BMD-34 EVK - User guide
UBX-19033356 - R03
Hardware description
Page 10 of 20
2.5
Virtual COM port
The evaluation board allows for easy serial communication with the BMD-34 series modules
and a connected computer. The Interface IC provides a virtual COM port USB device that
connects to four GPIO pins on the module, allowing for UART communication with or without
hardware flow control. The UART lines can be completely removed from the circuit by breaking
the associated jumpers.
BMD-34 Pin Name
BMD-34 Function
Jumper
Interface IC Function
P0.05
RTS
J05
CTS
P0.06
TXD
J06
RXD
P0.07
CTS
J07
RTS
P0.08
RXD
J08
TXD
Table 2: Virtual COM port
2.6
32 kHz crystal oscillator
The evaluation board has a 32.768 kHz crystal oscillator connected to the BMD-34 module by
default. This allows the module to use any of the three available low frequency (LF) clock
sources: an internal calibrated RC oscillator, an internal synthesized clock (derived from the
32 MHz clock), or an external crystal oscillator. The external crystal oscillator is the most
accurate and lowest power LF clock option. For applications without strict time keeping
requirements, the internal calibrated RC oscillator is often suitable. The crystal is connected
to the module through a solder select jumper, allowing either the crystal or the IO header to be
connected to the module’s GPIO pins.
Figure 7: Schematic – 32 kHz crystal
2.7
NFC connector
Connection to an external NFC antenna is provided through a Molex flat-flex connector, Part
number 051281-0594. Capacitors “C2” and “C3” provide tuning of the NFC antenna for
resonance at 15.56 MHz.
Figure 8: NFC connector
