CE54365 - CSD with I2CHW Slave on CY8C21x34/B.pdf

CE54365 – CSD with I2CHW Slave on
CY8C21x34/B
Objective
This code example demonstrates how to use CapSense Sigma Delta (CSD) User Module (UM) in CY8C21x34/B device to
scan CapSense button sensors and send the sensor data to the master using I2C protocol.
Overview
This code example shows how to implement CapSense button sensors with the CY8C21x34/B device using the CSD UM in
the PSoC Designer™ Integrated Design Environment (IDE). It also shows how to send the sensor data to the I2C master using
the I2CHW UM.
This code example can be tested with the CY3280-21x34 Universal CapSense Controller (UCC) board.
PSoC Resources
Cypress provides a wealth of data at www.cypress.com to help you to select the right PSoC® device for your design and
quickly and effectively integrate the device into your design. For a comprehensive list of resources, see KBA92181 –
Resources Available for CapSense Controllers. The following is an abbreviated list for CapSense devices:
 Overview: CapSense Portfolio, CapSense Roadmap.
 Development Kits:
 Product Selectors: CapSense, CapSense Plus™,
CapSense Express™, PSoC 3 with CapSense,
PSoC 5 with CapSense, PSoC 4. In addition,
PSoC Designer offers a device selection tool when you
create a new project.
 Datasheets:
Describe
and
provide
electrical
specifications for the CapSense, PSoC 1, PSoC 3,
PSoC 4, and PSoC 5LP device families.
 Application Notes: Cypress offers CapSense
application notes covering a broad range of topics,
from basic to advanced level. Recommended
application notes for getting started with CapSense are
the following:



AN64846 – Getting Started With CapSense
CY8C21x34/B – CapSense Design Guide
AN2397 – PSoC 1 and CapSense Controllers –
CapSense Data Monitoring Tools
 Technical Reference Manuals (TRM): Provide
detailed descriptions of the architecture and registers
in the CapSense, PSoC 1, PSoC 3, PSoC 4, and
PSoC 5LP device families.

CY3280-BK1 – Universal CapSense Controller –
Basic Kit 1 features a predefined control circuitry
and plug-in hardware to make prototyping and
debugging easy. The kit includes MiniProg1
programming hardware for device programming
and CY3240-I2USB board hardware for tuning and
data acquisition.

CY3280 – SLM Linear Slider Module Kit consists
of 5 CapSense buttons, 1 linear slider (with 10
sensors), and 5 LEDs. This module connects to
the CY3280 UCC board, including the CY328021x34 UCC board.

CY3280-BBM – Matrix Button Module Kit consists
of 8 LEDs as well as 8 CapSense sensors
organized in a 4x4 matrix format to form 16
physical buttons.
 Programming Resources:

PSoC supports a number of different programming
modes and tools. For more information, see the
General Programming page.
PSoC Designer
PSoC Designer is a free, Windows-based IDE. It enables the hardware and firmware to be designed concurrently for systems
based on PSoC 1 and CapSense devices; see Figure 1. With PSoC Designer, you can:

Drag and drop UMs to build your hardware system
design in the main design workspace

Codesign your application firmware with the PSoC
hardware
www.cypress.com



Configure UMs
Explore the library of UMs
Review UM datasheets
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CSD with I2CHW Slave on CY8C21x34/B
Figure 1. PSoC Designer Features
Requirements
Tool: PSoC Designer 5.4 SP1, Bridge Control Panel (BCP)
Programming Language: C (ImageCraft STD and PRO compilers)
Associated Parts: CY8C21x34/B device series
Related Hardware: CY3280-BK1 – Universal CapSense Controller – Basic Kit 1
Design
Figure 2 shows the schematic design of the code example. The code example features the following:

CSD UM to detect a finger touch on the CapSense button sensor



The CSD UM is configured to scan five CapSense button sensors.
All CSD parameters are manually set to achieve optimum touch sensing performance.
I2CHW UM to send the CapSense button sensor data to the I2C master

