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TRAINING MANUAL
Single-slope PWM Implementation using SAM D21 TCC in
a Touch- based Application
AN- 9232
Prerequisites
• Hardware Prerequisites
• Atmel® SAM D21 Xplained Pro Evaluation Kit
• Atmel KitQT1 Xplained Pro
• USB Micro Cable (TypeA/ -B) Micro
• Software Prerequisites
• Atmel Studio 6.2 or higher
• Atmel Software Framework 3.1 .0 or higher7
• Atmel QTouch® Composer 5.3 or higher
• Atmel QTouch Library 5.3 or higher
• Documentation Prerequisites
• Atmel- - - - - - - -42271 Introduction to QTouch Design Parameters using
SAM- - - - -D21 Xplained Pro_Training Manual_AN 7846 Training Manual
• Estimated completion time: 60min.
Introduction
The goal of this hands on is to:-
• Create a Touch proje using QTouch Project Builderct
• Use QTouch Analyzer to test the project
• Implement a PWM signal using the SAM D21 Timer/Counters for Control
peripheral the brightness (TCC) to drive of a LED
• Modify the utton LED brightness in relation to the Touch Delta value of a B
sensor by updating the PWM duty cycle
42327 A 07/−2014
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Table of Contents
Prerequisites .....................................................................................1
Introduction .......................................................................................1
Icon Key Identifiers ...........................................................................3
1. Training Module Architecture .....................................................4
1.1 Atmel Studio Extension (.vsix) ............................................................. 4
1.2 Atmel Training Executable (.exe) ......................................................... 4
2. Introduction ................................................................................5
3. Assignment 1: Create a Touch project using QTouch Project
Builder ........................................................................................6
3.1 Project Creation ................................................................................... 6
3.2 Conclusion ......................................................................................... 18
4. Assignment 2: Use QTouch Analyzer to Test the Project ........ 19
4.1 Connect the Kit to QTouch Analyzer ................................................. 19
4.2 Test the Proximity Effect of the QTouch Application ......................... 23
4.3 Conclusion ......................................................................................... 24
5. Assignment 3: Implement a PWM Signal using the SAM D21
Timer/Counters for Control Application Peripheral (TCC) ........ 25
5.1 Introduction to Timer/Counters for Control Application (TCC) ........... 25
5.2 TCC Peripheral Initialization Using ASF Quick Start Guide. ............. 27
5.3 Conclusion ......................................................................................... 34
6. Assignment 4: Use QTouch Button to Control LED Brightness 35
6.1 Reading and using Button Touch Delta Value ................................... 35
6.2 Using PWM to Control LED Brightness ............................................. 37
6.3 Conclusion ......................................................................................... 41
7. Conclusion ............................................................................... 42
8. Revision History ....................................................................... 43
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Icon Key Identifiers
Delivers contextual information about a specific topic.
Highlights useful tips and techniques.
Highlights objectives to be completed.
Highlights the expected result of an assignment step.
Indicates important information.
Highlights actions to be executed out of the target when
necessary.
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1. Training Module Architecture
This training material can be retrieved through different Atmel deliveries:
• As an Atmel Studio Extension ( file) usually found on the Atmel Gallery web site .vsix
( http://gallery.atmel.com/) or using the Atmel Studio Extension manager
• As an Atmel Training Executable ( file) usually provided during Atmel Training sessions.exe
Depending on the delivery type, the different resources needed by this training material (hands-on
documentation, datasheets, application notes, software, and tools) will be found on different locations.
1.1 Atmel Studio Extension (.vsix)
Once the extension installed, you can open and create the different projects using “New Example Project
from ASF..." in Atmel Studio.
The projects installed from an extension are usually under “Atmel Training >
Atmel Corp. Extension Name” .
There are different projects which can be available depending on the extension:
• Hands-on Documentation: contains the documentation as required resources
• Hands-on Assignment: contains the initial project that may be required to start
• Hands-on Solution: contains the final application which is a solution for this hands- on
Each time a reference is made to some resources in the following pages, the user
must refer to the project folderHands-on Documentation .
