Reference Voltage with a PWM Output...............................................7-12 Using Auto-Shutdown CCP.........................7-13 Generating a Two-Phase Control Signal.....7-14 Brushless DC Fan Speed Control...............7-15 High Current Delta-Sigma Based Current Measurement Using a Slotted Ferrite and Hall Effect Device.................................7-16 Implementing a PID Feedback Control in a PIC12F683-Based SMPS Design........7-17 An Error Detection and Restart Controller..7-18 Data-Indexed Software State Machine.......7-19 Execution Indexed Software State Machine.............................................7-20 Compensating Sensors Digitally.................7-21 Using Output Voltage Monitoring to Create a Self-Calibration Function..............7-22

3V Tips `n Tricks

TIP #1:

TIP #2:

TIP #3:

TIP #4:

TIP #5: TIP #6: TIP #7: TIP #8: TIP #9: TIP #10: TIP #11: TIP #12: TIP #13: TIP #14: TIP #15: TIP #16: TIP #17: TIP #18: TIP #19:

Powering 3.3V Systems From 5V Using an LDO Regulator............................. 8-3 Low-Cost Alternative Power System Using a Zener Diode................................... 8-4 Lower Cost Alternative Power System Using 3 Rectifier Diodes............................. 8-4 Powering 3.3V Systems From 5V Using Switching Regulators........................ 8-5 3.3V 5V Direct Connect.......................... 8-6 3.3V 5V Using a MOSFET Translator.... 8-6 3.3V 5V Using A Diode Offset................ 8-7 3.3V 5V Using A Voltage Comparator.... 8-8 5V 3.3V Direct Connect.......................... 8-9 5V 3.3V With Diode Clamp.................... 8-9 5V 3.3V Active Clamp............................8-10 5V 3.3V Resistor Divider........................8-10 3.3V 5V Level Translators......................8-12 3.3V 5V Analog Gain Block....................8-13 3.3V 5V Analog Offset Block..................8-13 5V 3.3V Active Analog Attenuator..........8-14 5V 3V Analog Limiter..............................8-15 Driving Bipolar Transistors..........................8-16 Driving N-Channel MOSFET Transistors....8-18

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? 2009 Microchip Technology Inc.

8-pin Flash PIC? Microcontroller Tips `n Tricks

CHAPTER 1 8-Pin Flash PIC? Microcontrollers

Tips `n Tricks

Table Of Contents

TIPS `N TRICKS WITH HARDWARE

TIP #1: Dual Speed RC Oscillator................. 1-2

TIP #2: Input/Output Multiplexing.................. 1-2

TIP #3: Read Three States From One Pin.... 1-3

TIP #4: Reading DIP Switches...................... 1-3

TIP #5:

Scanning Many Keys With One Input.......................................... 1-4

TIP #6:

Scanning Many Keys and Wake-up From Sleep....................................... 1-4

TIP #7: 8x8 Keyboard with 1 Input................ 1-5

TIP #8: One Pin Power/Data......................... 1-5

TIP #9: Decode Keys and ID Settings........... 1-6

TIP #10: Generating High Voltages................. 1-6

TIP #11: Vdd Self Starting Circuit.................... 1-7

TIP #12: Using PIC? MCU A/D For Smart Current Limiter.................................. 1-7

TIP #13: Reading A Sensor With Higher Accuracy........................................... 1-8

TIP #13.1: Reading A Sensor With Higher Accuracy ? RC Timing Method......... 1-8

TIP #13.2: Reading A Sensor With Higher Accuracy ? Charge Balancing Method.............................................. 1-10

TIP #13.3: Reading A Sensor With Higher Accuracy ? A/D Method.................... 1-11

TIP #14: Delta Sigma Converter...................... 1-11

TIPS `N TRICKS WITH SOFTWARE

TIP #15: Delay Techniques.............................. 1-12 TIP #16: Optimizing Destinations.................... 1-13 TIP #17: Conditional Bit Set/Clear................... 1-13 TIP #18: Swap File Register with W................ 1-14 TIP #19: Bit Shifting Using Carry Bit................ 1-14

TIPS `N TRICKS INTRODUCTION

Microchip continues to provide innovative products that are smaller, faster, easier to use and more reliable. The 8-pin Flash PIC? microcontrollers (MCU) are used in an wide range of everyday products, from toothbrushes, hair dryers and rice cookers to industrial, automotive and medical products.

The PIC12F629/675 MCUs merge all the advantages of the PIC MCU architecture and the flexibility of Flash program memory into an 8-pin package. They provide the features and intelligence not previously available due to cost and board space limitations. Features include a 14-bit instruction set, small footprint package, a wide operating voltage of 2.0 to 5.5 volts, an internal programmable 4 MHz oscillator, on-board EEPROM data memory, on-chip voltage reference and up to 4 channels of 10-bit A/D. The flexibility of Flash and an excellent development tool suite, including a low-cost In-Circuit Debugger, In-Circuit Serial ProgrammingTM and MPLAB? ICE 2000 emulation, make these devices ideal for just about any embedded control application.

TIPS `N TRICKS WITH HARDWARE

The following series of Tips 'n Tricks can be applied to a variety of applications to help make the most of the 8-pin dynamics.

? 2009 Microchip Technology Inc.

