STM8-TOUCH-LIB
STM8 touch sensing library
Data brief
Features
■ Complete C source code library with firmware
examples for all STM8 microcontrollers
■ Both resistor-capacitor (RC) and charge
transfer (CT) acquisition principles supported
■ Multifunction capability to combine capacitive
sensing functions with traditional MCU features
(communications, LED/beeper/ LCD control)
■ Configuration of STM8 GPIO as touchkey
■ Flexible touchkey/wheel/slider configuration
and combination
– RC acquisition: up to 24 keys and 2
wheels/sliders supported
– CT acquisition: up to 16 keys and 2
wheels/sliders supported
■ Acquisition, filtering and calibration functions
■ Enhanced processing features for optimized
sensitivity and immunity
■ Touch-sensing user interface through firmware
API for status reporting and application
configuration
■ MCU resources
– Minimized number of external components
– Reduced MCU memory space
■ Up to 8-bit wheel/slider resolution with only
three capacitive sensing channels
■ Active shield feature
■ Compliance with MISRA
■ Compliance with Cosmic, IAR and Raisonance
C compilers
Description
STMicroelectronics STM8-TOUCH-LIB is a touch
sensing library that provides a complete robust
free source-code solution to transform any 8-bit
STM8 microcontroller into a capacitive touch
sensing controller. This solution allows designers
familiar with the use of standard microcontrollers
to create higher-end human interfaces by
replacing conventional electromechanical
switches by touch sensing keys.
The STM8 touch sensing library is part of the
application firmware. It allows combining various
capacitive sensing touchkey, wheels or sliders
with traditional MCU features (communications,
control of LEDs, beeper or LCD) in the same
application.
Two acquisition principles, RC and CT, are
available and can be configured at compiling
level. Both acquisition principles offer the same
advanced processing algorithms to filter out noise
and to compensate environmental parameters
such as temperature, humidity, and power supply
variation.
September 2010 Doc ID 17896 Rev 1 1/9
For further information contact your local STMicroelectronics sales office.
www.st.com
9
Resistor-capacitor (RC) acquisition principle STM8-TOUCH-LIB
1 Resistor-capacitor (RC) acquisition principle
The RC acquisition principle consists in measuring the charge and discharge time duration
of a RC cell made of the electrode capacitance (C
) and a load resistor (RL).
X
The RC acquisition is supported by all STM8S and STM8L microcontrollers and requires a
direct connection of the device to earth to operate properly.
The main features are the following:
● Up to 24 touchkeys distributed over 3 GPIO ports
● Up to 2 wheels or sliders with 2 different hardware implementations (5 or 8 capacitive
sensing channels)
● Capacitive sensing channels are acquired sequentially
2 Charge transfer (CT) acquisition principle
The charge transfer acquisition consists in charging the electrode capacitance (CX) and
transferring part of the accumulated charge into a sampling capacitor (C
repeated until the voltage across C
reaches a given threshold. The number of transfers
S
required to reach the threshold depends on the size of the electrode capacitance. This
acquisition principle provides a better sensitivity and robustness than RC acquisition.
). This sequence is
S
It requires a dedicated hardware composed of analog switches and STM8L MCU.
The charge transfer acquisition is only supported by STM8L101x and STM8L15x devices
since it requires a dedicated hardware composed of analog switches used to interconnect
several GPIOs which is only available on these products.
The main features are the following:
● Number touchkeys supported
– Up to 6 touchkeys on STM8L101x MCUs
– Up to 16 touchkeys on STM8L15x MCUs
● Up to 2 wheels or sliders with a single hardware implementation (3 capacitive sensing
channels)
● Number of capacitive sensing channels acquired simultaneously
– Up to 2 channels on STM8L101x MCUs
– Up to 8 channels on STM8L15x MCUs
2/9 Doc ID 17896 Rev 1
STM8-TOUCH-LIB Library architecture
CORE
-AIN3TATE
-ACHINE
!0)LAYER
+EYS3TATE
-ACHINE
!PPLICATIONLAYER
4IMEBASE
(7LAYER
3ERVICES
AI
2#ACQUISITION
34-,X
#4ACQUISITION
34-,X
#4ACQUISITION
3 Library architecture
Figure 1 shows the STM8-TOUCH-LIB firmware layers.