The sensor data (Raw Count, Baseline, Difference Count, and Status) of the specified button sensor is stored in the
I2C read buffer.
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CSD with I2CHW Slave on CY8C21x34/B
Figure 2. CSD Design with CY8C21434
Design Considerations
In the code example, the resolution parameter is set to ‘12’, assuming the overlay thickness on the sensor board is 1.5 mm. To
test the code example with an overlay of a different thickness, set the resolution parameter so that the ratio of difference count
to noise count is greater than 5:1. Thicker overlays require you to scan at a higher resolution to achieve an SNR greater than
5:1. Refer to the flow chart in Figure 3 to tune the CSD parameters to achieve an SNR > 5:1. For the detailed tuning
procedure, refer to the CY8C21x34/B – CapSense Design Guide.
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CSD with I2CHW Slave on CY8C21x34/B
Figure 3. CSD Tuning Flow Chart
Start
Apply Default Settings
Sysclk = 24MHz
SensorAutoreset = Disabled
PRS = PRS16
Scanning Speed = Normal
Resolution(N) = 12bit
RefValue(REF) = 4
Cmod = 10nF
Rb = 2.2kΩ
Gather Raw Counts using
CY3240-I2USB Bridge
Or
UART(TX8) (Refer AN2397)
Make sure this is done with
no finger on the sensor
Choose the sensor with the
highest raw counts to
proceed with tuning
Choose PRS8 with Prescaler and set
Period so that
?
N
Where Rs ≈ 560Ω
Y
Set New Rb to obtain 70% of total counts
Set New Rb to obtain 70% of total counts
Replace Rb on the board with New Rb
Replace Rb on the board with New Rb
Measure SNR where:
Signal = fingeron-fingeroff
Noise = finger off pk-pk
SNR = Signal/Noise
refer to AN66271
Calculate Cp
SNR ≥ 5 ?
N
Increase
Resolution(N)
or
Decrease Scan Speed
Period = 1 (No Prescaler)
Y
Calculate F
F = Sysclk/4
Calculate RefValue for each sensor so it is as close
as possible to 70% of total counts
Calculate Cp for each
sensor
Where Period = 1 if no prescaler is being used.
Total Scan Time for All
sensors meets System
Requirments?
N
Decrease
Resolution(N)
or
Increase Scan Speed
For Sensors SNR>9
Y
1
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CSD with I2CHW Slave on CY8C21x34/B
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Using Difference Counts
Calculate the following values. If
there is a large discrepancy in
difference counts between
sensors set separate thresholds
for each sensor
Set Finger Threshold to 75% of
Peak when finger present
Set Hysteresis to 15% of Peak
when finger present
Set Noise Threshold to 40% of
Peak
When finger present
Set Negative Noise Threshold
equal to Noise Threshold
Run Environmental testing to set
Baseline Update Threshold
Set AutoReset and Debounce
based on customer spec
End
Hardware Setup
For the basic kit board setup, see the corresponding kit user guide.
The code example can be tested on CY3280-21x34 UCC board with the CY3280-SLM board. Follow these steps to set up the
hardware:
1.
Connect the CY3280-SLM board to the P2 receptacle connector of the CY3280-21x34 UCC board, as shown in Figure 4.
2.
On the CY3280-21x34 UCC board, place a jumper on header J1 to short pins 2 and 3. This setting allows the CapSense
controller to be powered from ISSP connector J3.
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CSD with I2CHW Slave on CY8C21x34/B
3.
On the CY3280-21x34 UCC board, place a jumper on header J4 to short pins 1 and 2. This setting routes the XRES pin of
the CapSense controller to pin 3 of ISSP connector J3.
4.
On the CY3280-SLM board, place a jumper on header J2 to short pins 2 and 3. This setting connects the shield traces on
the CY3280-SLM board to ground.
5.