1.2 Atmel Training Executable (.exe)
Depending where the executable has been installed, you will find the following architecture which is
composed by two main folders:
• AN XXXX_Hands on- - : contains the initial project that may be required to start and a solution
• Resources: contains required resources (datasheets, software, and tools…)
Unless a specific location is specified, each time a reference is made to some
resources in the following pages, the user must refer to this Resources folder.
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2. Introduction
This hands-on will focus on the development of a simple Touch application that uses a Button sensor from the
Atmel QT1 Xplained Pro Self Capacitance extension board to modify the brightness of a LED.
The LED brightness is controlled using a PWM signal that is generated by one of the Atmel SAM D21
Timer/Counters for Control (TCC) peripherals.
The SAM D21 embeds three different 24 bit Timer/Counters for Control peripherals which provide extended -
functions compared to the standard Timer/Counters (TC):
• Up to four compare channels with optional complementary outputs
• Advanced waveform signal generation with dead time management
• Deterministic fault protection, fast decay, and configurable dead time between complementary -
outputs
• Dithering that increase resolution with up to five bits and reduce quantization error
The hands on will be divided in the following assignments:-
• Create a new Touch project based on BUTTON 1 Touch sensor using QTouch lder from Project Bui
Atmel QTouch Composer:
• Use QTouch Analyzer to provide graphical representation and demonstration of real time touch
data the . This will allow testing newly- . created Touch project
• Implement a PWM signal using the TCC0 to control the LED8 brightnessperipheral
• Atmel Software Framework TCC Quick Start Guide will be used to implement it (ASF)
easily
• A Waveform Output pin (WO6) from the SAM D21 MCU will be used to output the PWM
signal directly to the LED8
• Modify of the LED brightness in relation to the Touch Delta value BUTTON 1 by updating the PWM
duty cycle
• Atmel QTouch library API will be used to get the delta value of BUTTON 1 sensor
BUTTON 1
LED8
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3. Assignment 1: Create a Touch project using QTouch Project Builder
3.1 Project Creation
Create a new QTouch Project.
• Open Atmel Studio 6.2
• Click on the “QT” icon to open the QTouch Start Page :
QTouch StartPage is also accessible through the Tools menu:
• Select “New QTouch UserBoard Project…”
• Ensure “GCC QTouch Executable Project” is selected (default)*
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• Fill- in New Project fields according to following use cases:
Atmel Training Executable Case
• Name: Hands On Assignment-
• Location: “AN- - \ 9232_SAMD21 XPRO_QTouch_TCC assignments”
(relative path in the installation folder)ATMEL_TRAINING
• Solution name: - Hands On Assignment
• Click OK
Atmel Extension Case (downloaded from Atmel Gallery or Studio Extension Manager)
• Name: Hands On Assignment-
• Location: existing on Documentation Hands- solution path
• Solution name: - Hands On Documentation
• Click OK
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The QTouch Project Builder wizard will guide through the steps involved in creating a QTouch projectnow .
• Click “Next” in the Getting Started page (if shown):
The Kit design Page provides option to add, delete move QTouch Sensors such as button, wheel and an or
slider. also It provides options to setup physical and firmware properties of the board and sensors.
• Add a button in the page by clicking on the “Button” icon, click “Add” and “Next”Kit Design
1
2
3
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The technology Technology Selection Guide recommends which acquisition should be used based on the
number of sensors selected in Kit Design page and answers the below questionnairepreviously from .
• We will consider for this hands on that our application hardware design exposed to moisture - is NOT
or water droplets or any specific sources of radiated noises
So, select “ ” as the answer to Question 1 . You will see that the proposed technology will No and 2
become QTouch ( i.e. Self Capacitance Technology):
For more information about designing the touch sensor, refer to Buttons, Sliders and
Wheels Touch Sensor Design Guide available at
www.atmel.com/images/doc10752.pdf.
• Click “Next” in the Guide for Selecting Touch Technology page
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Device Selection Page provides the option to view the number of QTouch sensors such as Button, Wheel and
Slider that was selected in the Kit Design Page.
Touch sensors can be based on two sub-technologies, QTouch/Self Capacitance and QMatrix/Mutual
Capacitance.
