CPT112S Data Sheet

TouchXpress™ Family
CPT112S Data Sheet
The CPT112S device, part of the TouchXpress family, is designed
to quickly add capacitive touch via an I2C interface by eliminating
the firmware complexity and reducing the development time for capacitive sensing applications.
Supporting up to 12 capacitive sensor inputs in a 3 mm x 3 mm QFN package, the
CPT112S is a highly-integrated device that interfaces via I2C to the host processor to
provide a simple solution for adding capacitive touch. The device also comes with advanced features like moisture immunity, wake-on proximity, and buzzer feedback for an
enhanced user experience. No firmware development is needed, and all the capacitive
touch sense parameters can be configured using a simple GUI-based configurator. By
eliminating the need for complex firmware development, the CPT112S device enables
rapid user interface designs with minimal development effort.
The CPT112S device is ideal for a wide range of capacitive touch applications including
the following:
• Medical equipment
• Consumer electronics
• Lighting control
• Home appliances
• Instrument / Control panels
• White goods
Input
Features
Capacitive Touch Sensing
Features
KEY FEATURES
• No firmware development required
• Simple GUI-based configurator
• 12 Capacitive Sensor inputs with
programmable sensitivity
• Configurable multi-button slider
• I2C interface to communicate to the host
• Lowest power capacitive sense solution
• Active — 200 µA
• Sleep — 1 µA
• Wake on proximity
• Superior noise immunity: SNR up to 270:1
• Moisture immunity
• Mutually-exclusive touch qualifier
• Button touch time-out to avoid false
touches
• Buzzer output for audible touch feedback
Output
Features
Proximity Wake
Input
Touch
Qualification
MutuallyExclusive Touch
Qualifier
I2C Output
I2C Event Buffer
Option for a
Multi-Button
Slider
Configuration
Profile for each
Input
Baselining
Interrupt Pin
Optional Buzzer
Output
Input Engine
with
12 Inputs
Low Power State
Machine
Touch Time-Out
Timer
Lowest power mode with feature operational:
Active
Optimized Active
Low Power Sleep
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This information applies to a product under development. Its characteristics and specifications are subject to change without notice.
Preliminary Rev. 0.1
CPT112S Data Sheet
Feature List and Ordering Information
1. Feature List and Ordering Information
The CPT112S has the following features:
• Capacitive sensing input engine with 12 inputs
• Post-sample touch qualification engine
• Configuration profile space in non-volatile memory
• I2C event buffer with interrupt pin to signal when new touch events have been qualified
• Low power state machine to minimize current draw in all use cases
• Capacitive proximity sensing input
• Buzzer output
• Mutually-exclusive touch qualifier
• Touch time-out timer
CP T 1 12 S – A 01 – G M R
Tape and Reel (Optional)
Package Type
Temperature Grade — –40 to +85 °C (G)
Firmware Revision
Hardware Revision
Capacitive Sense Features — Slider (S)
Number of Capacitive Sense Inputs
Interface Type — GPO (0), I2C (1)
TouchXpress Family
Silicon Labs Xpress Product Line
Figure 1.1. CPT112S Part Numbering
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Preliminary Rev. 0.1 | 1
CPT112S Data Sheet
Typical Connection Diagrams
2. Typical Connection Diagrams
2.1 Signal, Analog, and Power connections
Figure 2.1 Connection Diagram on page 2 shows a typical connection diagram for the power pins of CPT112S devices.
CPT112S
Device
1.8-3.6 V (in)
4.7 µF and 0.1 µF
bypass capacitors
required for the power
pins placed as close to
the pins as possible.
VDD
GND
1.8-3.6 V (in)
Host
Processor
EB_SCL
EB_SDA
EB_INT
CS00
Electrode
...
CS10
Electrode
1.8-3.6 V (in)
Config Data
Config Clk / RSTb
Figure 2.1. Connection Diagram
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CPT112S Data Sheet
Typical Connection Diagrams
2.2 Configuration
The diagram below shows a typical connection diagram for the configuration connections pins. The ToolStick Base Adapter is available
on the evaluation board.
CPT112S Device
VDD
1k
Config Clk
Config Data
GND
ToolStick
Figure 2.2. Configuration Connection Diagram
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Preliminary Rev. 0.1 | 3
CPT112S Data Sheet
Electrical Specifications
3. Electrical Specifications
3.1 Electrical Characteristics
All electrical parameters in all tables are specified under the conditions listed in Table 3.1 Recommended Operating Conditions on page
4, unless stated otherwise.
3.1.1 Recommended Operating Conditions
Table 3.1. Recommended Operating Conditions
Parameter
Symbol
Operating Supply Voltage on VDD
VDD
Minimum RAM Data Retention
Voltage on VDD1
VRAM
Operating Ambient Temperature
TA
Test Condition
Min
Typ
Max
Unit
1.8
2.4
3.6
V
Not in Sleep Mode
—
1.4
—
V
Sleep Mode
—
0.3
0.5
V
–40
—
85
°C
Note:
1. All voltages with respect to GND.
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CPT112S Data Sheet
Electrical Specifications
3.1.2 Power Consumption
See 3.4 Typical Performance Curves for power consumption plots.
