User's Guide

5.1 Digital Interfaces 25
5.1 Digital Interfaces
Interfaces such as SPI, UART, I2C etc. can be multiplexed to any GPIO pin which gives flexibility
with sensor connection. By default P1_4 and P1_6 are used as UART console interface by MarchX
firmware.
5.2 Analog Interfaces
Pins P1_3, P1_4, P0_7, SWD_IO and SWD_CLK can be used as analog inputs to internal ADC
converter. In order to use SWD pins as analog inputs the programming and debug function of these
pins has to be disabled first in the software. It is advisable to implement some delay between reset
and disabling SWD function so the debug function can be entered after hardware reset.
Pins P1_6 and P1_4 can be also used as temperature sensing pins for battery charging and
protection. Please refer to Dialog Semiconductor DA14680 datasheet for more details.
5.3 Programming Interface
The main programming interface is Serial Wire Debug (SWD) interface comprising of SWD_IO,
SWD_CLK and optionally Reset. Additionally it is possible to use pins P1_3 and P2_3 to commu-
nicate with internal bootloader as described in UM-B-041 Production Line Tool User Manual by
Dialog Semiconductors. This interface can be used with Dialog software and Production Line Tool
to perform firmware flashing and production testing.
5.4 Antenna connection
The MX1721 Core module has been tested and certified with MatchX MX1733 Development board
(Dev Kit). The Dev Kit is using two SMA connectors to connect external dipole antennas and two
U.FL connectors to connect RF signal from Core module. The connection is shown on Figure 5.2.
To connect the Core module to the antenna port two coaxial U.FL to U.FL pigtail cables of the length
of 43mm are used (shown on Figure 5.3).
Between U.LF and SMA connectors on the Dev kit there are few passive components for
matching and ESD protection. The detailed schematic can be seen on Figure 5.4 and layout on
Figure 5.5 (the details about the Dev Kit boards, together with schematics and gerber files can be
found on the company websites www.matchx.io ). All inductors, capacitors, resistors and ESD
components have 0402 size. The matching circuit has been designed in the way to match the antenna
to 50Ohm impedance.