• We can verify that has been correctly selected following our previous QTouch/ Self Capacitance
choice in the Guide for Selecting Touch Technology page
The device list displays device details such as Device Name, Variant, Application/Boot Memory, Data
Memory, EEPROM and supported technology. Data listing will vary based on device family, number of
selected sensors and technology as only devices supporting all choices made will be shown. Additionally user
has the option to search for a particular device.
• Type “SAMD21” in the searc box to make a first filteringh
• Select ATSAMD21J18A in the page and click “Next”. This is the device on the SAM Select Device
D21 Xplained Pro kit.
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Self capacitance method uses a single sense electrode, denoted by a Y line.
Self capacitance touch button sensor is formed using a single Y line channel, while a touch rotor or slider
sensor can be formed using three Y line channels.
The Y-line numbering in the QT1 Xplained Pro User Guide does not correspond to
the Y-line numbering in the SAM D21 PTC module as the QT1 Xplained Pro is a
generic touch board (not dedicated to the SAM D21).
• Flip the SAM D21 Xplained Pro and QT1 Xplained Pro boards and determine which SAM D21 I/O
pins that are connected to BUTTON 1
Look at next page to determine the right Y-line from QT1 Xplained PRO extension
board.
QT1
X plained PRO
SAM D21
Xplained PRO
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Y- line for BUTTON 1 can be retrieved from the Atmel QT1 Xplained Pro User Guide
( http://www.atmel.com/Images/Atmel- - - - -42193 QT1 Xplained Pro_User Guide.pdf):
Table 3- 1. QT1 Xplained Pro SC Extension Header 1
Pin on EXT Function Description
1 ID Communication line to ID chip.
2 GND Ground
3 Y-Y_1 line 1 for Slider
4 Y-Y_2 line 2 for Slider
5 Y-Y_3 line 3 for Slider
6 Y-Y_4 line 4 for Wheel
7 LED_0 Slider, LED 0 (Yellow)
8 LED_1 Slider, LED 1 (Yellow)
9 Y-Y_5 line 5 for Wheel
10 Y-Y_6 line 6 for Wheel
11 Connected Not
12 Not Connected
13 Not Connected
14 Not Connected
15 LED_2 Slider, LED 2 (Yellow)
16 Y-Y_7 line 7 for Button 2
17 LED_3 Slider, LED 3 (Yellow)
18 Y-Y_8 line 8 for Button 1
19 Ground GND
20 VCC Target supply voltage
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• Use the page from QTouch Project Builder to select the Assign X-Y Line and Gain to the Channel
correct Y Line:
Y Line QT1 Xplained PRO
Y Line
SAM D21 Xplained PRO
Y Line – I/O
Y- – PA07 line Y_8 Y[5]
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We also need to select on this page the for eachGain channel.
Gain setting -is applied on a per channel basis to allow superior sensitivity upon
contact. Recommended gain settings depend on the sensor design and touch panel
thickness.
The increase in the gain value is usually required by a thick front panel but also
depends on the sensor design (size of the sensor and coupling between X and Y for
mutual capacitance sensors).
Thicker front panels (3mm and more) can result in reduced sensitivity upon touch.
Likewise, smaller size sensors or sensors surrounded by ground layer or sensors
with ground on the bottom side typically require an increased gain setting.
• In this application, we need to increase the sensor sensitivity to get the highest proximity effect
possible
As a consequence, set Gain to and click 32 “Next”.
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• Check the “Enable QDebug Interface” checkbox, which allows Live streaming of Touch data with
QTouch Analyzer
QDebug is the Touch data protocol used by QTouch Analyzer to communicate with
the SAM D21 through the Atmel nterface (Data Gateway I DGI).
The Atmel Embedded Debugger ( ) offers a Data Gateway Interface (EDBG DGI) for
streaming data to a host PC. This is meant as an aid in debugging and
demonstration of features in the application running on the target device. DGI
consists of multiple interfaces for data streaming. The supported interfaces are SPI
Interface, USART Interface, TWI Interface, and GPIO Interface.
SAM D21 G XPRO Kit Data ateway Interface supports SPI or I²C.
