ST STM32 NUCLEO-F042K6 User manual

October 2015 DocID028406 Rev 1 1/31
1
UM1956
User manual
STM32 Nucleo-32 boards
Introduction
The STM32 Nucleo-32 board (NUCLEO-F031K6, NUCLEO-F042K6, NUCLEO-F303K8,
NUCLEO-L031K6) provides an affordable and flexible way for users to try out new concepts
and build prototypes with STM32 microcontrollers, choosing from the various combinations
of performance, power consumption and features. The Arduino Nano connectivity support
makes it easy to expand the functionality of the Nucleo-32 open development platform with
a wide choice of specialized shields. The STM32 Nucleo-32 board does not require any
separate probe as it integrates the ST-LINK/V2-1 debugger/programmer. The Nucleo-32
board comes with the STM32 comprehensive software HAL library together with various
packaged software examples, as well as direct access to mbed online resources at
http://mbed.org.
Figure 1. STM32 Nucleo-32 board
1. Picture not contractual
www.st.com

Contents UM1956
2/31 DocID028406 Rev 1
Contents
1 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 Product marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4 Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5 Quick start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1 Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2 System requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6 Hardware layout and configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1 Embedded ST-LINK/V2-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1.1 Drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1.2 ST-LINK/V2-1 firmware upgrade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.2 Power supply and power selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.2.1 Power supply input from USB connector . . . . . . . . . . . . . . . . . . . . . . . . 15
6.2.2 External power supply inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
VIN or +5V power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
+3V3 power supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
6.2.3 External power supply output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.3 LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.4 Push button . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.5 JP1 (IDD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.6 OSC clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.7 USART virtual communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.8 Solder bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.9 Arduino Nano connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7 Electrical schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Appendix A Mechanical dimensions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

DocID028406 Rev 1 3/31
UM1956 Contents
3
8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

List of tables UM1956
4/31 DocID028406 Rev 1
List of tables
Table 1. Ordering information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table 2. ON/OFF conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 3. SB1 configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Table 4. External power sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Table 5. OSC clock configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Table 6. Virtual communication configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 7. Solder bridges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 8. Arduino Nano connectors on NUCLEO-F031K6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 9. Arduino Nano connectors on NUCLEO-F042K6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Table 10. Arduino Nano connectors on NUCLEO-F303K8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Table 11. Arduino Nano connectors on NUCLEO-L031K6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Table 12. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

DocID028406 Rev 1 5/31
UM1956 List of figures
5
List of figures
Figure 1. STM32 Nucleo-32 board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 2. Hardware block diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 3. Top layout view of the Nucleo-32 board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 4. Bottom layout view of the Nucleo-32 board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure 5. USB composite device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Figure 6. NUCLEO-F031K6, NUCLEO-F042K6, NUCLEO-F303K8 pin assignment . . . . . . . . . . . . 25
Figure 7. NUCLEO-L031K6 pin assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 8. Nucleo-32 board top view. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 9. MCU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Figure 10. ST-LINK/V2-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 11. Nucleo-32 board mechanical dimensions in millimeter. . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Features UM1956
6/31 DocID028406 Rev 1
1 Features
•STM32 microcontrollers in 32-pin packages
•Extension with Arduino Nano connectivity
•mbed-enabled (http://mbed.org)
•On-board ST-LINK/V2-1 debugger/programmer
•USB re-enumeration capability, three different interfaces supported on USB:
– Virtual Com port
– Mass storage
– Debug port
•Flexible board power supply:
– USB VBUS
– External source
•Three LEDs:
– USB communication (LD1), power LED (LD2), user LED (LD3)
•Reset push button
•Supported by wide choice of Integrated Development Environments (IDEs) including
IAR™, Keil®, GCC-based IDEs (AC6: SW4STM32,...)

