ST STM32L053 User manual

September 2021 UM1775 Rev 4 1/39
UM1775
User manual
Discovery kit with STM32L053C8 MCU
Introduction
The STM32L053 Discovery kit (32L0358DISCOVERY) helps the user to discover the full
feature range of the STM32L0 Series and develop applications. It is based on the
STM32L053C8T6 microcontroller and includes an embedded ST-LINK/V2-1
debugger/programmer, linear touch sensor, touchkeys, IDD current measurement, 2.13” E-
paper display, NFC connector for the PLUG-CR95HF-B board, LEDs, push-buttons and a
USB Mini-B connector.
The STM32L053 Discovery kit comes with a comprehensive STM32 software HAL library
with various packaged software examples available in the STM32CubeL0 MCU Package,
as well as direct access to Arm®Mbed™ on-line resources at https://os.mbed.com/.
Figure 1. STM32L053 Discovery board
Picture is not contractual.
www.st.com

Contents UM1775
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Contents
1 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1 Codification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Development environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 System requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2 Development toolchains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4 Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5 Quick start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1 Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6 Hardware layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1 Embedded ST-LINK/V2-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1.1 Drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1.2 ST-LINK/V2-1 firmware upgrade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1.3 VCP configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1.4 Using ST-LINK/V2-1 to program/debug the STM32L053C8T6 on board .
15
6.1.5 Using ST-LINK/V2-1 to program/debug an external
STM32 application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.2 Power supply and power selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.2.1 Power supply input from the USB connector . . . . . . . . . . . . . . . . . . . . . 18
6.2.2 External power supply inputs: 5V_IN or USB USER CN3 . . . . . . . . . . . 19
6.3 LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.4 Pushbuttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.5 NFC connector for PLUG-CR95HF-B board . . . . . . . . . . . . . . . . . . . . . . 20
6.6 Electronic paper display (EPD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.7 JP4 (IDD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.8 BOOT0 configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.9 Linear touch sensor / touchkeys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.10 USB device support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

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UM1775 Contents
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6.11 USART configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.12 OSC clock supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.13 OSC 32 KHz clock supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.14 Solder bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.15 Extension connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7 Mechanical drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
8 32L0358DISCOVERY Discovery kit information . . . . . . . . . . . . . . . . . . 33
8.1 Product marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.2 32L0358DISCOVERY product history . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.2.1 Product identification 32L0538DISCO/ . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.2.2 Product identification DK32L0538$AU1 . . . . . . . . . . . . . . . . . . . . . . . . 34
8.3 Board revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.3.1 MB1143 revision B-01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.3.2 MB1143 revision B-03 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.4 Board known limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.4.1 MB1143 revision B-01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.4.2 MB1143 revision B-03 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Appendix A Federal Communications Commission (FCC)
and ISED Canada Compliance Statements . . . . . . . . . . . . . . . . . . . 35
A.1 FCC Compliance Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
A.1.1 Part 15.19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
A.1.2 Part 15.21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
A.1.3 Part 15.105 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
A.2 ISED Compliance Statement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Appendix B CE conformity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

List of tables UM1775
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List of tables
Table 1. Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Table 2. Codification explanation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Table 3. ON/OFF conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table 4. Jumper states . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 5. Debug connector CN5 (SWD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Table 6. NFC connector pinout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Table 7. Solder bridges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Table 8. Extension connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Table 9. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

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UM1775 List of figures
5
List of figures
Figure 1. STM32L053 Discovery board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 2. STM32L053 Discovery board hardware block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 3. Top layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 4. Bottom layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 5. Updating the list of drivers in device manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure 6. STM32L053 Discovery board connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 7. ST-LINK/V2-1 connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 8. NFC board plugged on the STM32L053 Discovery board . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 9. Jumper JP4 in position OFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 10. Jumper JP4 in position ON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 11. No Jumper on JP4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 12. STM32L053 Discovery board mechanical drawing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Features UM1775
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1 Features
The STM32L053 Discovery kit offers the following features:
•STM32L053C8T6 microcontroller with 64 Kbytes of Flash memory and 8 Kbytes of
RAM, in an LQFP48 package
•2.13" E-paper display, 122×250 pixels
•USB 2.0 FS
•One linear touch sensor or four touchkeys
•Reset and user push-buttons
•Four LEDs:
– LD1 (red/green) for USB communication
– LD2 (red) for 3.3 V power on
– Two user LEDs: LD3 (green), LD4 (red)
•IDD current measurement
•Board connectors:
– USB Mini-B connector
– NFC expansion connector for the PLUG-CR95HF-B daughterboard
– 2.54 mm pitch expansion header for direct access to various features of the
STM32L053C8T6 microcontroller and easy probing of the LQFP48 I/Os
•Flexible power-supply options: ST-LINK, USB VBUS, or external sources
•External application power supply: 3 V and 5 V
•Comprehensive free software libraries and examples available with the STM32CubeL0
MCU Package
•On-board ST-LINK/V2-1 debugger/programmer with USB re-enumeration capability:
mass storage, Virtual COM port, and debug port
•Support of a wide choice of Integrated Development Environments (IDEs) including
IAR Embedded Workbench®, MDK-ARM, STM32CubeIDE, and Mbed Studio