Table 3.2. Power Consumption
Parameter
Symbol
Active Mode Supply Current
Min
Typ
Max
Unit
IDD
—
3.1
—
mA
Optimized Active Mode Supply
Current
IDD
—
180
—
µA
Sleep Mode Current1, 2
IDD
3 sensors or fewer
—
0.78
—
µA
4 sensors
—
0.79
—
µA
5 sensors
—
0.81
—
µA
6 sensors
—
0.82
—
µA
7 sensors
—
0.84
—
µA
10 sensors
—
0.88
—
µA
12 sensors
—
0.95
—
µA
Scan period = 10 ms
—
154
—
µA
Scan period = 20 ms
—
77
—
µA
Scan period = 50 ms
—
31
—
µA
Scan period = 75 ms
—
21
—
µA
Scan period = 100 ms
—
16
—
µA
Scan period = 10 ms
—
47
—
µA
Scan period = 20 ms
—
23
—
µA
Scan period = 50 ms
—
9
—
µA
Scan period = 75 ms
—
6
—
µA
Scan period = 100 ms
—
5
—
µA
System Current with Varying Scan
Time — Base with One Sensor1
System Current with Varying Scan
Time — Each Additional Sensor1
IDD
IDD
Test Condition
Note:
1. Measured with Free Run Mode disabled and sensors set to 4x accumulation, 8x gain.
2. Measured with scan period set to 250 ms.
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CPT112S Data Sheet
Electrical Specifications
3.1.3 Reset and Supply Monitor
Table 3.3. Reset and Supply Monitor
Parameter
Symbol
Test Condition
Min
Typ
Max
Unit
VDD Supply Monitor Threshold
VVDDM
Reset Trigger
1.7
1.75
1.8
V
VWARN
Early Warning
1.8
1.85
1.9
V
Power-On Reset (POR) Monitor
Threshold
VPOR
Rising Voltage on VDD
—
1.75
—
V
Falling Voltage on VDD
0.75
1.0
1.3
V
VDD Ramp Time
tRMP
—
—
3
ms
RST Low Time to Generate Reset
tRSTL
15
—
—
µs
Boot Time1
tboot
1 sensor
—
25
—
ms
2 sensors
—
40
—
ms
3 sensors
—
55
—
ms
4 sensors
—
70
—
ms
5 sensors
—
85
—
ms
6 sensors
—
100
—
ms
7 sensors
—
115
—
ms
8 sensors
—
130
—
ms
9 sensors
—
145
—
ms
10 sensors
—
160
—
ms
11 sensors
—
175
—
ms
12 sensors
—
200
—
ms
Time to VDD ≥ 1.8 V
Note:
1. Boot time is defined as the time from a power-on reset or /RST pin release until the first capacitive sense scan begins.
3.1.4 Configuration Memory
Table 3.4. Configuration Memory
Parameter
Symbol
Endurance (Write/Erase Cycles)
NWE
Test Condition
Min
Typ
Max
Units
20 k
100 k
—
Cycles
Note:
1. Data Retention Information is published in the Quarterly Quality and Reliability Report.
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CPT112S Data Sheet
Electrical Specifications
3.1.5 Capacitive Sense
Table 3.5. Capacitive Sense
Parameter
Symbol
Test Condition
Scan Time Per Sensor1
tSCAN
Signal to Noise Ratio1, 2
Conversion Time
Total Processing Time3
Maximum External Capacitive
Load
SNR
tCONV
tPROC
CEXTMAX
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Min
Typ
Max
Unit
Accumulation = 1x
—
64
—
µs
Accumulation = 4x
—
256
—
µs
Accumulation = 8x
—
512
—
µs
Accumulation = 16x
—
1.024
—
ms
Accumulation = 32x
—
2.048
—
ms
Accumulation = 64x
—
4.096
—
ms
Accumulation = 1x
—
90:1
—
codes
Accumulation = 4x
—
180:1
—
codes
Accumulation = 8x
—
182:1
—
codes
Accumulation = 16x
—
210:1
—
codes
Accumulation = 32x
—
230:1
—
codes
Accumulation = 64x
—
270:1
—
codes
Gain = 1x
—
205
—
µs
Gain = 2x
—
123
—
µs
Gain = 3x
—
98
—
µs
Gain = 4x
—
85
—
µs
Gain = 5x
—
76
—
µs
Gain = 6x
—
72
—
µs
Gain = 7x
—
67
—
µs
Gain = 8x
—
64
—
µs
1 sensor
—
576
—
µs
2 sensors
—
796
—
µs
3 sensors
—
1.0
—
ms
4 sensors
—
1.2
—
ms
5 sensors
—
1.4
—
ms
6 sensors
—
1.7
—
ms
7 sensors
—
1.9
—
ms
8 sensors
—
2.1
—
ms
9 sensors
—
2.3
—
ms
10 sensors
—
2.6
—
ms
11 sensors
—
2.8
—
ms
12 sensors
—
3.0
—
ms
Gain = 8x
—
45
—
pF
Gain = 1x
—
500
—
pF
Preliminary Rev. 0.1 | 7
CPT112S Data Sheet
Electrical Specifications
Parameter
Symbol
Test Condition
Maximum External Series Impedance
REXTMAX
Gain = 8x
Min
Typ
Max
Unit
—
50
—
kΩ
Note:
1. Measured with gain set to 8x.
2. Measured with an evaluation board with 1/16" overlay using Capacitive Sense Profiler.
3. Sensors configured to 8x gain, 1x accumulation with sensor sampling and system processing time included and mutually-exclusive buttons, slider, buzzer, and touch time-outs disabled.