• A 1 ssign the right port(s) and pins to the SPI interface, these can be found in the SAM D2 Xplained
Pro U G (ser uide on the pageAdvanced Options http://www.atmel.com/Images/Atmel- -42220
SAMD21-Xplained- -Pro_User Guide.pdf):
Table 3- 2. DGI Interface Connections when Using SPI
Pin on SAM D21 Function
PB31 SERCOM5 PAD[1] SPI SS (Slave select) (SAM D21 is Master)
PB16 SERCOM5 PAD[0] SPI MISO (Master In, Slave Out)
PB22 SERCOM5 PAD[2] SPI MOSI (Master Out, Slave In)
PB23 SERCOM5 PAD[3] SPI SCK (Clock Out)
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The following table extracted from the QTouch Library PTC User Guide (http://www.atmel.com/Images/Atmel-
42195 Qtouch Library Peripher Touch Controller_User Guide.pdf- - - al- - - ), indicates the expected Resting Signal
value (also called for a given combination of gain setting and filter level setting.Reference)
Expected Resting Signal
Value for FILTER LEVEL
and GAIN Combination GAIN_1=0 GAIN_2=1 GAIN_4=2 GAIN_8=3 GAIN_16=4 GAIN_32=5
FILER_LEVEL_1 = 0
512 512 512 512 512 512
FILER_LEVEL_2 = 1
512 1024 1024 1024 1024 1024
FILER_LEVEL_4 = 2
512 1024 2048 2048 2048 2048
FILER_LEVEL_8 = 3
512 1024 2048 4096 4096 4096
FILER_LEVEL_16 = 4
512 1024 2048 4096 8192 8192
FILER_LEVEL_32 = 5
512 1024 2048 4096 8192 16384
FILER_LEVEL_64 = 6
512 1024 2048 4096 8192 16384
By increasing both the Gain and the Filter Level, we will increase the Reference value and so scale up the
Touch Delta value will allow improving the proximity effect, which .
(Touch) Delta represents the difference between the Signal and the Reference.
• On the pdate Filter Level to on the Advanced Options page, u 64:
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• Review the Summary page which provides a summary of the settings provided by the previous set
of wizard pages. Then, click on Finish and wait for your Touch project to be generated.
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You have created a T B Touch Project with a Self Capacitance technology ouch utton.
3.2 Conclusion
In the first assignment, you have learnt:
• How to create a Touch Project using QTouch Composer Project Builder
• How easy it is to use QTouch Composer to design a Touch project on the Atmel SAM D21 MCUs
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4. Assignment 2: Use QTouch Analyzer to T the P est roject
4.1 Conne to ct the Kit QTouch Analyzer
Build t Q . he Touch project and Program the SAM D21 Xplained Pro
• Connect the QT1 Xplained Pro Capacitance board to the SAM D21 Xplained Pro board:Self
• Connect the SAM D21 Xplained Pro to your PCboard using DEBUG USB connector
• Build the solution and ensure you get no errors:
• Program the application by clicking on the Start Without Debugging icon:
DEBUG USB
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• You will be asked the first time to select your debug tool:
• Select your EDBG and SWD (Serial Wire Debug) as Interface:
• Set SWD clock to 8MHz to speed up programming:
• Click again on the Start Without Debugging icon:
You may be asked to upgrade your EDBG firmware. If so, click on Upgrade:
Upgrade operation may take a few minutes, please wait for the operation to
complete.
Your QTouch project is now updated and programmed on the SAM D21 Xplained
Pro.
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Connect your kit to QTouch Analyzer.
• Press RESET button on the SAM D21 Xplained Pro
• Launch QTouch Analyzer by clicking on the following icon:
QTouch Analyzer is also accessible through the Tools menu:
• A kit named QD _DGI will be listed in the combo box.EBUG
Select the kit and click on Connect:
• DGI settings dialog box will be displayed as shown in the figure, click OK:
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The Virtual kit will be displayed, which shows it has been correctly connected:
• Click on Start Reading:
QTouch Analyzer is now connected to your kit and displays both the sensor signal
and reference values.
C lick on Stop Reading to prevent QTouch Analyzer from collecting touch data over a
long period as this might slow down the computer.