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UM1775 Ordering information
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2 Ordering information
To order the 32L0358DISCOVERY Discovery kit, refer to Table 1. Additional information is
available from the datasheet and reference manual of the target microcontroller.
2.1 Codification
The meaning of the codification is explained in Table 2.
Table 1. Ordering information
Order code Board reference Target STM32
STM32L0538-DISCO MB1143 STM32L053C8T6
Table 2. Codification explanation
STM32L0XXY-DISCO Description Example: STM32L0538-DISCO
STM32L0 MCU series in STM32 32-bit Arm Cortex
MCUs STM32L0 Series
XX MCU product line in the series STM32L0x3 includes the
STM32L053xx MCUs
YSTM32 Flash memory size:
– 8 for 64 Kbytes 64 Kbytes
DISCO Discovery kit Discovery kit

Development environment UM1775
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3 Development environment
3.1 System requirements
•Multi.OS support: Windows®10, Linux® (a) 64-bit, or macOS® (b)
•USB Type-A or USB Type-C®to Mini-B cable
3.2 Development toolchains
•IAR Systems - IAR Embedded Workbench® (c)
•Keil®- MDK-ARM(c) (d)
•STMicroelectronics - STM32CubeIDE
•Arm®- Mbed Studio(e) (f) (g)
4 Conventions
Table 3 provides the definition of some conventions used in the present document.
a. Linux®is a registered trademark of Linus Torvalds.
b. macOS®is a trademark of Apple Inc. registered in the U.S. and other countries.
All other trademarks are the property of their respective owners.
c. On Windows®only.
d. Free MDK-ARM for Arm®Cortex®-M0/M0+ cores.
e. Arm and Mbed are registered trademarks or trademarks of Arm Limited (or its subsidiaries) in the US and
or elsewhere.
f. Refer to the os.mbed.com website and to the “Ordering information” section to determine which order
codes are supported.
g. All other trademarks are the property of their respective owners.
Table 3. ON/OFF conventions
Convention Definition
Jumper JPx ON Jumper fitted
Jumper JPx OFF Jumper not fitted
Solder bridge SBx ON SBx connections closed by solder
Solder bridge SBx OFF SBx connections left open

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5 Quick start
The STM32L053 Discovery kit is a low-cost and easy-to-use development kit to quickly
evaluate and start a development with the STM32L053C8T6 ultra-low-power microcontroller
in the STM32L0 Series.
Before installing and using the product, accept the Evaluation Product License Agreement
from the www.st.com/stm32l0-discovery webpage.
For more information on the STM32L053 Discovery kit, visit the www.st.com/stm32l0-
discovery webpage.
5.1 Getting started
Refer to the sequence of operations described on the product packaging.

Hardware layout UM1775
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6 Hardware layout
The STM32L053 Discovery board is designed around the STM32L053C8T6 microcontroller
in a 48-pin LQFP package.
Figure 2 illustrates the connections between the STM32L053C8T6 and its peripherals (ST-
LINK/V2-1, linear touch sensor, touchkeys, IDD current measurement, 2.13” E-paper
display, NFC connector for PLUG-CR95HF-B board, LEDs, push-buttons and an USB Mini-
B connector).
Figure 3 and Figure 4 help users to locate these features on the STM32L053 Discovery
board.
Figure 2. STM32L053 Discovery board hardware block diagram
Embedded
ST-LINK/V2-1
STM32L053C8T6
I/O I/O
RESET
USB ST-LINK
Mini-B
SWDHeader
LEDs
LD3, LD4
Linear
touch sensor
NFC
connector
B2
RESET
B1
USER
IDD current
measurement
I/O
Header
MSv39739V2
E-paper display
I/O
USB USER
Mini-B