3.1.6 Buzzer Output
Table 3.6. Buzzer Output
Parameter
Symbol
Test Condition
Min
Typ
Max
Unit
Output High Voltage (High Drive)
VOH
IOH = –3 mA
VDD – 0.7
—
—
V
Output Low Voltage (High Drive)
VOL
IOL = 8.5 mA
—
—
0.6
V
Output High Voltage (Low Drive)
VOH
IOH = –1 mA
VDD – 0.7
—
—
V
Output Low Voltage (Low Drive)
VOL
IOL = 1.4 mA
—
—
0.6
V
Weak Pull-Up Current
IPU
VDD = 1.8 V
—
–4
—
µA
–35
–20
—
µA
Min
Typ
Max
Unit
—
60
—
°C/W
VIN = 0 V
VDD = 3.6 V
VIN = 0 V
3.2 Thermal Conditions
Table 3.7. Thermal Conditions
Parameter
Symbol
Thermal Resistance*
θJA
Test Condition
Note:
1. Thermal resistance assumes a multi-layer PCB with any exposed pad soldered to a PCB pad.
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CPT112S Data Sheet
Electrical Specifications
3.3 Absolute Maximum Ratings
Stresses above those listed in Table 3.8 Absolute Maximum Ratings on page 9 may cause permanent damage to the device. This is
a stress rating only and functional operation of the devices at those or any other conditions above those indicated in the operation listings of this specification is not implied. Exposure to maximum rating conditions for extended periods may affect device reliability. For
more information on the available quality and reliability data, see the Quality and Reliability Monitor Report at http://www.silabs.com/
support/quality/pages/default.aspx.
Table 3.8. Absolute Maximum Ratings
Parameter
Symbol
Ambient Temperature Under Bias
Test Condition
Min
Max
Unit
TBIAS
–55
125
°C
Storage Temperature
TSTG
–65
150
°C
Voltage on VDD
VDD
GND–0.3
4.0
V
Voltage on I/O pins or RSTb
VIN
GND–0.3
VDD + 0.3
V
Total Current Sunk into Supply Pin
IVDD
—
400
mA
Total Current Sourced out of Ground
Pin
IGND
400
—
mA
Current Sourced or Sunk by Any I/O
Pin or RSTb
IIO
–100
100
mA
Maximum Total Current through all
Port Pins
IIOTOT
—
200
mA
Operating Junction Temperature
TJ
–40
105
°C
Exposure to maximum rating conditions for extended periods may affect device reliability.
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CPT112S Data Sheet
Electrical Specifications
3.4 Typical Performance Curves
Figure 3.1. Active Mode Processing Time Per Sensor
Note: Active mode processing time per sensor measured with sensors configured to 1x accumulation, 8x gain. Sensor sampling and
system processing time is included with mutually-exclusive buttons, the buzzer, slider, and touch time-outs disabled.
Figure 3.2. Current vs. Active Mode Scan Period — Base Current Consumption
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CPT112S Data Sheet
Electrical Specifications
Figure 3.3. Current vs. Active Mode Scan Period — Current Consumption for Each Additional Sensor
Note: Active mode scan period current draw measured with free run mode disabled and all 12 sensors enabled at 4x accumulation, 8x
gain. In addition, the buzzer, slider, and mutually-exclusive button groups were disabled.
Figure 3.4. Typical VOH Curves
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CPT112S Data Sheet
Electrical Specifications
Figure 3.5. Typical VOL Curves
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CPT112S Data Sheet
Functional Description
4. Functional Description
4.1 Capacitive Sensing Input
4.1.1 Introduction
The capacitive to digital converter uses an iterative, charge-timing self-capacitance technique to measure capacitance on an input pin.
Sampling is configured and controlled by settings in the non-volatile configuration profile, which can be changed through the 2-pin configuration interface.
Capacitance
Active threshold
Inactive threshold
Touch delta
Baseline
Time
Figure 4.1. Capacitive Sense Data Types
4.1.2 Touch Qualification Criteria
The device detects a touch event when an inactive (untouched) input enabled by the input enable mask detects an sequence of measurements that cross the active threshold.
The device detects a touch release event when an active (touched) input enabled by the input enable mask detects an sequence of
measurements that cross the inactive threshold.
The debounce configuration profile parameter defines how many measurements in a row must cross a threshold before a touch or release is qualified. In electrically noisy environments more heavily filtered data is used for qualification.
4.1.3 Thresholds
Capacitive sensing inputs use input-specific thresholds for touch qualification. Each input uses two thresholds, one to detect inactive-toactive transitions on the input, and another to determine active-to-inactive transitions on the input. The inputs use two thresholds to add
hysteresis and prevent active/inactive ringing on inputs. Each threshold can be set through Simplicity Studio tools and all thresholds are
stored in non-volatile memory in the device's configuration profile.
Thresholds are defined as percentages of a capacitive sensing input's touch delta.
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CPT112S Data Sheet
Functional Description
4.1.4 Debounce Counter
Each capacitive sensing input maintains its own debounce counter. For an inactive sensor, this counter tracks the number of successive samples which have crossed that input's active threshold. For an active sensor, this counter tracks the number of successive samples which have crossed the inactive threshold. When the counter reaches a terminal value defined in the the configuration profile, the
touch/release event is qualified.
4.1.5 Touch Deltas
Each capacitive sensing input uses a stored touch delta value that describes the expected difference between inactive and active capacitive sensing output codes. This value is stored in the configuration profile for the system and is used by the touch qualification engine, which defines inactive and active thresholds relative to the touch delta.
The touch deltas are stored in the configuration profile in a touch delta/16 format. For this reason, touch deltas must be configured as
multiples of 16.
4.1.6 Auto-Accumulation and Averaging
Capacitive sensing inputs have an auto-accumulate and average post-sample filter that can be used to improve signal strength if needed. Settings stored in the configuration profile can configure the engine to accumulate 1, 4, 8, 16, 32, or 64 samples. After the defined
number of samples have been accumulated, the result is divided by either 1, 4, 8, 16, 32, or 64, depending on the accumulation setting.
This auto-accumulated and averaged value is the sample output used for all touch qualification processing. Note that sample time per
sensor increases as the level of accumulation increases. To reduce current consumption, the engine should not be set to auto-accumulate unless it is required to achieve acceptable signal strength due to thick overlays or other system-level factors.