Figure 1. STM8-TOUCH-LIB architecture
Doc ID 17896 Rev 1 3/9
MCU resources STM8-TOUCH-LIB
4 MCU resources
Tab le 1 shows the STM8 peripherals that are used by the STM8-TOUCH-LIB. Care must be
taken when using them to avoid any misbehavior.
Table 1. List of STM8 peripherals used by the STM8-TOUCH-LIB
Peripheral Function Acquisition principle
GPIOs I/O control RC, CT
16-bit timer with 8-bit prescaler
(TIM2 or TIM3)
8-bit timer (TIM4)
Comparator (COMP) Charge transfer CT
Routing interface (RI) I/O control and charge transfer CT
4.1 Number of charge transfer capacitive sensing channels
measurement RC
V
IH/VIL
Generic timebase for the state
machine
RC, CT
Tab le 2 and Ta b l e 3 provide the maximum number of charge-transfer capacitive sensing
channels for the STM8L101x and STM8L15x package, respectively.
Table 2. STM8L101x resources used for CT acquisition
group
Acquisition
Group
1
Group
2
Maximum number
of channels
TSSOP20 / UFQFPN20 WFQFPN28 VFQFPN32 / LQFP32
I/O port
TSSOP pin
PB0 10 7
PB1 11 8 13 14
PD0 9 6 8 9
PD1 - - 9 10
PB2 12 9
PB3 13 10 15 16
PD2 - - 10 11
pin
UFQFPN
Number of
3
2
available
pins
channels
with one
sampling
capacitor
1 channel
with one
sampling
capacitor
Usage
2
Pin
12
14
PD3 - - 11 12
3
with 2 sampling capacitors
pins
available
Number of
channels
4
with one
sampling
capacitor
channels
4
with one
sampling
capacitor
6
with 2 sampling
capacitors
Usage
3
Pin
13
Number of
pins
available
Usage
3
channels
4
with one
sampling
capacitor
15
3
3
channels
4
with one
sampling
capacitor
6
with 2 sampling
capacitors
4/9 Doc ID 17896 Rev 1
STM8-TOUCH-LIB MCU resources
Table 3. STM8L15x resources used for CT acquisition
STM8L151 (no LCD) STM8L152 (with LCD)
WFQFPN28 WFQFPN32 / LQFP32 VFQFPN48 / LQFP48 WFQFPN32 / LQFP32 VFQFPN48 / LQFP48
Number
I/O port
Acquisition group
PA 6 -
Group
PA 5 5 5 6 5 6
1
PA 4 4 4 5 4 5
PC7 -
PC4
Group
2
PC3
PC2
Group
PD7 - 24 36
3
PD6 - 23 35
PD5 -
Group
PD4
4
PB7
PB6
Group
PB5
5
PB4
PB3
Group
PB2
6
PB1
PB0
Group
PD3
7
PD2
PD1 9
Group
PD0 8 9 20 - 20
8
PE5 - - 19 - 19
Maximum
number of
channels
of
Pin
available
pins
2
2
5
2
2
4
2
3
1
2
2
0
1
9
1
8
1
3
7
1
6
1
5
1
3
4
1
3
1
2
1
3
1
1
0
2
10 channels
with 7 sampling
capacitors
Usage
1
channel
with 1
sampling
capacitor
1
channel
with 1
sampling
capacitor
cannot
be used
for
touch
sensing
1
channel
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
1
channel
with 1
sampling
capacitor
Number
of
3
2
3
3
3
3
3
2
capacitors
Usage
2
channels
with 1
sampling
capacitor
1
channel
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
1
channel
with 1
sampling
capacitor
Pin
available
pins
6
-
29 43
28 42
27
22
21 33
20 31
19
18 29
17 28
16
15 26
14 25
13
12 23
11 22
10
14 channels
with 8 sampling
Number
of
Pin
available
pins
7
46
41
34
30
27
24
21
16 channels
with 8 sampling
capacitors
Number
Usage
2
channels
with 1
3
sampling
capacitor
2
channels
with 1
3
sampling
capacitor
2
channels
3
with 1
sampling
capacitor
2
channels
with 1
3
sampling
capacitor
2
channels
with 1
3
sampling
capacitor
2
channels
with 1
3
sampling