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Figure 3. Top layout
MSv34155V3
IDD measurement
(JP4)
COM
(LD1)
NFC connector
(CN1)
VCP RX, TX
(SB2, SB3)
Linear touch sensor
/
Touchkeys
3 V power
supply output
USB ST-LINK
ST-LINK/V2-1
USB USER
RX,TX
(JP3)
Reserved
(JP1)
Reserved
(JP2)
Configuration
(BOOT0)
Green LED
(LD3)
Red LED
(LD4)
User button
(B1)
Reset button
(B2)
2.13" E-paper display
(U4)
5 V power
supply input
5 V power
supply output
ST-LINK/DISCOVERY
selector (CN4)
PWR
(LD2)

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Figure 4. Bottom layout
MSv34156V3
Reserved
(SB4, 5, 6, 11)
Default
(SB7,8,9,12)
STM_RST
(SB10)
RX, TX
(SB14,15)
X2 crystal
(SB18,19)
Crystal
(X2)
MCO
(SB20)
OSC_IN
(SB21)
Touch sensor
(SB23, 24, 25, 26, 27, 28)
B2 – RESET
(SB29)
STM32L053C8T6
(U8)
B1 – USER
(SB22)
USB_USER
(SB16, 17)
NRST
(SB13)

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6.1 Embedded ST-LINK/V2-1
The ST-LINK/V2-1 programming and debugging tool is integrated on the STM32L053
Discovery board.
The embedded ST-LINK/V2-1 supports only SWD for STM32 devices.
For information about the debugging and programming features refer to the ST-LINK/V2 in-
circuit debugger/programmer for STM8 and STM32 user manual (UM1075). For a
comparison of the various ST-LINK solutions, refer to the Overview of ST-LINK derivatives
technical note (TN1235).
There are two different ways to use the embedded ST-LINK/V2-1 depending on the jumper
states (see Table 4):
•program/debug the MCU on board (Section 6.1.4).
•program/debug an MCU in an external application board using a cable connected to
SWD connector CN5 (Section 6.1.5).
6.1.1 Drivers
ST-LINK/V2-1 requires a dedicated USB driver, which, for Windows®7, Windows®8 and
Windows®10, is available from www.st.com.
In cases where the STM32L053 Discovery board is connected to the PC before the driver is
installed, some STM32L053 Discovery board interfaces might be declared as “Unknown” in
the PC device manager. In this case, the user must install the dedicated driver files and
update the driver of the connected device from the device manager, as shown in Figure 5.
Note: It is preferable to use the “USB Composite Device” handle for a full recovery.
Figure 5. Updating the list of drivers in device manager
Table 4. Jumper states
Jumper state Description
Both CN4 jumpers ON ST-LINK/V2-1 functions enabled for on board programming (default)
Both CN4 jumpers OFF ST-LINK/V2-1 functions enabled for application through external CN5
connector (SWD supported)

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6.1.2 ST-LINK/V2-1 firmware upgrade
ST-LINK/V2-1 embeds a firmware upgrade mechanism for in-situ upgrade through the USB
port. As the firmware may evolve during the life time of the ST-LINK/V2-1 product (for
example new functionalities, bug fixes, support for new microcontroller families), visiting the
www.st.com website is recommended before starting to use the STM32L053 Discovery
board, then periodically to stay up-to-date with the latest firmware version.
6.1.3 VCP configuration
ST-LINK/V2-1 supports the Virtual COM port (VCP). To enable this function, the solder
bridges SB2 and SB3 (See Figure 3: Top layout) for Mbed™ support are closed. Table 7:
Solder bridges indicates this with the ON state.

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6.1.4 Using ST-LINK/V2-1 to program/debug the STM32L053C8T6 on board
To program the STM32L053C8T6 on board, simply plug in the two jumpers on CN4, as
shown in Figure 6 in pink, but do not use the CN5 connector as that could disturb the
communication with the STM32L053C8T6 of the STM32L053 Discovery board.
Figure 6. STM32L053 Discovery board connections

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6.1.5 Using ST-LINK/V2-1 to program/debug an external
STM32 application
It is very easy to use ST-LINK/V2-1 to program an STM32 microcontroller on an external
application. Simply remove the two jumpers from CN4 as shown in Figure 7 and connect the
application to the CN5 debug connector according to Table 5.
Note: SB13, must be OFF if CN5 pin 5 (NRST) is used in the external application.
Table 5. Debug connector CN5 (SWD)
Pïn CN5 Designation
1 VDD_TARGET VDD from application
2 SWLCK SWD clock
3 GND Ground
4 SWDIO SWD data input/output
5 NRST RESET of target MCU
6SWO Reserved

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Figure 7. ST-LINK/V2-1 connections
6.2 Power supply and power selection
The power supply is provided either by the host PC through the USB cable, or by an
external 5 V power supply.
The STM32L053 Discovery board requires 300 mA from the host PC: about 90 mA are
needed by a simple E-paper demo application, 100 mA for an extension board, and 100 mA
as a safety margin.