4.1.7 Drive strength
The drive strength of the current source used to charge the electrode being measured by the capacitive sensing input can be adjusted
in integer increments from 1x to 8x (8x is the default). High drive strength gives the best sensitivity and resolution for small capacitors,
such as those typically implemented as touch-sensitive PCB features. To measure larger capacitance values, the drive strength should
be lowered accordingly. The highest drive strength setting that yields capacitive sensing output which does not saturate the sensing
engine when the electrode is active (touched) should always be used to maximize input sensitivity.
4.1.8 Active Mode Scan Enable
Active mode scanning of capacitive sensing inputs is controlled by an enable setting for each capacitive sensing input. This setting is
stored in the configuration profile.
4.1.9 Active Mode Scan Period
The capacitive sensing input engine stays in active mode whenever one or more inputs have qualified as active. During this time, the
sensors scan at a periodicity defined by the active mode scan period, which is stored in the configuration profile. Every active mode
scan pushes new samples through the processing engine, which checks for new touch and release events on all enabled inputs.
If free run mode is enabled, the engine will repeatedly scan all enabled inputs during the active mode scan period. In this mode of
operation, the active mode scan period is used as a timer to determine how much time has passed since the last qualified active sensor
has been seen. When a defined amount of time without a qualified touch event has occurred, the engine switches to a low power mode
using the sleep mode scan period, and conserves current.
If free run mode is disabled, the engine will enter a low power state after completing one scan of all enabled inputs and processing the
resulting samples. The engine will remain in this low power state until it wakes, at a time defined by active mode scan period, to perform
another scan.
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CPT112S Data Sheet
Functional Description
4.1.10 Active Mode Scan Type
The active mode scan type, which is stored in the configuration profile, controls whether the capacitive sensing engine in active mode
will scan only once during the active mode scan period before going to sleep, or whether the engine will continue scanning as quickly
as possible during the active mode scan period, never entering a low power state.
For optimal responsiveness, the engine should be configured to run with free run mode enabled. Setting the scan mode to 'free run'
causes touch qualification on a new touch to occur as quickly as the scanning engine can convert and process samples on all sensors.
In this mode, qualification time is not bounded by active mode scan period, and is only bounded by scanning configuration factors such
as the debounce setting, the number of enabled sensors, the accumulation setting on each sensor, and the timing constraints of any
enabled component.
For optimal current draw when in active mode, the engine should be configured to use the 'one scan per period' mode setting. In this
case, touch qualification is bound by the scan period and the debounce setting of the device.
Touch Event
(t = 0 ms)
Active
process
Optimized
Active
sample
10 ms
20 ms
additional
processing
30 ms
process
debounce
count = 1
additional
processing
sample
touch
qualified
sleep
Sleep
40 ms
sleep
Figure 4.2. Timing and Current — One Sample Per Period Mode
Touch Event
(t = 0 ms)
Active
process
Optimized
Active
sample
10 ms
additional
processing
20 ms
process
debounce
count = 1
30 ms
40 ms
additional
processing
sample
touch
qualified
Sleep
Figure 4.3. Timing and Current — Free Run Mode
4.1.11 Sleep Mode Scan Period
The sleep mode scan period defines the rate at which a scan of the inputs enabled as wake-up sources are sampled. Each enabled
sensor can also be enabled as a wake-up source. After the sleep mode scan completes, the scan is processed for a qualified candidate
touch. If a candidate touch is qualified, the system wakes form sleep mode and enters active mode scanning.
The sleep mode scan period is stored in the configuration profile and is defined in units of ms.
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CPT112S Data Sheet
Functional Description
4.1.12 Active Mode and Sleep Mode Transitions
Capacitive sensing inputs will stay in active mode until no inputs detect qualified touches for a span of time defined by the counts until
sleep parameter stored in the configuration profile. The scan period of enabled inputs is defined by the active mode scan period, also
found in the configuration profile. If free run mode is enabled, the active mode sensing engine will remain awake and scanning the sensors as fast as possible. If free run mode is disabled, the engine will put itself into a low power state for the remainder of the active
mode scan period, after a scan has completed.
When in sleep mode, the sensing engine will wake at a period defined by sleep mode scan period to do a scan on sensors that have
been enabled as wakeup sources. If the engine finds a candidate touch in this state, the system reverts to active mode to continue
scanning.
Touch Delta
Note that in systems where a proximity input is selected, the sleep mode scan engine uses conversions on the proximity input instead
of sensors enabled as wakeup sources.
touch release
new touch
sleep scan sees
touch, wakes,
qualifies touch
qualified touch
release
no touch
counter = 0
no touch
counter = 1
Device Execution
t
no touch
counter = 2
...
no touch counter
= counts before
sleep
device enters
sleep
Figure 4.4. Active and Sleep Transitions
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CPT112S Data Sheet
Functional Description
4.2 I2C Event Buffer Interface
4.2.1 Introduction
The event buffer I2C interface provides an event-driven, packetized communication system describing newly qualified events generated
by the capacitive sensing input engine.
The interface provides access to a first-in-first-out buffer of data packets. When the sensing engine generates these packets and pushes them onto the buffer. The interface then signals a host to indicate that one or more packets are available in the buffer by activating
the event buffer interrupt pin.
The interrupt pin is defined as active-low and operates as a push-pull digital output.
The host reads the packets through an I2C interface, with the host acting as an I2C master. Once all packets have been fully transmitted across the I2C interface, the event buffer interrupt pin is de-activated. The device will remain in active mode until no packets remain
in the buffer, even if no sensors have been qualified as active for the period of time defined by the active mode scan period and the
counts before sleep value.
