NEO-M9N - Integration manual
The NEO-M9N provides UART1, SPI, I2C and USB interfaces for communication with a host CPU.
The interfaces are configured via the configuration methods described in the applicable interface
description [
].
The following table shows the port numbers reported in the UBX-MON-COMMS messages.
Port no.
UBX-MON-COMMS portId
Electrical interface
1
0x0100
UART1
3
0x0300
USB
Table 13: Port number assignment
It is important to isolate interface pins when VCC is removed. They can be allowed to float or
they can be connected to a high impedance.
Example isolation circuit is shown below. The buffer (U1 and U2) type can be either push-pull or open
collector. The buffer needs a capacitor nearby (C1 and C2, e.g. 100 nH). A pull-up resistor (R1 and
R2, e.g. 10 kΩ) is needed if an open-collector buffer is used in a high-speed data line. The buffer must
isolate the line when the VCC is turned off, so it must be either supplied or enabled by the VCC. For
the I2C line a dual bidirectional bus buffer is needed.
Figure 10: NEO-M9N interface isolation
3.7.1 UART
A Universal Asynchronous Receiver/Transmitter (UART) port consists of an RX and a TX line. Neither
handshaking signals nor hardware flow control signals are available. The UART interface protocol
and baud rate can be configured but there is no support for setting different baud rates for reception
and transmission.
The NEO-M9N includes two UART serial ports. UART1 can be used as a host interface for
configuration, monitoring and control.
The UART RX interface will be disabled when more than 100 frame errors are detected
during a one-second period. This can happen if the wrong baud rate is used or the UART RX
pin is grounded. An error message appears when the UART RX interface is re-enabled at the
end of the one-second period.
Baud rate
Data bits
Parity
Stop bits
9600
8
none
1
19200
8
none
1
38400
8
none
1
57600
8
none
1
115200
8
none
1
230400
8
none
1
UBX-19014286 - R07
3 Receiver functionality
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