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• Approach BUTTON 1 on your kit, which is displayed as Button0 on QTouch Analyzer and check
that a detect touch can occur BEFORE touching the sensor (i.e. the sensor Touch Delta value
becomes higher than Detect Threshold)its .
You can also check signal, reference and delta values as well as Touch Button state
by using the Tabular View instead of the Trace View:
You may in some cases, observe a detect touch even without approaching the finger.
This is due to the high gain . value which has been configured for that sensor The
highest the gain is, the highest sensitivity the sensor is.
The proximity effect of the Touch project behaves . as expected
4.3 Conclusion
In this assignment, you have learnt:
• How to use QTouch Analyzer to test a Touch application
Touch
Detected
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5. Assignment 3: Implement a PWM Signal using the SAM D21 Timer/Counters
for Control Application Peripheral (TCC)
In this assignment, a Pulse Width M- odulation (PWM) signal will be generated using the SAM D21
Timer/Counters for Control Application (TCC) QT1 Xplained Pro extension boardto the oflight LED8 :
5.1 Introduction to Timer/Counters for Control Application (TCC)
T - he TCC will be used in Single Slope PWM mode to generate the required PWM signal and output it on a
dedicated Waveform Output pin (WO[x]).
For single-slope PWM generation , the period time is controlled by , while the mode the Period register (PER)
Compare/Capture registers (CCx) control the duty cycle of the waveform.
When up-counting pin (default configuration), WO[x] is:
• S ) s et at start or compare match between the counter (COUNT and period (PER) registers’ value
• C ) ) leared on compare match between the counter (COUNT and Compare/Capture (CCx registers’
values
LED8
BUTTON 1
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Determine which Waveform Output pin . to use
• By flipping the boards, you can check that the LED8 of the QT1 Xplained Pro extension board is
connected to the SAM D21 Xplained Pro board pin PB12:
• By looking at the SAM D21 product datasheet, you can verify that thnow is is the Waveform Output
pin 6 [6] (WO ) from TCC0 which is multiplexed with PB12
Table 5 Function Multiplexing (Continued)- 1. PORT
Pin I/O Pin Supply A B C D E F G H Type
SAMD21E
SAMD21G
SAMD21J -EIC REF ADC AC PTC DAC SERCOM SERCOM ALT
TC/TCC TCC COM AC/GCLK
PB10 19 23 VDDIO EXTINT[10] SERCOM4
/PAD[2]
TC5/WO[0] TCC0/
WO[4]
I2S/
MCK[1]
GCLK_IO[4]
PB11 20 24 VDDIO EXTINT[11] SERCOM4
/PAD[3]
TC5/WO[1] TCC0/
WO[5]
I2S/
SCK[1}
GCLK_IO[5]
PB12 I25 VDDIO 2C EXTINT[12] X[12] SERCOM4/
PAD[0]
TC4/WO[0] TCC0/
WO[6]
I2S/
FS[1]
GCLK_IO[6]
SAM D21 Product Datasheet can be retrieved at the following link:
http://www.atmel.com/Images/Atmel- - -42181 SAM D21_Datasheet.pdf.
WO[6] pin must d . be use to output the PWM signal directly to LED8 using TCC0
QT1
X plained PRO
SAM D21
Xplained PRO
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5.2 Peripheral TCC Initialization Using ASF Quick Start Guide
The drivers in ASF have quick start guides as part of their API documentation.
Quick Start guides show and explain, in a step-by-step process, the code and actions needed to set up and
use a driver in one or more use cases.
Once a driver such as TCC is added using the ASF Wizard, its Quick Start Guide becomes available in the
ASF Explorer view.
To get started on the ASF API documentation as the Quick Start Guides, please go
to: http://asf.atmel.com/docs/latest/get_started.html.
Add TCC Support using ASF Wizard.
• Click on the ASF Wizard icon or r on the Hands on Assignment pright click - oject > ASF Wizard
• From latest ASF version available, s the following component and add it to the Selected elect
Modules (Add >> button):
• TCC – – Timer Counter for Control Applications (driver) polled
In this application, TCC polled driver version can be used as no interrupt(s)
management is required to generate the PWM signal on the waveform output WO[x]
pin.