4.2.2 Packet Retrieval
Event buffer access mode enables the host to retrieve host data structures from the device using a master read transaction. Transfers
in this mode should be made in 3-byte multiples to retrieve the entire event buffer structure.
Once the host reads the last byte of one event, that event is popped from the buffer. If only a part of the event is read, the event will
stay in the buffer and will be transmitted again by the device during the next read.
If the event buffer is read when no events have been pushed into the buffer for access, the bytes retrieved during a master read transaction across I2C will return 3 bytes of 0xFF padding.
If the interrupt pin goes active during a transaction where the transmission of these 3 bytes of padding are being sent, the 3 bytes of
padding will complete their transfer before a valid event will transmit.
If the I2C master sends a stop condition on the bus before the entire three-byte packet has been read, the device will not pop the packet from its internal buffer. Instead, the I2C state machine will reset, and the next transaction will begin with the first byte of the same
event that was being read in the previous, prematurely-terminated transaction.
The I2C event buffer has a depth of 22 events. If the host does not read events promptly after seeing the interrupt pin go active, there is
the possibility of a buffer overflow. In the event of an overflow, the I2C engine will discard the oldest events first.
New I2C packets will only be generated at the active mode sample rate, and so the buffer will only fill at a maximum of 12 packets (in
the case of 12 simultaneous touch/releases) per sample period. If the host runs the I2C bus at 400kHz and reads packets as soon as
the interrupt pin activates, all packets can be read from the buffer in 1 to 2 ms, which is faster than the rate at which a new active mode
scan sequence can complete.
The configuraion profile includes an I2C timeout register. When enabled, this register configures the maximum duration at which packets will be stored in the I2C buffer without being read from the host. If the interrupt pin is allowed to remain active for the duration defined by the timeout register, the I2C buffer will be flushed and the interrupt pin will deactivate. This feature is useful in applications
where it is not desireable to have the device remain in active mode indefinitely.
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CPT112S Data Sheet
Functional Description
4.2.3 Event Packet Structure
Every qualified event detected by the capacitive sensing input engine generates a single packet that can be retrieved by the host processor through the event buffer I2C interface. The packet is an atomic data unit that fully describes the generated event.
Note: The bytes in the packet are transmitted MSB first.
Each packet has a standard structure that can be parsed by the host.
Table 4.1. Standard Packet Structure
Byte #
Designator
0
I2C Slave Address + read bit
1
Packet counter and event type
2
Event description (byte 1)
3
Event description (byte 2)
The packet counter is a 4-bit number stored in the upper bits of byte 1. Each new event will be assigned a counter value that is +1 from
the last qualified event. After event 15, the counter wraps back to 0 for the next event. The counter captures the temporal nature of
touch events so that a host can reconstruct a sequence of events over time. Also, the host can use the counter value to determine if a
packet has been lost due to a buffer overflow.
The event type is a 4-bit value describes the originator of the event. For instance, the source could be a capacitive sensing button. The
event type is stored in the lower 4 bits of byte 1.
The event description bytes define characteristics of the event that have been qualified. Event descriptions are defined relative to the
event source. An event source that is a capacitive sensing input will have a defined set of valid event description values. Those same
values will mean something different for a different type of event source, such as a slider. Event description values are defined relative
to the event type field of byte 1.
Touch
Event
I2C Slave Address
+ read bit
byte 0
Touch
Release
Event
Slider
Event
event
type
0000
byte 1
I2C Slave Address
+ read bit
byte 0
packet
counter
0011
event
type
0001
byte 1
I2C Slave Address
+ read bit
byte 0
packet
counter
0010
packet
counter
0100
event
type
0010
byte 1
CSxx index
reserved
byte 2
byte 3
CSxx index
reserved
byte 2
byte 3
slider position
(MSB)
slider position
(LSB)
byte 2
byte 3
Figure 4.5. I2C Event Buffer Packet Structure
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CPT112S Data Sheet
Functional Description
4.2.4 Defined Event Types
The device assigns the following event types to events.
Table 4.2. Event Type Mapping
Event Type Value
Mapping
0
Sensor activity - touch event
1
Sensor activity - release event
2
Slider activity
Note that this event type value is stored in the lower 4 bits of the first byte of a packet. The upper 4 bits are a packet counter value.
4.2.5 Description Bytes for Touch Events
A touch or release event uses only one byte of the description field. That field identifies which sensor caused the touch or release event
as shown below.
Table 4.3. Touch or Release Event Sensor Mapping
Value
Mapping
0
Capacitive sensing input 0
1
Capacitive sensing input 1
2
Capacitive sensing input 2
3
Capacitive sensing input 3
4
Capacitive sensing input 4
5
Capacitive sensing input 5
6
Capacitive sensing input 6
7
Capacitive sensing input 7
8
Capacitive sensing input 8
9
Capacitive sensing input 9
10
Capacitive sensing input 10
11
Capacitive sensing input 11
4.2.6 Description Bytes for Slider Events
The slider activity description field uses two bytes to describe the position of the slider, which can be any value between 0 (0x0000) and
65534 (0xFFFE). The most-significant byte of this value is transmitted in the first byte (byte 2 of the event packet), and the least-significant byte is transmitted second (byte 3 of the event packet).
When the slider is released, a final slider event will be transmitted with 0xFFFF in the two-byte field.
4.2.7 Event Buffer I2C Slave Address
The device's I2C slave address is configurable through the configuration profile. The device will ACK its slave address only when the
interrupt pin is low, signalling that a packet is ready to be read by the host. If the interrupt pin is logic high, the device will not ACK its
slave address.
