Note that PA0 is also connected to ARDUINO
®
and ST morpho connectors as GPIO, depending on the use case
that can generate conflict with B1. In this case, it possible to remove the connection of B1 (SB11 OFF).
Table 8.
I/O configuration for the physical user interface
Name
I/O
Wake-up available
B1 USER1 push-button
PA0
WKUP1
B2 USER2 push-button
PE4
-
B3 USER3 push-button
PA6
-
7.7
RF I/O stage
The RF output stage is configured by default to use a PCB antenna. Nevertheless, for laboratory characterization,
it is possible to use an SMA connector (not fitted by default).
shows the RF output stage schematic. On the I/O pin, a specific component manufactured by
STMicroelectronics allows to match the pin to 50 Ω and embeds a low pass filter which allows satisfying the
certification requirements.
Figure 14.
RF I/O stage
The components C36, L1, and C37 build the matching network of the PCB antenna. The footprint couple R1 and
R5 allows switching the direction of the RF I/O. If R1 is ON (default), the PCB antenna is used. If the 0 Ω resistor
presents on the R1 footprint is moved on the R5 footprint the SMA direction is used. C39, R13, and C40 are
available footprints to build a matching network for an external antenna. By default, the connection to SMA is
direct without matching network). R13 is 0 Ω resistor, C39 and C40 are OFF.
UM2823
RF I/O stage
UM2823
-
Rev 1
page 21/37