Connect your PC to the CY3280-21x34 UCC board's ISSP connector J3 using MiniProg1 or MiniProg3 and a USB cable.
Figure 4. Hardware Setup for Testing Code Example
Software Setup
The code example works on CY3280-21x34 UCC board with the CY3280-SLM board without any modification. To test the
code example on a custom board, reassign the sensor pins and retune the CSD parameters according to the flow chart in
Figure 3. To reassign the sensor pins, refer to the “CSD Wizard” section in the CapSense Sigma-Delta UM datasheet.
User Modules
Table 1 lists the PSoC Designer UMs used in the code example, as well as the hardware resources used by each.
Table 1. PSoC Designer User Modules
User Modules
Hardware Resources
CSD
ACE00, ACE01, ASE11, DBB00, DBB01, DCB02
I2CHW
No blocks occupied (uses dedicated hardware)
Parameter Settings
Table 2 to Table 4 show the parameter settings for the UMs used in the code example. Only the parameters that vary from the
default are shown.
Table 2. CSD User Module Settings
Parameter
Value
Comments
Finger Threshold
75
After the difference count crosses the finger threshold plus hysteresis, the button is
said to be in “ON” condition.
Noise Threshold
40
If the difference count is less than the noise threshold, it is treated as noise, and the
baseline update algorithm handles it by putting it into the update bucket.
100
As the noise increases, the update bucket is filled, and every time it crosses this
threshold, the baseline is incremented by ‘1’ and the algorithm continues.
Baseline
Update Threshold
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CSD with I2CHW Slave on CY8C21x34/B
Parameter
Value
Comments
Sensors Autoreset
Disabled
When the parameter is set to “disabled,” the baseline is updated only when the raw
count and baseline difference is below the noise threshold parameter.
Hysteresis
15
This parameter handles false ON and OFF situations whenever the button is pressed.
Set it equal to the noise threshold.
Debounce
3
If the difference count is more than the finger threshold for less than the “debounce”
number of samples, it is not taken as a button press.
Negative Noise Threshold
40
If the raw count is below the baseline and the difference count is more than this
threshold, the baseline is not updated.
Low Baseline Reset
50
If the raw count is below the baseline and the difference count is more than the
negative noise threshold for the number of samples given by this parameter, the
baseline is reset to a new raw count.
Scanning Speed
Normal
This parameter decides the speed of the scanning process.
Resolution
12
The higher the resolution, the higher is the sensitivity.
Modulator Capacitor Pin
P0[3]
This parameter indicates to which pin Cmod is connected.
Feedback Resistor Pin
P3[1]
This parameter indicates to which pin Rb is connected.
Reference
ASE11
This parameter indicates the source for reference voltage. ASE11 is preferred.
Ref Value
2
This parameter sets the comparator reference value.
Prescaler Period
3
This parameter sets the prescaler period register and determines the precharge switch
output frequency.
ShieldElectrodeOut
None
The shield electrode is not used in this code example.
Table 3. I2CHW User Module Settings
Parameter
Value
Comments
Slave Address
4
This parameter decides the address that is assigned to the slave. The value assigned
can be any value from 0 to 127 (decimal).
Read_Buffer_Types
RAM ONLY
Only the RAM data buffer is used.
Communication_Service_Type
Interrupt
See the following notes.
I2C Clock
100k Standard
This parameter decides the maximum clock speed at which the slave can operate.
I2C Pin
P1[0]–P1[1]
This parameter specifies which pins are used as the SDA and SCL lines of I2C.
Notes:

When the Read_Buffer_Types is set to RAM ONLY, only RAM buffers may be transmitted over I 2C. If data from the flash
buffer is to be read and transmitted, the read buffer type should be set to RAM OR FLASH.

In an interrupt-based Communication_Service_Type, data is moved in and out of the buffer very quickly in the background
using an ISR.

The I2C clock is dependent on the SysClk. The I2C clock setting in the UM is based on a SysClk of 24 MHz. In devices
that support slower a Sysclk, the I2C clock is reduced by the same proportion. For example, if the I2C clock is set to
400 kHz and SysClk is set to 6 MHz, the actual I2C clock is only 100 kHz.
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CSD with I2CHW Slave on CY8C21x34/B
Table 4. Global Resources Settings
Parameter
Value
Comments
Power Setting (Vcc/SysClk
frequency)
5.0 V/24 MHz
Selects 5-V operation and 24-MHz SysClk.
CPU_Clock
SysClk/2
Selects 12 MHz as CPU clock.
Note: Other parameters are left at their default values.
Operation
Build and install the example in the CY3280-21x34 UCC board . Refer to the kit user guide for the procedure to build and
install the example project.
On reset, all the hardware settings from the device configuration are loaded into the device and main.c is executed. The
following operations are performed by the firmware:

A structure (sI2CRegs) is defined to store the button number, raw count, difference count, baseline, and status of the
CapSense button.

A global interrupt is enabled and the CSD UM is started, finger thresholds for the buttons are set, and baselines are
initialized.

The I2CHW UM is started. Structure “sI2CRegs” is set as the I2C read buffer, and the BYTE variable “buttonNumber” is set
as the I2C write buffer.

To get information about a button, the I2C master must write the button number into the I2C write buffer (buttonNumber).
The I2C master can get that button information by reading the I2C read buffer (sI2CRegs).

In an infinite while loop, all the CapSense buttons are scanned, and all the baselines are updated. Also, sI2CRegs is
updated with the raw count, difference count, baseline, and status of the requested CapSense button.