DocID028406 Rev 1 7/31
UM1956 Product marking
30
2 Product marking
Evaluation tools marked as "ES" or "E" are not yet qualified and therefore they are not ready
to be used as reference design or in production. Any consequences deriving from such
usage will not be at ST charge. In no event, ST will be liable for any customer usage of
these engineering sample tools as reference design or in production.
"E" or "ES" marking examples of location:
•On the targeted STM32 that is soldered on the board (for illustration of STM32 marking,
refer to the section “Package characteristics” of the STM32 datasheet at www.st.com).
•Next to the evaluation tool ordering part number, that is stuck or silk-screen printed on
the board.

Ordering information UM1956
8/31 DocID028406 Rev 1
3 Ordering information
The order codes and the respective targeted STM32 are listed in the below Table 1.
The meaning of NUCLEO-TXXXKY codification is as follows:
•TXXX describes the STM32 product line (T for F or L)
•K describes the pin count (K for 32 pins)
•Y describes the code size (8 for 64K, 6 for 32K)
The last six characters (e.g.: L031K6) of this order code, are printed on a sticker placed at
the top or bottom side of the board.
Table 1. Ordering information
Target STM32 Order code
STM32F031K6T6 NUCLEO-F031K6
STM32F042K6T6 NUCLEO-F042K6
STM32F303K8T6 NUCLEO-F303K8
STM32L031K6T6 NUCLEO-L031K6

DocID028406 Rev 1 9/31
UM1956 Conventions
30
4 Conventions
Table 2 provides the conventions used for the ON and OFF settings in the present
document.
In this document the reference is “STM32 Nucleo-32 board” for all information that is
common to all sale types.
Table 2. 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 or 0 ohm resistor
Solder bridge SBx OFF SBx connections left open

Quick start UM1956
10/31 DocID028406 Rev 1
5 Quick start
The STM32 Nucleo-32 board is a low-cost and easy-to-use development kit used to quickly
evaluate and start a development with an STM32 microcontroller in LQFP32 or UFQFPN32
package.
Before installing and using the product, accept the Evaluation Product License Agreement
that can be found at www.st.com/epla.
For more information on the STM32 Nucleo-32 board and to access the demonstration
software, visit the www.st.com/stm32nucleo webpage.
5.1 Getting started
Follow the sequence below, to configure the STM32 Nucleo-32 board and launch the
demonstration software:
•Check solder bridge position on the board, SB1 OFF, SB14 ON (internal regulator), JP1
ON (IDD) selected.
•For a correct identification of all device interfaces from the host PC and before
connecting the board, install the Nucleo USB driver, available at
www.st.com/stm32nucleo.
•Connect the Nucleo-32 board to a PC with a USB cable ‘type A to Micro-B’ through
USB connector CN1 to power the board. The red LED LD2 (PWR) and LD1 (COM) light
up and green LED LD3 blinks.
•Remove the jumper placed between D2 (CN3 pin 5) and GND (CN3 pin 4).
•Observe how the blinking frequency of the green LED LD3 changes, when the jumper
is in place or when it is removed.
•The demonstration software and several software examples on how to use the Nucleo-
32 board features, are available at www.st.com/stm32nucleo webpage.
•Develop your own application using available examples.
5.2 System requirements
•Windows (XP, 7, 8)
•USB type A to Micro-B USB cable

DocID028406 Rev 1 11/31
UM1956 Hardware layout and configuration
30
6 Hardware layout and configuration
The Nucleo-32 board is based on a 32-pin STM32 microcontroller in LQFP or UFQFPN
package.
Figure 2 illustrates the connections between the STM32 and its peripherals (ST-LINK/V2-1,
push button, LED, and Arduino Nano connectors).
Figure 3: Top layout view of the Nucleo-32 board and Figure 4: Bottom layout view of the
Nucleo-32 board show the location of these features on the Nucleo-32 board.
Figure 2. Hardware block diagram
06Y9
(PEHGGHG
67/,1.9
670
0LFURFRQWUROOHU
5(6(7
0LFUR
86%
,2 ,2
%
567
$UGXLQR1DQR
FRQQHFWRU
/('
/'
$UGXLQR1DQR
FRQQHFWRU

