Linx Technologies RXM-GPS-R4 - Manual (Page 11)

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VTG – Course Over Ground and Ground Speed
Figure 15 contains the values for the following example:
$GPVTG,79.65,T,,M,2.69,N,5.0,K,A*38
Course Over Ground and Ground Speed Example
Name Example Units Description
Message ID $GPVTG VTG protocol header
Course over ground 79.65 degrees Measured heading
Reference T TRUE
Course over ground degrees Measured heading (N/A, null field)
Reference M Magnetic
Speed over ground 2.69 knots Measured speed
Units N Knots
Speed over ground 5.0 km/hr Measured speed
Units K Kilometer per hour
Mode A
A=autonomous, D=DGPS, N= Data
not valid
Checksum *38
<CR> <LF> End of message termination
Figure 15: Course Over Ground and Ground Speed Example
NMEA Input Messages
The following outlines the serial commands input into the module for
configuration. By default, the commands are input at 9,600bps, 8 data bits,
1 start bit, 2 stop bits, and no parity.
All fields in all proprietary NMEA messages are required; none are optional.
All NMEA messages are comma delimited. Figure 17 outlines the message
identifiers supported by the module.
Serial Data Structure
Name Example Description
Start Sequence $PSRF
Message ID <MID>
Message Identifier consisting of three numeric
characters. Input messages begin at MID 100.
Payload DATA Message specific data.
Checksum CKSUM
CKSUM is a two-hex character checksum as
defined in the NMEA specification, NMEA-0183
Standard for Interfacing Marine Electronic Devices.
Checksums are required on all input messages.
End Sequence <CR> <LF>
Each message must be terminated using Carriage
Return (CR) Line Feed (LF) (\r\n, 0x0D0A) to cause
the receiver to process the input message. They
are not printable ASCII characters, so are omitted
from the examples.
Figure 16: Serial Data Structure
Message ID Values
Name MID Description
SetSerialPort 100 Set PORT A parameters and protocol
NavigationInitialization 101 Reset the modules
Query/Rate Control 103
Query standard NMEA message and/or set
output rate
LLANavigationInitialization 104 Reset the modules
Development Data On/Off 105 Development Data messages On/Off
System Turn Off 117
Performs an orderly shut down of the module
and switches into hibernation mode
Figure 17: Message ID Values