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8-pin Flash PIC? Microcontroller Tips `n Tricks

TIP #1 Dual Speed RC Oscillator

Figure 1-1

+5V PIC12F6XX

R1 R2 GP0

OSC1 C

1. After reset I/O pin is High-Z 2. Output `1' on I/O pin 3. R1, R2 and C determine OSC frequency 4. Also works with additional capacitors Frequency of PIC MCU in external RC oscillator mode depends on resistance and capacitance on OSC1 pin. Resistance is changed by the output voltage on GP0. GP0 output `1' puts R2 in parallel with R1 reduces OSC1 resistance and increases OSC1 frequency. GP0 as an input increases the OSC1 resistance by minimizing current flow through R2, and decreases frequency and power consumption.

Summary: GP0 = Input: Slow speed for low current GP0 = Output high: High speed for fast

processing

TIP #2 Input/Output Multiplexing

Individual diodes and some combination of diodes can be enabled by driving I/Os high and low or switching to inputs (Z). The number of diodes (D) that can be controlled depends on the number of I/Os (GP) used.

The equation is: D = GP x (GP - 1).

Example 2-1: Six LEDs on Three I/O Pins

GPx

LEDs

012 123456

0 0 0 0 1 Z 1 0 Z Z 0 1 Z 1 0 0 Z 1 1 Z 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1

0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 1 0 1 0 1 0 0 1 0 0 1 0 0 0 1 0 0 1 0 0 0 1 0 1 1 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0

Figure 2-1

PIC12F6XX

GP0 GP1

GP2

12 34

56

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8-pin Flash PIC? Microcontroller Tips `n Tricks

TIP #3 Read Three States From One Pin

To check state Z: ? Drive output pin high ? Set to Input ? Read 1 ? Drive output pin low ? Set to Input ? Read 0

Figure 3-1

PIC I/O

To check state 0: ? Read 0 on pin

To check state 1: ? Read 1 on pin

5V Link 1

Link 0 0V

State 0 1 NC

Link 0 closed open open

Link 1 open closed open

Jumper has three possible states: not connected, Link 1 and Link 0. The capacitor will charge and discharge depending on the I/O output voltage allowing the "not connected" state. Software should check the "not connected" state first by driving I/O high, reading 1 and driving I/O low and reading 0. The "Link 1" and "Link 0" states are read directly.

TIP #4 Reading DIP Switches

The input of a timer Example 4-1

can be used to test

which switch(s)

movlw movwf

is closed. The input of Timer1 is

movwf movlw movwf

held high with a

movlw movwf

pull-up resistor. Sequentially,

LOOP

clrf clrf

each switch I/O is

movf movwf

set to input and Timer1 is checked

btfsc andwf bsf

for an increment

rlf btfsc

indicating the switch is closed.

goto retlw

b'11111111' TRISIO DIP b'00000111' T1CON b'11111110' Mask GPIO

TMR1L Mask,W TRISIO TMR1L,0 DIP,F STATUS,C Mask,F Mask,4 Loop 0

Each bit in the DP register represents its corresponding switch position. By setting Timer1 to FFFFh and enabling its interrupt, an increment will cause a rollover and generate an interrupt. This will simplify the software by eliminating the bit test on the TMR1L register.

Sequentially set each GPIO to an input and test for TMR1 increment (or 0 if standard I/O pin is used).

Figure 4-1

PIC12F6XX GP5/T1CKI

VDD 10K

Data I/O

GP4

GP3 GP2 GP1 GP0

? 2009 Microchip Technology Inc.

DS01146B-Page 1-3

8-pin Flash PIC? Microcontroller Tips `n Tricks

TIP #5 Scanning Many Keys With One Input

The time required to charge a capacitor depends on resistance between Vdd and capacitor. When a button is pressed, Vdd is supplied to a different point in the resistor ladder. The resistance between Vdd and the capacitor is reduced, which reduces the charge time of the capacitor. A timer is used with a comparator or changing digital input to measure the capacitor charge time. The charge time is used to determine which button is pressed.

Software sequence:

1. Configure GP2 to output a low voltage to discharge capacitor through I/O resistor.

2. Configure GP2 as one comparator input and CVref as the other.

3. Use a timer to measure when the comparator trips. If the time measured is greater than the maximum allowed time, then repeat; otherwise determine which button is pressed.

When a key is pressed, the voltage divider network changes the RC ramp rate.

Figure 5-1

TIP #6 Scanning Many Keys and Wake-up From Sleep

An additional I/O can be added to wake the part when a button is pressed. Prior to Sleep, configure GP1 as an input with interrupt-onchange enabled and GP2 to output high. The pull-down resistor holds GP1 low until a button is pressed. GP1 is then pulled high via GP2 and Vdd generating an interrupt. After wake-up, GP2 is configured to output low to discharge the capacitor through the 220 resistor. GP1 is set to output high and GP2 is set to an input to measure the capacitor charge time.

? GP1 pin connected to key common ? Enable wake-up on port change ? Set GP1 as input and GP2 high prior to Sleep ? If key is pressed the PIC MCU wakes up, GP2

must be set low to discharge capacitor ? Set GP1 high upon wake-up to scan keystroke

Figure 6-1

VDD 100R

R

R

R

16 Resistors

PIC12F6XX

GP5 GP4 GP3

GP0 GP1 GP2

R 220 R

16 R Resistors

PIC12F6XX

GP5 GP4 GP3

GP0 GP1 GP2

R

R 220

See AN512, "Implementing Ohmmeter/ Temperature Sensor" for code ideas.

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