UM1690 Rev 3
15/27
UM1690
Hardware layout
26
5.5
Linear touch sensor / touch keys
To demonstrate touch sensing capabilities, the STM32F072 Discovery kit includes a linear
touch sensor, which can be used either as a 3-position linear touch sensor or as 4 touch
keys. Both functions are illustrated in the demonstration software.
3 pairs of I/O ports are assigned to the linear touch sensor / touch keys. Each pair must
belong to the same analog switch group:
•
PA2, PA3 (group 1)
•
PA6, PA7 (group 2)
•
PB0, PB1 (group 3)
To minimize the noise, these pairs are dedicated to the linear touch sensor and the touch
keys and are not connected to external headers. To design a touch sensing application,
refer to the following documentation and firmware:
•
For details concerning I/O ports, refer to the STM32F072RBT6 datasheet.
•
For information on software development, see DISCOVER application software on
www.st.com/stm32f0-discovery.
•
STM32 touch sensing library available from www.st.com/stm32f0-discovery.
5.6
USB device support
The STM32F072RBT6 MCU is also used to drive the second USB Mini-B connector (USB
USER) which allows the board to be used as a USB Device. The STM32F072 Discovery kit
can then act as a USB joystick, mouse, or other similar device. If both USBs are connected,
diodes D1 and D2 protect the board and use the power from the USB ST-LINK.
The board can be powered through this USB USER connector, in which case LED2 PWR
lights up, LED1 COM blinks and it can run an application in standalone mode.
The STM32F072RBT6 MCU controls the USB USER through PA11 and PA12.
5.7 BOOT0
configuration
BOOT0 is at level “0” through pull-down resistor R33. If the user wants to set BOOT0 at
level “1”, it can be configured by setting a jumper between P2.6 (BOOT0) and P2.5 (VDD).
This facility is offered for fast and instantaneous configuration.
Note:
If it is needed to set BOOT0 at level "1" continuously, then unsolder resistor R33 to avoid a
consumption of 6 mA while connecting pin P2.6 (BOOT0) and P2.5 (VDD) with a jumper or
with a wire.
5.8
Embedded USB Bootloader
The STM32F072 line microcontrollers embed a bootloader allowing the programming of
blanked device or the upgrade device firmware over the USB without the need of a specific
programmer. When using this Discovery kit, the STM32F072RBT6 MCU firmware can be
thus programmed through the second USB Mini-B connector (USER USB).
To program the microcontroller Flash memory using this approach, a jumper must be set
between BOOT0 (P2.6) and VDD (P2.5), and a cable connected between the USER USB