Whenever the I2C master writes (or reads) into the buffer, the Write flag (Read flag) must be reset and the buffer must be
set again. This operation is done in the while loop.
Test the example by doing the following:
1.
Open the BCP software from Start > All Programs > Cypress > Bridge Control Panel [version] > Bridge Control
Panel [version].
2.
Connect the CY3240 USB-I2C Bridge to header J3 on the CY3280-21x34 UCC board. Refer to the CY3240-I2USB USBI2C Bridge Guide for information on how to connect the CY3240 USB-I2C Bridge to any kit for I2C communication.
If you are using MiniProg3, see the MiniProg3 User Guide for information on how to connect the I2C pins of the CapSense
controller to MiniProg3.
3.
In the BCP software, ensure that the USB-I2C Bridge or MiniProg3 is listed in the Connected I2C/SPI/RX8 Ports: tab, as
shown in Figure 5.
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CSD with I2CHW Slave on CY8C21x34/B
Figure 5. Selecting the USB-I2C Bridge or MiniProg3 in BCP
4.
Choose Tools > Protocol Configuration, select I2C Speed – 100 kHz, and click OK.
5.
At the right bottom corner under Power, select the +5.0V radio button. This powers the target device with 5 V
6.
At the left bottom corner, click the List button. This lists all the slave device addresses. In this case, the device address 04
is the slave address of the CapSense controller, and it is displayed in the status window, as shown in Figure 6.
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CSD with I2CHW Slave on CY8C21x34/B
Figure 6. Display of Slave Address in Status Window
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CSD with I2CHW Slave on CY8C21x34/B
7.
To monitor the CapSense data of button 0, write the following command in the command window (Figure 7) and press
Enter.
W 04 00
Figure 7. Write Command Execution
Button# 0
Slave Address
Write Command
Plus Indicates Positive
Acknowledgment from Slave
8.
To view CapSense data as a graph, click the Chart tab and select Variable Settings.
9.
In the Variable Settings window, select the Variables tab, as shown in Figure 8. In the Active column, select the first
four check boxes.
10. In the Variable Name column, enter the first four names as RC (raw count), DC (difference count), BL (baseline), and
Status (button ON/OFF status).
11. In the Type column, select int for RC, DC, and BL. Select byte for Status and click OK.
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CSD with I2CHW Slave on CY8C21x34/B
Figure 8. Variable Settings Window
12. In the BCP Editor window, press [Ctrl] [Enter] in the line “W 04 00” to move the cursor to the next line.
13. Write the following command in the command window, as shown in Figure 9:
R 04 @1RC @0RC @1DC @0DC @1BL @0BL @Status [DELAY=15]
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CSD with I2CHW Slave on CY8C21x34/B
Figure 9. Read Command Execution
LSB of Variable RC
MSB of Variable RC
Slave Address
Read Command
Note: The [DELAY=15] command provides a delay of 15 ms before the next I 2C transaction occurs when the Repeat button is
clicked. This delay provides sufficient time for the I2C buffer to reinitialize the read pointer to the beginning of the buffer after
the previous read is completed. If a delay is not inserted, then the I2C master will read the values as zeros until the pointer is
reinitialized.
14. Click the Chart tab and then click the Repeat button. Now you can see the CapSense data.
15. To monitor only raw counts, deselect DC, BL, and Status, as shown in Figure 10. The raw counts when the CapSense
button sensor is touched is show in Figure 11.
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CSD with I2CHW Slave on CY8C21x34/B
Figure 10. Raw Counts Chart When CapSense Button Sensor is Not Touched
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CSD with I2CHW Slave on CY8C21x34/B
Figure 11. Raw Counts Chart when CapSense Button Sensor is Touched
Related Documents
Table 5 lists the relevant application notes, design guides, code examples, UM datasheets, and device and development kit
documentation.
Table 5. Related Documents
Application Notes
AN75320
Getting Started with PSoC 1
Learn about the PSoC 1 architecture and the development tools required
to design an embedded system with the PSoC 1 device family.
AN50987
Getting Started with I2C in
PSoC 1
Learn how I2C communication works and how to implement I2C
communication in PSoC 1.
AN2397
PSoC 1 and CapSense
Controllers – CapSense Data
Monitoring Tools
Learn how to use I2C communication to tune and debug a CapSense
system.
Design Guides
www.cypress.com
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CSD with I2CHW Slave on CY8C21x34/B
AN64846 – Getting Started with CapSense
This guide is an ideal starting point if you are new to capacitive touch
sensing (CapSense). It is also useful for learning key design
considerations and layout best practices to ensure design success.
CY8C21x34/B – CapSense Design Guide
This document provides design guidance for building CapSense
applications with the CY8C21x34 family of devices.
Code Examples
CapSense Controller Code Examples
This document shows how to measure sensor parasitic capacitance from
a CapSense controller, read CapSense sensor data, and tune the
CapSense parameters.
PSoC Designer User Module Datasheets
CSD
The CSD UM controls the CapSense CSD block and detects changes in
capacitance in applications such as touch sense buttons, sliders,
touchpad, and proximity detection.
I2CHW
The I2C Hardware UM implements an I2C device in firmware. The I2CHW
UM supports the standard mode with speeds up to 400 kbps.
Device Documentation
CY8C21x34/B Datasheet
CY8C21x34/B Technical Reference Manual
Development Kit Documentation
CY3280-BK1  Universal CapSense Controller Basic Kit 1 User Guide
www.cypress.com
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CSD with I2CHW Slave on CY8C21x34/B
Document History
Document Title: CE54365 - CSD with I2CHW Slave on CY8C21x34/B
Document Number: 001-54365
Revision
ECN
Orig. of
Change
Submission
Date
Description of Change
**
2727566
ARVM
07/14/2009
New example project
*A
2973490
ARVM
07/20/2010
Updated the software version to "PD5.0 SP6 Build 1127". Added "Related
Hardware" and "Author" fields on page 1, below the title.
*B
3124139
ARVM
12/30/2010
Updated the project to use 3280-21x34 UCC and SLM boards.
*C
3319209
UDYG/ARVM
07/19/2011
Updated the software version to “PD5.1 SP2 Build 2306”.
Renamed Example projects to Code Examples in the title and document.
*D
3689951
SSHH
07/23/2012
No change. Completing sunset review.
*E
4871331
DCHE
08/04/2015
Update code example to latest template.
Updated all figures in the document to match latest tool snapshot.
Updated project to PSoC Designer 5.4 SP1.
www.cypress.com
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CSD with I2CHW Slave on CY8C21x34/B
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© Cypress Semiconductor Corporation, 2009-2015. The information contained herein is subject to change without notice. Cypress Semiconductor
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use of any product or circuit described herein. Cypress does not authorize its products for use as critical components in life-support systems where a
malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress’ product in a life-support systems
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Document No. 001-54365 Rev.*E
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