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CPT112S Data Sheet
Functional Description
4.3 Capacitive Proximity Sensing
4.3.1 Wake on Proximity
The wake on capacitive proximity detection engine monitors for the presence of a conductive object such as a hand to move within
detectable range of the sensor. When the engine detects an object, the device wakes from sleep and can begin qualifying touch events
on all sensors enabled for active mode sensing.
4.3.2 Proximity Configuration
The proximity sensing feature uses a single sensor input for proximity qualification. The configuration profile stores the pin chosen by
the user. The sensor used for proximity qualification should also have a drive strength setting that is as high as possible without saturating the input when no conductive object is in proximity to the proximity sensor. The accumulation setting of the input is also configurable.
The proximity threshold controls the sensitivity of the input. A lower threshold setting increases sensitivity and increases the range of
the sensor.
A proximity sensing input cannot be used for touch qualification, and so the active and inactive thresholds are not used for proximity
sensors. Additionally, the proximity input has no effect on other components of the device such as mutually exclusive button groups,
buzzer output, touch time out timers, and sliders.
4.4 Slider
The device supports creation of a single slider that is composed of two or more capacitive sensing input pins. The pins chosen as slider
inputs are assigned to the slider feature through the configuration profile.
The configuration profile also stores a value designated as the highest positional value that can be derived by the slider engine. That
highest value is used to derive the values of all intermediate positions on the slider array.
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CPT112S Data Sheet
Functional Description
When a capacitive sensing input pin is designated as a slider input, it will no longer function as a 'button' input and will not generate
button style touch/release events across the I2C buffer interface.
Touching the slider pads and moving a finger along a slider pad generates an event packet of type Slider, with the remaining two bytes
of the packet describing the calculated active position of the slider.
The range of possible reported slider active positions can be 0 to the maximum value of the slider as defined in the configuration profile,
which can be any value between 40 and 65534. The 65535 (0xFFFF) value is reserved for a slider untouched event.
Position 0 is always assigned to the lowest CSxx sensor enabled as a slider input. The maximum position value of the slider is assigned
to the highest CSxx sensor enabled as a slider input. All slider inputs in between are assumed to be routed to the slider contiguously,
lowest to highest.
Valid
Configuration
CS00
CS02
CS04
CS05
increasing slider
position
Valid
Configuration
CS03
CS02
CS01
CS00
CS01
CS03
increasing slider
position
Invalid
Configuration
CS00
CS02
Figure 4.6. Slider Behavior and Layout Constraints
Slider touch qualification uses the same touch deltas and thresholds that are defined in the configuration profile for all enabled sensors.
The user should configure slider sensors through the configuration profile, just as one would configure a sensor assigned to a capacitive button.
For optimal performance, each sensor used in the slider should have roughly the same touch surface area dimensions.
If the touch-timeout feature is enabled, slider-assigned inputs will also be subject to being qualified as releases by the touch-timeout
feature.
The mutually exclusive button grouping feature does not affect slider-assigned sensors. Even if the mutually exclusive button grouping
feature is enabled, multiple slider-assigned sensors can still be used to resolve a finger's position on the slider.
4.5 Touch Time-Out
The touch time-out feature can be enabled and disabled through the configuration profile. When enabled, the device will monitor touch
event duration on each input independently.
When a touch event exceeds a duration specified in the configuration profile, the device forces a release event, even if the user is still
actively touching the sensor.
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CPT112S Data Sheet
Functional Description
The feature qualifies a touch release by adding the configured touch delta value for that sensor to the sensor's current baseline value.
By doing this, the raw data-to-baseline delta created by the touch will be removed, and the touch qualification engine will see this as a
touch release event.
When the user removes a finger from a sensor that had been qualified active but has been qualified released through touch timeout, the
resulting raw-to-baseline negative delta will be aggressively tracked downward by the baseline, resulting in a sensor that remains sensitive to successive touches.
The touch timeout duration is configured globally, so all inputs are monitored for the same touch duration.
If both the touch timeout feature and the mutually exclusive button group feature are enabled, the timeout timer will only run on the
touch that is externally reported as being active.
4.6 Buzzer Output
4.6.1 Introduction
The buzzer output engine produces a square wave of a configurable duration and frequency when a capacitive sensing input goes from
inactive to active. The feature can be enabled and disabled through the configuration profile. The configuration profile also includes the
settings for active duration and frequency.
Device Execution
Active
process
Optimized
Active
sample
additional
processing
process
additional
processing
sample
sleep
Sleep
sleep
No Touch, Buzzer Inactive
Figure 4.7. Effects of the Buzzer on Current Draw — Active Mode, No Touch, Buzzer Inactive
Device Execution
process
Active
sample
additional
processing
sleep
(stall)
process
sample
additional
processing
sleep
(stall)
Optimized
Active
Sleep
Touch Detected, Buzzer Active
Figure 4.8. Effects of the Buzzer on Current Draw — Active Mode, Touch Detected, Buzzer Active
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Preliminary Rev. 0.1 | 22
CPT112S Data Sheet
Functional Description
4.6.2 Buzzer Configuration
When enabled, buzzer output will appear on the CS11/buzzer pin (pin 10) of the device. When buzzer output is enabled, CS11 is not
available for capactive input sensing.
When activated, the buzzer will remain active for either the duration specified in the configuration profile, or until the last active sensor
has qualified a touch release.
The configuration profile supports configuration of output frequencies ranging from 1 kHz to 4 kHz.
The configuration profile can configure the buzzer output pin to either push pull mode or open drain mode.
4.7 Mutually Exclusive Buttons
When enabled through the configuration profile, this system allows one and only one capacitive sensing input to be qualified as active
at a time. The first sensor active will remain the only sensor active until released. The device will internally qualify multiple touch and
release events but will not report them.