Hardware layout and configuration UM1956
12/31 DocID028406 Rev 1
Figure 3. Top layout view of the Nucleo-32 board
U2
STM32
Microcontroller
CN1
ST-LINK Micro B
USB connector
LD1
(Red/Green LED)
COM
LD2
(
Red LED
)
Power
B1
Reset Button
LD3
(
Green LED
)
CN2
ST-LINK SWD
connector
(reserved)
SB1
Power confi
g
uration
SB2
Connect VCP TX to ST-LINK
SB3
Connect VCP RX to ST-LINK
SB4
Connect PF0/PC14 to MCO
SB6
Connect PF0/PC14 to D8
SB5
Co
nn
ect
PF
0/
P
C
14
to
X1
SB7
Connect PF1/PC15 to X1
SB8
Connect PF1/PC15 to D7

DocID028406 Rev 1 13/31
UM1956 Hardware layout and configuration
30
Figure 4. Bottom layout view of the Nucleo-32 board
6.1 Embedded ST-LINK/V2-1
The ST-LINK/V2-1 programming and debugging tool is integrated in the Nucleo-32 board.
The ST-LINK/V2-1 makes the Nucleo-32 board mbed enabled.
The embedded ST-LINK/V2-1 supports only the SWD for STM32 devices. For information
about debugging and programming features refer to: ST-LINK/V2 in-circuit
debugger/programmer for STM8 and STM32 (UM1075 User manual), which describes in
detail all the ST-LINK/V2 features.
The new features supported by ST-LINK/V2-1 versus ST-LINK/V2 are:
•USB software re-enumeration
•Virtual com port interface on USB
•Mass storage interface on USB
•USB power management request for more than 100mA power on USB
CN4
Arduino Nano connector
CN3
Arduino Nano connector
JP1
IDD m
easu
r
e
m
e
n
t
SB14
3.3V regulator output
SB18
Connect D4 to A4
SB16
Connect D5 to A5
SB11
Connect 670 pin 16 to
GND
SB15
Connect D13 to LD3
SB17
Connect MCO to PA0
SB10
Connect VDD to 670
pin 5
SB13
Connect GND to 670 pin
32
SB12
Connect BOOT0 to GND
SB9
ST-LINK RESET

Hardware layout and configuration UM1956
14/31 DocID028406 Rev 1
The features not supported on ST-LINK/V2-1 are:
•SWIM interface
•Minimum supported application voltage limited to 3V
Known limitation:
•Activating the readout protection on the STM32 target, prevents the target application
from running afterwards. The target readout protection must be kept disabled on ST-
LINK/V2-1 boards.
The embedded ST-LINK/V2-1 is directly connected to the SWD port of the target STM32.
6.1.1 Drivers
The ST-LINK/V2-1 requires a dedicated USB driver, which, for Windows XP, 7 and 8, can be
found at www.st.com.
In case the STM32 Nucleo board is connected to the PC before the driver is installed, some
Nucleo interfaces may be declared as “Unknown” in the PC device manager. In this case
the user must install the driver files (refer to Figure 5) and from the device manager update
the driver of the connected device.
Note: Prefer using the “USB Composite Device” handle for a full recovery.
Figure 5. USB composite device
6.1.2 ST-LINK/V2-1 firmware upgrade
The 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 added, bug fixes, support for new microcontroller families), it is
recommended to visit www.st.com before starting to use the STM32 Nucleo-32 board and
periodically, to stay up-to-date with the latest firmware version.