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The D3, D4 and D6 diodes protect the 5 V pins from external power supplies:
•5 V and 3 V can be used as output power supplies when an extension board is
connected to pins P2 and P3.
In this case, the 5V_O and 3V_O pins deliver a 5 V or 3.3 V power supply and the
power consumption of the extension board must be lower than 100 mA.
•5 V can also be used as input power supply, for instance when the USB connector is
not connected to the PC (pin 5V_I of header P3).
In this case, the STM32L053 Discovery board must be powered by a power supply unit
or by an auxiliary equipment complying with standard EN-60950-1: 2006+A11/2009. It
must be Safety Extra Low Voltage (SELV) with limited power capability.
6.2.1 Power supply input from the USB connector
ST-LINK/V2-1 supports USB power management allowing the request of more than 100 mA
from the host PC.
All parts of the STM32L053 Discovery board and extension board can be powered from the
ST-LINK/V2-1 USB connector CN2 (U5V or VBUS). Note that only the ST-LINK/V2-1 part is
power supplied before the USB enumeration as the host PC only provides 100 mA to the
board at that time. During the USB enumeration, the STM32L053 Discovery board requires
300 mA from the host PC.
•If the host is able to provide the required power, the target STM32 microcontroller is
powered and the red LED LD2 is turned ON. The STM32L053 Discovery board and its
extension board can consume not more than a maximum of 300 mA.
•If the host is not able to provide the required current, the target STM32 microcontroller
and the MCU part including the extension board are not power supplied. As a
consequence the red LED LD2 remains turned OFF. In such a case, it is mandatory to
use an external power supply as explained in the next section.
Warning: If the maximum current consumption of the STM32L053 Discovery board and its
extension board exceeds 300 mA, it is mandatory to power the STM32L053 Discovery
board with an external power supply connected to 5V_IN.
Note: In cases where this board is powered by a USB charger or USB battery, there is no USB
enumeration. Therefore, LED LD1 remains OFF permanently and the target MCU is not
powered. In this specific case, the jumper JP2 must be ON to allow the target MCU to be
powered anyway. This is a special use case without enumeration and JP2 is not soldered.
To use this optional power supply, solder a 2-pin header in JP2 and set a jumper.

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6.2.2 External power supply inputs: 5V_IN or USB USER CN3
The external power source 5V_IN or USB USER CN3 is automatically detected. In this case
the current consumption of the STM32L053 Discovery board and its extension board may
exceed the allowed current on the USB. In this condition it is still possible to use the USB for
communication, for programming or debugging only, but it is mandatory to power supply the
board first using 5V_IN or USB USER CN3 then connecting the USB cable to the PC.
Proceeding this way ensures that the enumeration occurs with the support of the external
power source.
The following power sequence procedure must be respected:
1. Connect the external power source to 5V_IN or USB USER CN3.
2. Power on the external power supply 5V_IN or USB USER CN3.
3. Check that LD2 is turned on.
4. Connect the PC to USB connector CN2.
If this order is not respected, the board may be supplied by VBUS first, then by 5V_IN or USB
USER CN3. Consequently, the following risks may be encountered:
1. If more than 300 mA is needed by the board, the PC may be damaged or the current
supply can be limited by the PC. As a consequence the board is not powered correctly.
2. 300 mA is requested at enumeration (since JP2 must be OFF) so there is a risk that the
request is rejected and the enumeration does not succeed if the PC cannot provide
such current. Consequently the board is not power supplied (LED LD2 remains OFF).
6.3 LEDs
•LD1 COM:
LD1 default status is red. LD1 turns to green to indicate that communication is in
progress between the PC and ST-LINK/V2-1.
•LD2 PWR:
The red LED indicates that the board is powered.
•User LD3:
The green LED is a user LED connected to the I/O PB4 of the STM32L053C8T6.
•User LD4:
The red LED is a user LED connected to the I/O PA5 of the STM32L053C8T6.
6.4 Pushbuttons
•B1 USER:
User and Wake-Up button connected to the I/O PA0 of the STM32L053C8T6.
•B2 RESET:
The pushbutton connected to NRST is used to RESET the STM32L053C8T6.

Hardware layout UM1775
20/39 UM1775 Rev 4
6.5 NFC connector for PLUG-CR95HF-B board
A NFC (Near Field Communication) transceiver board can be connected to the STM32L053
Discovery board, for example the PLUG-CR95HF-B board.
The NFC board is plugged in connector CN1 of STM32L053 Discovery board as following:
Figure 8. NFC board plugged on the STM32L053 Discovery board