• Click on Apply button
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• Click on Solution Explorer tab and check that the TCC driver has been successfully added as
shown below:
TCC driver is added to the project.
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The following code that will be implemented can be found the sub section of the Quick Start Guide called in
Workflow.
That sub section provides a detailed step by step the TCC in a “polled mode” useguide to initialize :
TCC Initialization Implementation.
• In the main.c file, ate a new function above main functioncre ( in red):
static void configure_tcc(void)
{
}
int main (void)
{
s ystem_init();
• Create a TCC module instance:
struct tcc_module tcc_instance ;
static void configure_tcc(void)
{
}
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• In the reate a TCC module configuration configure_tcc function, c instance and initialize it with
the module’s default values using functiontcc_get_config_defaults :
struct tcc_config config_tcc;
static void configure_tcc(void)
{
struct tcc_config config_tcc;
tcc_get_config_defaults(&config_tcc, TCC0);
}
TCC0 definition corresponds to the TCC0 peripheral base address.
The TCC0 peripheral has four different compare/capture channels. Each channel has a dedicated register
(CC0 to CC3).
TCC0 has also an output matrix can distribute and route out the TCC waveform outputs across the port which
pins in different configurations, each optimized for different application types.
By default, the Output Matrix Channel Pin Routing Configuration is the following:
Compare and Capture registers Waveform Output pins
CC0 WO[0], WO[4]
CC1 WO[1], WO[5]
CC2 WO[2], WO[6]
CC3 WO[3], WO[7]
As a consequence, the Channel 2 Compare and Capture register (CC2) must be
used to output the PWM signal on WO[6].
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• Update default TCC settings to configure:
• T P -he eriod register to get a resolution(PER) value of 16 bit for the PWM waveform
• The formwave generation mode Slope PWMto Single-
• The ompare and to the Channel 2 C Capture register (CC2) value half period register
value to get a duty cycle of 50%
struct tcc_config config_tcc;
static void configure_tcc(void)
{
struct tcc_config config_tcc;
tcc_get_config_defaults(&config_tcc, CONF_PWM_MODULE);
config_tcc.counter.period = 0xFFFF;
config_tcc.compare.wave_generation =
TCC_WAVE_GENERATION_SINGLE_SLOPE_PWM;
2 ; config_tcc.compare.match[ ] = 0x7FFF
}
The following equation calculates the exact resolution for a single-slope PWM
waveform:
𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 =log ( + 1)𝑃𝐸𝑅
log (2)
To get a 16 bit resolution, PER must be - equal to 65535 . 0xFFFF
• Update default TCC settings to:
• Enable the PWM waveform output pin WO[6]
• Specify the WO[6] pin output which is PIN_PB12F_TCC0_WO6
• Specify the WO[6] peripheral multiplexing port MUX_PB12F_TCC0_WO6which is
config_tcc.pins.enable_wave_out_pin[6 ] = true;
config_tcc.pins.wave_out_pin[ PIN_PB12F_TCC0_WO66] = ;
config_tcc.pins.wave_out_pin_mux[ MUX_PB12F_TCC0_WO66] = ;
• Configure the TCC module with the desired settings:
tcc_init(&tcc_instance, TCC0, &config_tcc);
• Enable the TCC module to start the timer and begin PWM signal generation:
tcc_enable(&tcc_instance);
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TCC0 initialization is completed.
struct tcc_module tcc_instance;
static void configure_tcc(void)
{
struct tcc_config config_tcc;
tcc_get_config_defaults(&config_tcc, TCC0);
config_tcc.counter.period = 0xFFFF;
config_tcc.compare.wave_generation =
TCC_WAVE_GENERATION_SINGLE_SLOPE_PWM;
config_tcc.compare.match[2] = 0x7FFF;
config_tcc.pins.enable_wave_out_pin[6] = true;
config_tcc.pins.wave_out_pin[6] = PIN_PB12F_TCC0_WO6;
config_tcc.pins.wave_out_pin_mux[6] = MUX_PB12F_TCC0_WO6;
tcc_init(&tcc_instance, TCC0, &config_tcc);
tcc_enable(&tcc_instance);
}
AN- – -9232 Single slope PWM Implementation using SAM D21 TCC in a Touch-based Application: 42327 2014A 07/−
Page 34 44 of
Test PWM S Iignal mplementation.
