LEA-M8S / LEA-M8T - Hardware integration manual
UBX-15030060 - R06
Hardware description
Page 9 of 33
Production information
1.5.4
D_SEL: Interface select (LEA-M8T only)
The D_SEL pin selects the available interfaces. SPI cannot be used simultaneously with UART/DDC.
If open, UART and DDC are available. If pulled low, the SPI interface is available. See the NEO / LEA-
M8T Data sheet [2].
1.5.5
Antenna open circuit detection (ANT_DET_N)
ANT_DET_N on EXTINT1 PIO14 is an input pin used to report whether an external circuit has detected
an external antenna or not.
"low" = Antenna detected (antenna consumes current)
"high" = Antenna not detected (no current drawn). This functionality is by default disabled.
For more information, see section 2.4.4.
Antenna supervision is configurable using message UBX-CFG-ANT.
☞
Refer to the u-blox 8 / u-blox M8 Receiver Description Including Protocol Specification Error!
eference source not found. for information about further settings.
1.5.6
TIMEPULSE
A configurable time pulse signal is available on LEA-M8S and LEA-M8T. By default, the time pulse
signal is configured to one pulse per second. For more information, see the u-blox 8 / u-blox M8
Receiver Description Including Protocol Specification [3].
1.5.7
TIMEPULSE 2 (LEA-M8T only)
A configurable TIMEPULSE2 signal is available on LEA-M8T module only. For more information see
the u-blox 8 / u-blox M8 Receiver Description Including Protocol Specification [3].
1.6
Electromagnetic interference on I/O lines
Any I/O signal line with a length greater than approximately 3 mm can act as an antenna and may pick
up arbitrary RF signals, transferring them as noise into the GNSS receiver. This specifically applies to
unshielded lines, in which the corresponding GND layer is remote or missing entirely, and to lines close
to the edges of the printed circuit board.
If, for example, a cellular signal radiates into an unshielded high-impedance line, it is possible to
generate noise in the order of volts and not only distort receiver operation but also damage it
permanently. On the other hand, noise generated at the I/O pins will emit from unshielded I/O lines.
Receiver performance may be degraded if this noise is coupled to the GNSS antenna (see Figure 18).
To avoid interference by improperly shielded lines, it is recommended to use resistors (e.g. R>20
),
ferrite beads (for example, BLM15HD102SN1) or inductors (for example, LQG15HS47NJ02) on the
I/O lines in series. Choose these components with care because they will also affect the signal rise
times.
Figure 3 shows an example of EMI protection measures on the RX/TX line using a ferrite bead. More
information can be found in section 4.3.