If multiple sensors have been internally qualified as active, the first sensor's touch event will be reported. If a touch event occurs simultaneously on more than one sensor, the touch with the highest touch delta will be reported.
If two sensors are qualified as active and the sensor being reported as active qualifies a touch release, the device will report that release and then report a touch qualification on the still-active second sensor.
In the case where a device has simultaneously qualified more than two active sensors and the reported active sensor qualifies and
reports a release, the remaining qualified sensor with the highest sensor name will then be reported. For example, if sensors CS00,
CS01, and CS02 are active with CS00 externally reported as active, after CS00's release, CS02 would be externally reported as an
active sensor unless the device has already qualified a touch release on CS02.
If both the touch timeout feature and the mutually exclusive button group feature are enabled, the timeout timer will only run on the
touch that is externally reported as being active.
CS00
CS01
CS02
Device Execution
physical touch on pad
touch reported by CPT device
release reported by CPT device
Figure 4.9. Mutually-Exclusive Button Operation
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Preliminary Rev. 0.1 | 23
CPT112S Data Sheet
Functional Description
4.8 Self Testing
4.8.1 Introduction
When the self-test feature is enabled through the configuration profile, the device performs a check on all enabled capacitive sensing
inputs upon startup to determine whether the sensing input pins are erroneously shorted to ground or supply. If a short or open is found
on a sensor, the self test feature will signal that an error has been found through a port pin. The feature will then disable that sensor
before beginning touch qualification scans on all sensors left enabled.
4.8.2 Test Failure Signaling
If the self test check reveals an error, the device will toggle the I2C buffer interrupt pin at a frequency of 2 Hz. This toggling will persist
for two seconds if the device detects one or more self test errors.
4.9 Configuration Profile
The configuration interface is used by the device to configure default values and performance characteristics that effect capacitive
sensing. The configuration data can be programmed through the Configuration interface (Config Clk and Config Data pins) using [Configurator] in Simplicity Studio.
Several configuration profile templates are available in Simplicity Studio to provide a starting point for development.
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Preliminary Rev. 0.1 | 24
CPT112S Data Sheet
Pin Definitions
RSTb /
Config Clk
5
Config Data
6
CS02
CS03
CS04
CS05
19
18
17
(Top View)
GND
10
4
16
CS06
15
CS07
14
CS08
13
CS09
12
GND
11
CS10
CS11 /
BUZZER
VDD
20 pin QFN
9
3
EB_SDA
GND
8
2
EB_SCL
CS00
7
1
EB_INT
CS01
20
5. Pin Definitions
Figure 5.1. CPT112S Pinout
Table 5.1. Pin Definitions for CPT112S-QFN20
Pin
Pin Name
Description
CS01
Analog input
Number
1
Capactive sensing input 1
2
CS00
Analog input
Capacitive sensing input 0
3
GND
Ground
4
VDD
Supply power input
5
RSTb /
Active-low reset /
Config Clk
Configuration clock
Config Data
Configuration data
6
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Preliminary Rev. 0.1 | 25
CPT112S Data Sheet
Pin Definitions
Pin
Pin Name
Description
EB_INT
Push-pull digital output
Number
7
Event buffer interrupt pin
8
EB_SCL
Open drain digital output
Event buffer I2C SCL
9
EB_SDA
Open drain digital input
Event buffer I2C SDA
10
11
CS11 /
Analog input, capacitive sensing input 11
Buzzer
Digital output for buzzer
CS10
Analog input
Capacitive sensing input 10
12
GND
Ground
13
CS09
Analog input
Capacitive sensing input 9
14
CS08
Analog input
Capacitive sensing input 8
15
CS07
Analog input
Capacitive sensing input 7
16
CS06
Analog input
Capacitive sensing input 6
17
CS05
Analog input
Capacitive sensing input 5
18
CS04
Analog input
Capacitive sensing input 4
19
CS03
Analog input
Capacitive sensing input 3
20
CS02
Analog input
Capacitive sensing input 2
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Preliminary Rev. 0.1 | 26
CPT112S Data Sheet
QFN20 Package Specifications
6. QFN20 Package Specifications
6.1 QFN20 Package Dimensions
Figure 6.1. QFN20 Package Drawing
Table 6.1. QFN20 Package Dimensions
Dimension
Min
Typ
Max
A
0.50
0.55
0.60
A1
0.00
—
0.05
b
0.20
0.25
0.30
b1
0.275
0.325
0.375
D
D2
3.00 BSC
1.6
1.70
e
0.50 BSC
e1
0.513 BSC
E
3.00 BSC
1.80
E2
1.60
1.70
1.80
L
0.35
0.40
0.45
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Preliminary Rev. 0.1 | 27
CPT112S Data Sheet
QFN20 Package Specifications
Dimension
Min
Typ
Max
L1
0.00
—
0.10
aaa
—
0.10
—
bbb
—
0.10
—
ddd
—
0.05
—
eee
—
—
0.08
Note:
1. All dimensions shown are in millimeters (mm) unless otherwise noted.
2. Dimensioning and Tolerancing per ANSI Y14.5M-1994.
3. This drawing is based upon JEDEC Solid State Product Outline MO-248 but includes custom features which are toleranced per
supplier designation.