• Call the configure_tcc function in your main function:
int main (void)
{
s ystem_init();
configure_tcc();
In STANDBY sleep mode, all clocks and functions are stopped expect those selected
to continue running.
• Disable the entry in sleep mode by commenting so that STANDBY system_sleep function the
TCC0 clock and so the waveform output WO[6] are not disabled
while (1) {
/**
* Goto STANDBY sleep mode, unless woken by timer or PTC
interrupt.
*/
//system_sleep();
• Build the solution and ensure you get no errors:
• Program the application by clicking on the Start Without Debugging icon:
• Press RESET button on the SAM D21 Xplained Pro
You can see the LED8 lit.
5.3 Conclusion
In this assignment, you have learnt:
• How to configure the TCC to generate a PWM signal
• How to configure the TCC to output a PWM signal on a Waveform Output pin WO[x]dedicated
AN- – -9232 Single slope PWM Implementation using SAM D21 TCC in a Touch-based Application: 42327 2014A 07/−
Page 35 44 of
6. Use Assignment 4: QTouch Button to Control LED Brightness
In this assignment, the PWM duty cycle of waveform output will be configured to control the WO[6] signal
LED8 brightness in relation to the BUTTON 1 Touch Delta value .
Here are the steps to complete this assignment:to follow in order
• Use QTouch Library API to read BUTTON 1 Touch Delta value
• Update Waveform Output WO[6] duty cycle Touch Delta valuein relation to BUTTON 1
6.1 Reading and using Button Touch Delta Value
We will use the API function called to retrieve the delta value touch_selfcap_sensor_get_delta
corresponding to BUTTON 1.
Here is the API function definition for Self Capacitance technol ogy:
touch_ret_t touch_selfcap_sensor_get_delta(
sensor_id_t sensor_id,
touch_delta_t *p_delta);
Where:
• sensor_id is the sensor ID for which delta value is being retrieved
• p_delta is the pointer to the delta variable to be updated by the Touch Library
This API function is defined in touch_api_SAMD.h from QTouch folder.
The ON/OFF state of a button as the slider/rotor position, are touch status parameters.
These parameters must be read by the application only after the measurement_done_touch flag set.is
This . flag is part of the measure data structuretouch called touch_measure_data_t
A pointer to this data structure is already declared in and initialized by the touch.c
QTouch library:
/* ! Self capacitance method measured data pointer. */
touch_measure_data_t *p_selfcap_measure_data = NULL;
So, the following code can be used to quickly implement a read of the Touch Delta value of a sensorspecific :
/* ! Start Touch Sensor Measurement. */
touch_sensors_measure();
/* Update touch status once measurement complete flag is set. */
if ((p_ >measurement_done_touch == 1u))selfcap_measure_data-
{
p_selfcap_measure_data->measurement_done_touch = 0;
touch_selfcap_sensor_get_delta(sensor_id, p_delta);
}
AN- – -9232 Single slope PWM Implementation using SAM D21 TCC in a Touch-based Application: 42327 2014A 07/−
Page 40 44 of
The application needs to have LED8 switched off when there is no touch or proximity touch.
On the QT1 Xplained extension board turned off when PIN_PB12 is set:, LED8 is
So, the solution tis o invert the PWM the wavefwaveform output signal thanks to orm output polarity feature of
the SAM D21 TCC : (POLx bit)
POLx Waveform Generation Output Update
Set Clear
0 Timer/counter matches
TOP
Timer/counter matches CCx
1 Timer/counter matches CCx Timer/counter matches TOP
POLx = 0 by default where x is th TCC Channel Ne umber.
If = POLx ‘1’, waveform output pin becomes:
• Cleared at start or on compare match between the counter (COUNT) and
period (PER) registers’ values (TOP)
• Set on compare match between the counter (COUNT) and Compare/Capture
(CCx) registers’ values

Product specificaties

Merk: Microchip
Categorie: Niet gecategoriseerd
Model: ATSAMD21E16

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