DocID028406 Rev 1 15/31
UM1956 Hardware layout and configuration
30
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 source: VIN (7V-12V), +5V (5V) or +3V3 power supply pins on CN4. In case VIN,
+5V or +3V3 is used to power the Nucleo-32 board, this power source must comply with the
standard EN-60950-1: 2006+A11/2009, and must be Safety Extra Low Voltage (SELV) with
limited power capability.
In case the power supply is +3V3, the ST-LINK is not powered and cannot be used.
6.2.1 Power supply input from USB connector
The Nucleo-32 board and shield board can be powered from the ST-LINK USB connector
CN1. Note that only the ST-LINK part is power supplied before the USB enumeration, as
host PC only provides 100 mA to the boards at that time. During the USB enumeration, the
Nucleo-32 board requires 300 mA of current to the host PC. If the host is able to provide the
required power, the targeted STM32 microcontroller is powered and the red LED LD2 is
turned ON, thus the Nucleo-32 board and its shield can consume a maximum of 300 mA
current and not more. If the host is not able to provide the required current, the targeted
STM32 microcontroller and the shield board are not power supplied. As a consequence the
red LED LD2 stays turned OFF. In such case it is mandatory to use an external power
supply as explained in the next Section 6.2.2: External power supply inputs.
SB1 is configured according to the maximum current consumption of the board. SB1 can be
set ON to inform the host PC that the maximum current consumption does not exceed
100 mA (even when Arduino Nano shield is plugged). In such condition USB enumeration
will always succeed since no more than 100 mA is requested to the host PC. Possible
configurations of SB1 are summarized in Table 3.
Warning: If the maximum current consumption of the Nucleo-32 board
and its shield board exceed 300 mA, it is mandatory to power
the Nucleo-32 board, using an external power supply
connected to VIN, +5V or +3V3.
Note: In case the board is powered by a USB charger, there is no USB enumeration, so the LED
LD2 remains set to OFF permanently and the target STM32 is not powered. In this specific
case the SB1 must be set ON, to allow the target STM32 to be powered anyway.
Table 3. SB1 configuration
Solder bridge state Power supply Allowed current
SB1 OFF (default) USB power through CN1 300mA max
SB1 ON 100mA max
SB1 (ON/OFF) VIN, +3V3 or +5V power For current limitation refer to Table 4

Hardware layout and configuration UM1956
16/31 DocID028406 Rev 1
6.2.2 External power supply inputs
The Nucleo-32 board and its shields boards can be powered in three different ways from an
external power supply, depending on the voltage used. The three power sources are
summarized in the Ta bl e 4 .
VIN or +5V power supply
When powered from VIN or +5V, it is still possible to use ST-LINK for communication for
programming or debugging only, but it is mandatory to power the board first, using VIN or
+5V, then to connect the USB cable to the PC. By this way the enumeration will succeed
anyway, thanks to the external power source.
The following power sequence procedure must be respected:
1. Check that SB1 is OFF
2. Connect the external power source to VIN or +5V
3. Power on the external power supply 7V< VIN < 12V to VIN, or 5V for +5V
4. Check red LED LD2 is turned ON
5. Connect the PC to USB connector CN1
If this order is not respected, the board may be powered by VBUS first, then by VIN or +5V,
as the following risks may be encountered:
1. If more than 300 mA current is needed by the board, the PC may be damaged or
current supply can be limited by PC. As a consequence the board is not powered
correctly.
2. 300 mA is requested at enumeration (since SB1 must be OFF) so there is risk that
request is rejected and enumeration does not succeed if the PC cannot provide such
current. Consequently the board is not power supplied (LED LD2 remains OFF).
Table 4. External power sources
Input power
name Connector pin Voltage range Max current Limitation
VIN CN4 pin 1 7V to 12V 800mA
From 7V to 12V only and input
current capability is linked to input
voltage:
800mA input current when VIN=7V
450mA input current when
7V<VIN<9V
300mA input current when
10V>VIN>9V
less than 300mA input current when
VIN>10V
+5V CN4 pin 4 4.75V to
5.25V 500mA ST-LINK not powered
+3V3 CN4 pin 14 3V to 3.6V - ST-LINK not powered and SB14 and
SB9 must be OFF.