capacitor
2
channels
with 1
3
sampling
capacitor
2
channels
with 1
3
sampling
capacitor
of
Pin
available
pins
6
3
-
2
9
2
2
8
2
7
2
3
4
2
3
2
2
2
3
1
2
0
1
9
1
3
8
1
7
1
6
1
3
5
1
4
1
3
1
3
2
1
1
1
0
1
13 channels
with 7 sampling
capacitors
Usage
2
channels
with 1
sampling
capacitor
1
channel
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
2
channels
with 1
sampling
capacitor
cannot
be used
for
touch
sensing
Number
Pin
available
pins
7
46
43
42
41
36
35
34
33
31
30
29
28
27
26
25
24
23
22
21
16 channels
with 8 sampling
capacitors
of
Usage
2
channels
with 1
3
sampling
capacitor
2
channels
with 1
3
sampling
capacitor
2
channels
3
with 1
sampling
capacitor
2
channels
with 1
3
sampling
capacitor
2
channels
with 1
3
sampling
capacitor
2
channels
with 1
3
sampling
capacitor
2
channels
with 1
3
sampling
capacitor
2
channels
with 1
3
sampling
capacitor
Doc ID 17896 Rev 1 5/9
Memory resources STM8-TOUCH-LIB
5 Memory resources
The STM8-TOUCH-LIB size depends on the following parameters:
● Acquisition principle (RC or CT)
● C compiler and options: memory model, size or speed optimization
● Number of capacitive sensing channels used and type (touchkey or/and wheel or
slider)
For further information on memory resources for RC and CT acquisition, refer to
Section 5.1.
5.1 RC acquisition memory resources
Prerequisites
● COSMIC STM8 C Compiler 16-KByte version release 4.3.1 dated 02 July 2009
● Compiler options: +modsl0 +compact +split
● Sections counted for RAM: ZRAM_TSL_IO + ZRAM_TSL + ZRAM_TSLMCK +
RAM_TSL_IO + RAM_TSL + RAM_TSLMCK
● Sections counted for ROM: CODE_TSL_IO + CONST_TSL_IO + CONST_TSL +
CONST_TSLMCK + CODE_TSL + CODE_TSLMCK
RAM and ROM requirements
Tab le 4 gives the RAM and ROM memory space required to use the STM8-TOUCH-LIB for
RC acquisition.
Table 4. Typical RAM and ROM memory space required for RC acquisition
Configuration RAM (bytes) ROM (bytes)
STM8S207
5x single-channel keys
STM8L101x
3x single-channel keys
~120 ~2350
~90 ~2350
5.2 CT acquisition memory resources
Prerequisites
● COSMIC STM8 C Compiler 16-Kbyte version release 4.3.1 dated 02 July 2009
● Compiler options: +modsl0 +compact +split
● Sections counted for RAM: ZRAM_TSL_IO + ZRAM_TSL + ZRAM_TSLMCK +
RAM_TSL_IO + RAM_TSL + RAM_TSLMCK
● Sections counted for ROM: CODE_TSL_IO + CONST_TSL_IO + CONST_TSL +
CONST_TSLMCK + CODE_TSL + CODE_TSLMCK
6/9 Doc ID 17896 Rev 1
STM8-TOUCH-LIB Memory resources
RAM and ROM requirements
Tab le 4 gives the RAM and ROM memory space required to use the STM8-TOUCH-LIB for
CT acquisition.
Table 5. Typical RAM and ROM memory space required for CT acquisition
Configuration RAM (bytes) ROM (bytes)
STM8L101x
3x single-channel keys
STM8L15X
10x single-channel keys
STM8L15X
10x single-channel keys +
1x multichannel key
~90 ~1800
~220 ~1700
~280 ~4200
Doc ID 17896 Rev 1 7/9
Revision history STM8-TOUCH-LIB
6 Revision history
Table 6. Document revision history
Date Revision Changes
27-Sep-2010 1 Initial release.
8/9 Doc ID 17896 Rev 1
STM8-TOUCH-LIB
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