4. Recommended card reflow profile is per the JEDEC/IPC J-STD-020 specification for Small Body Components.
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Preliminary Rev. 0.1 | 28
CPT112S Data Sheet
QFN20 Package Specifications
6.2 QFN20 PCB Land Pattern
Figure 6.2. QFN20 PCB Land Pattern Drawing
Table 6.2. QFN20 PCB Land Pattern Dimensions
Dimension
Min
Max
C1
2.70
C2
2.70
C3
2.53
C4
2.53
E
0.50 REF
X1
0.20
0.30
X2
0.24
.034
X3
1.70
1.80
Y1
0.50
0.60
Y2
0.24
0.34
Y3
1.70
1.80
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Preliminary Rev. 0.1 | 29
CPT112S Data Sheet
QFN20 Package Specifications
Dimension
Min
Max
Note:
1. All dimensions shown are in millimeters (mm) unless otherwise noted.
2. Dimensioning and Tolerancing is per the ANSI Y14.5M-1994 specification.
3. This Land Pattern Design is based on the IPC-7351 guidelines.
4. All metal pads are to be non-solder mask defined (NSMD). Clearance between the solder mask and the metal pad is to be 60 µm
minimum, all the way around the pad.
5. A stainless steel, laser-cut and electro-polished stencil with trapezoidal walls should be used to assure good solder paste release.
6. The stencil thickness should be 0.125 mm (5 mils).
7. The ratio of stencil aperture to land pad size should be 1:1 for the perimeter pads.
8. A 2x2 array of 0.75 mm openings on a 0.95 mm pitch should be used for the center pad to assure proper paste volume.
9. A No-Clean, Type-3 solder paste is recommended.
10. The recommended card reflow profile is per the JEDEC/IPC J-STD-020 specification for Small Body Components.
6.3 QFN20 Package Marking
112S
TTTT
YWW+
Figure 6.3. QFN20 Package Marking
The package marking consists of:
• 112S – The part number designation.
• TTTT – A trace or manufacturing code. The first letter of this code is the hardware revision.
• Y – The last digit of the assembly year.
• WW – The 2-digit workweek when the device was assembled.
• + – Indicates the device is RoHS-compliant.
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Preliminary Rev. 0.1 | 30
CPT112S Data Sheet
Relevant Application Notes
7. Relevant Application Notes
The following Application Notes are applicable to the CPT112S devices:
• AN957: TouchXpress™ Configuration and Profiling Guide — This application note guides developers through the evaluation and
configuration process of TouchXpress devices using Simplicity Studio [Xpress Configurator] and [Capacitive Sense Profiler].
• AN447: Printed Circuit Design Notes for Capacitive Sensing Performance — This document describes hardware design guidelines
specifically for capacitive sensing applications, including button placement and other layout guidelines.
• AN949: TouchXpress™ Programming Guide — This application note discusses the production programming options available for
TouchXpress devices.
Application Notes can be accessed on the Silicon Labs website (www.silabs.com/interface-appnotes) or in Simplicity Studio using the
[Application Notes] tile.
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Preliminary Rev. 0.1 | 31
Table of Contents
1. Feature List and Ordering Information . . . . . . . . . . . . . . . . . . . . . . 1
2. Typical Connection Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1 Signal, Analog, and Power connections .
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2.2 Configuration .
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3. Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1 Electrical Characteristics . . . . .
3.1.1 Recommended Operating Conditions
3.1.2 Power Consumption . . . . . .
3.1.3 Reset and Supply Monitor . . . .
3.1.4 Configuration Memory . . . . .
3.1.5 Capacitive Sense . . . . . . .
3.1.6 Buzzer Output . . . . . . . .
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3.2 Thermal Conditions .
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3.3 Absolute Maximum Ratings .
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3.4 Typical Performance Curves .
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4. Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
4.1 Capacitive Sensing Input . . . . . . .
4.1.1 Introduction . . . . . . . . . . .
4.1.2 Touch Qualification Criteria . . . . . .
4.1.3 Thresholds . . . . . . . . . . .
4.1.4 Debounce Counter . . . . . . . .
4.1.5 Touch Deltas . . . . . . . . . .
4.1.6 Auto-Accumulation and Averaging . . .
4.1.7 Drive strength . . . . . . . . . .
4.1.8 Active Mode Scan Enable . . . . . .
4.1.9 Active Mode Scan Period . . . . . .
4.1.10 Active Mode Scan Type . . . . . .
4.1.11 Sleep Mode Scan Period . . . . . .
4.1.12 Active Mode and Sleep Mode Transitions
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.13
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4.2 I2C Event Buffer Interface . . . .
4.2.1 Introduction . . . . . . . .
4.2.2 Packet Retrieval . . . . . .
4.2.3 Event Packet Structure . . . .
4.2.4 Defined Event Types . . . . .
4.2.5 Description Bytes for Touch Events
4.2.6 Description Bytes for Slider Events
4.2.7 Event Buffer I2C Slave Address .
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.17
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4.3 Capacitive Proximity Sensing.
4.3.1 Wake on Proximity . . .
4.3.2 Proximity Configuration . .
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4.4 Slider .
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.21
Table of Contents
32
4.6 Buzzer Output . . . .
4.6.1 Introduction . . . .
4.6.2 Buzzer Configuration .
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.22
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.23
4.7 Mutually Exclusive Buttons
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.23
4.8 Self Testing . . . .
4.8.1 Introduction . . . .
4.8.2 Test Failure Signaling
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.24
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4.9 Configuration Profile.
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.24
5. Pin Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
6. QFN20 Package Specifications. . . . . . . . . . . . . . . . . . . . . . . .
27
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6.1 QFN20 Package Dimensions
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6.2 QFN20 PCB Land Pattern
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6.3 QFN20 Package Marking .
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.30
7. Relevant Application Notes . . . . . . . . . . . . . . . . . . . . . . . . .
31
Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
Table of Contents
33
Simplicity Studio
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Disclaimer
Silicon Laboratories intends to provide customers with the latest, accurate, and in-depth documentation of all peripherals and modules available for system and software implementers
using or intending to use the Silicon Laboratories products. Characterization data, available modules and peripherals, memory sizes and memory addresses refer to each specific
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