DocID028406 Rev 1 17/31
UM1956 Hardware layout and configuration
30
+3V3 power supply
Using the +3V3 (CN4 pin 14) directly as power input, can be interesting, for instance, in
case the 3.3V is provided by a shield board. In this case the ST-LINK is not powered, thus
programming and debug features are not available. When the board is powered by +3V3
(CN4 pin 14), the solder bridge SB14 and SB9 (NRST) must be OFF.
6.2.3 External power supply output
When powered by USB or VIN, the +5V (CN4 pin 4) can be used as output power supply for
an Arduino Nano shield. In this case, the maximum current of the power source specified in
Table 4: External power sources must be respected.
The +3.3V (CN4 pin 14) can be used also as power supply output. The current is limited by
the maximum current capability of the regulator U3 (500 mA max).
6.3 LEDs
The tricolor LED (green, orange, red) LD1 (COM) provides information about ST-LINK
communication status. LD1 default color is red. LD1 turns to green to indicate that
communication is in progress between the PC and the ST-LINK/V2-1, with the following
setup:
•Slow blinking red/off: at power-on before USB initialization
•Fast blinking red/off: after the first correct communication between PC and ST-
LINK/V2-1 (enumeration)
•Red on: when initialization between PC and ST-LINK/V2-1 is completed
•Green on: after a successful target communication initialization
•Blinking red/green: during communication with target
•Green on: communication finished and successful
•Orange on: communication failure
User LD3: the green LED is a user LED connected to Arduino Nano signal D13
corresponding to STM32 I/O PB3 (Pin 26). Refer to Table 8, Ta b l e 9 and Table 10 for
concerned STM32:
•When the I/O is HIGH value, the LED is on
•When the I/O is LOW, the LED is off
PWR LD2: the red LED indicates that the STM32 part is powered and +5V power is
available.
6.4 Push button
B1 RESET: the push button is connected to NRST, and it is used to reset the STM32.

Hardware layout and configuration UM1956
18/31 DocID028406 Rev 1
6.5 JP1 (IDD)
JP1, labeled IDD, is used to measure the STM32 microcontroller consumption by removing
the jumper and connecting an ammeter.
•JP1 ON: STM32 is powered (default).
•JP1 OFF: an ammeter must be connected to measure STM32 current.
If there is no ammeter, STM32 is not powered.
6.6 OSC clock
U2 pin 2 and pin 3 can be used as OSC clock input or can be used as Arduino Nano D8 and
D7 GPIO. There are four ways to configure the pins corresponding to different STM32
MCUs and clock usage (refer to Table 5).
Boards with STM32Lxxx are delivered with 32.768 KHz crystal (X1). Associated capacitors
and solder bridges (C12, C13, SB4 to SB8) are configured to support LSE by default.
Boards with STM32Fxxx are delivered without crystal (X1). Associated capacitors
(C12,C13) are not populated and SB4 to SB8 are configured to support HSI by default.
6.7 USART virtual communication
Thanks to SB2 and SB3, the USART interface of STM32 available on PA2 (TX) and PA15
(RX), can be connected to ST-LINK/V2-1. When USART is not used it is possible to use PA2
as Arduino Nano A7. Refer to Table 6.
Table 5. OSC clock configurations
Solder bridge
STM32 Clock configuration
SB4 SB17 SB6 SB8 SB5 and
SB7
ON OFF OFF ON OFF
STM32Fxxx
MCO from ST-LINK
connected to OSCIN
(PF0) (1)
1. In applications, where VCP is used for communication at speed higher than 9600 bauds, it may be needed
to use this solder bridge configuration, to use 8MHz clock (MCO from ST-LINK) to get a more precise
frequency.
OFF OFF ON ON OFF HSI configuration
(default configuration)
OFF ON OFF OFF OFF
STM32Lxxx
MCO from ST-LINK
connected to CKIN
(PA0)(1)
OFF OFF OFF OFF ON 32K LSE mounted on X1
(default configuration)
OFF OFF ON ON/OFF OFF All
Arduino Nano D7
connected to PF0 / PC14
OFF OFF ON/OFF ON OFF Arduino Nano D8
connected to PF1 / PC15

DocID028406 Rev 1 19/31
UM1956 Hardware layout and configuration
30
6.8 Solder bridges
Table 6. Virtual communication configuration
Bridge State
(1)
1. The default configuration is reported in bold style.
Description
SB2 OFF PA2 is connected to CN4 pin 5 as Arduino Nano Analog input A7 and
disconnected from ST-LINK USART.
ON PA2 is connected to ST-LINK as Virtual com TX (default).
SB3 OFF PA15 is not connected.
ON PA15 is connected to ST-LINK as Virtual com RX (default).
Table 7. Solder bridges
Bridge State
(1) Description
SB10 (VREF+) ON VREF+ on STM32 is connected to VDD.
OFF VREF+ on STM32 is not connected to VDD and is provided by pin
13 of CN4.
SB15 (LD3-LED) ON Green user LED LD3 is connected to D13 of Arduino Nano signal.
OFF Green user LED LD3 is not connected.
SB9 (NRST)
ON The NRST signal of ST-LINK is connected to the NRST pin of the
STM32.
OFF The NRST signal of ST-LINK is not connected to the NRST pin of the STM32, when used external power (+3V3, +5V) as power
supply.
SB11(PB2/VSS) ON Pin 16 of STM32 (U2) is connected to VSS.
OFF Pin 16 of STM32 (U2) is not connected to VSS, and used as GPIO
PB2 for STM32F031.
SB13(PB8/VSS) ON Pin 32 of STM32 (U2) is connected to VSS.
OFF Pin 32 of STM32 (U2) is not connected to VSS, and used as GPIO
PB8 for STM32F031.
SB12(PB8 /BOOT0) ON Pin 31 of STM32 (U2) is connected to GND via 10K pull-down and
used as BOOT0.
OFF Pin 16 of STM32 (U2) is not connected and is GPIO PB8 for
STM32F042.
SB16 ON STM32 PB6 is connected to CN4 pin 7 for I2C SDA support on
Arduino Nano A5. In such case STM32 PB6 does not support
Arduino Nano D5 and PA6 must configured as Input floating.
OFF CN4 pin 7 is used as Arduino Nano analog input A5 without I2C
support and CN3 pin 8 is available as Arduino Nano D5.

Hardware layout and configuration UM1956
20/31 DocID028406 Rev 1
6.9 Arduino Nano connectors
CN3 and CN4 are male connectors compatible with Arduino Nano standard. Most shields
designed for Arduino Nano can fit to the STM32 Nucleo-32 board.
Caution: The I/Os of STM32 are 3.3 V compatible instead of 5 V for Arduino Nano.
Table 8, Table 9, Table 10 and Table 11 show the pin assignments of each STM32 on
Arduino Nano connectors.
Figure 6 and Figure 7 show Arduino Nano connectors assignment for NUCLEO-F031K6,
NUCLEO-F042K6, NUCLEO-F303K8 and NUCLEO-L031K6.
SB18 ON STM32 PB7 is connected to CN4 pin 8 for I2C SCL support on
Arduino Nano A4. In such case STM32 PB7 does not support
Arduino Nano D4 and PA5 must be configured as input floating.
OFF CN4 pin 8 is used as Arduino Nano analog input A4 without I2C
support and CN3 pin 7 is available as Arduino Nano D4.
1. The default configuration is reported in bold style.
Table 7. Solder bridges (continued)
Bridge State
(1) Description
Table 8. Arduino Nano connectors on NUCLEO-F031K6
Connector Pin number Pin name STM32 pin Function
Left connector
CN3
1 D1 PA9 USART1_TX(1)
2 D0 PA10 USART1_RX(1)
3 RESET NRST RESET
4 GND - Ground
5D2PA12 -
6 D3 PB0 TIM3_CH3
7D4
(5) PB7 -
8D5
(5) PB6 TIM16_CH1N(2)
9 D6 PB1 TIM14_CH1
10 D7(3) PF0 -
11 D8(3) PF1 -
12 D9 PA8 TIM1_CH1
13 D10 PA11 SPI_CS(4) || TIM1_CH4
14 D11 PB5 SPI1_MOSI || TIM3_CH2
15 D12 PB4 SPI1_MISO
Right connector
CN4 1 VIN - Power input