Press "Enter" to skip to content

jCOM.J1939.GPS – SAE J1939 GPS Module – User Manual

The jCOM.J1939.GPS device connects to an SAE J1939 network and reports the vehicle position (PGN 65267) with a one second frequency, according to the SAE J1939-71 Standard. 

Functionality

The integrated J1939 protocol stack automatically negotiates a node address in the range of 128 to 247. The GPS data is broadcast by using the global destination address (255 = 0xFF). The device’s firmware can be updated on-site per the integrated RS232 port, which also allows the loading of customer-specific features.

Please feel free to contact us, in case you need any additional or modified functionality. We can provide solutions within shortest time, and we don’t charge when the modifications are minor or help to improve our product.

Automatic CAN Baud Rate Detection

The jCOM.J1939.GPS device provides automatic CAN baud rate detection, which requires some special attention when connecting the device to a network. For more information see our post:

In accordance to SAE J1939-16 Autobaud, the device is considered to be classified as Adjustable Baud Rate PI-ECU (PI = Permanently Installed). The device remains in Silent Mode indefinitely until it detects a valid J1939 data frame.

Address Claim & NAME Setting

The NAME used for address claiming does currently not include a manufacturer code. In fact, the device is using a NAME that avoids any interference with the J1939 network, i.e. in case of an address conflict our device will always yield. The jCOM.J1939.GPS will negotiate an address between 128 and 247 with a preferred address of 128.

PGN 65267 – Vehicle Position

The output of the application is PGN 65267 (0xFEF3) according to the SAE J1939-71 standard:

Transmission Rate: 1 second
Data Length: 8 bytes
Default Priority: 6

Start Position Length Parameter Name SPN
1 – 4 4 bytes Latitude 584
5 – 8 4 bytes Longitude 585

SPN 584

Resolution: 10^-7 deg/bit, -210 deg offset
Data Range: -210 to 211.1008122 deg
Operational Range: -210 deg (SOUTH) to 211.1008211 deg (NORTH)

SPN 585

Resolution: 10^-7 deg/bit, -210 deg offset
Data Range: -210 to 211.1008122 deg
Operational Range: -210 deg (WEST) to 211.1008211 deg (EAST)

GPS Data

The image below demonstrates the data output of the GPS module (CAN/J1939 port).

GPS CAN Bus Data

Line 1 documents the address claim. The application is set up for an address range between 128 (0x80) and 247 with a preferred address of 128. The following lines are valid GPS data (pointing to our Windows 10 PC in our office; we moved the board as far as the cable allowed and changes are visible).

Please note that the SAE J1939-71 Standard uses Small Endian for data transmission, meaning LSB comes first, MSB comes last. Also be aware, it might take several minutes after startup before the GPS module can provide a valid position (Once found, it takes only seconds with clear reception). The SAE J1939-71 Standard does not cover such a scenario, i.e. the data output for such a case is not defined. Rather than not sending anything at all, we chose to set all 8 data bytes to 0xFF.

Request Messages

The jCOM.J1939.GPS device reports time & date (PGN 65254) on request. 

As the name implies, a Request Message is being used to request data globally or from a specified destination (i.e. node address).  The Request message  is associated with a specific PGN(PGN 59904) as described below:

J1939 Request message type

The following table demonstrates the use of fields of a Request message type:

Request Message Type - Use of Fields

For more information on the SAE J1939 protocol in general and Request messages in particular, see A Comprehensible Guide to J1939.

PGN 65254 – Time/Date

Transmission Rate: On Request
Data Length: 8 bytes
Default Priority: 6

Start Position Length Parameter Name Remark
1 1 byte Seconds SPN 959 – 0.25 sec per bit
2 1 byte Minutes SPN 960
3 1 byte Hours SPN 961
4 1 byte Month SPN 963
5 1 byte Day SPN 962 – 0.25 days per bit. Example: 1,2,3,4 = Day 1, 5,6,7,8 = Day 2, etc.
6 1 byte Year SPN 964
7 1 byte Local minute offset SPN 1601 – Always set to 0xFF to indicate UTC (GMT)
8 1 byte Local hour offset SPN 1602 – Always set to 0xF9 to indicate UTC (GMT)

Note:The jCOM.J1939.GPS device transmits Greenwich Mean Time (GMT).

Requesting Time/Date

The following image shows a screen shot of our jCOM1939 Monitor software (in combination with our jCOM.J1939 USB hardware) requesting and receiving time & date:

J1939 Request Time And Date

PGN 65256 – Vehicle Speed/Direction

Transmission Rate: 1 second
Data Length: 8 bytes
Default Priority: 6

Start Position Length Parameter Name Remark
1 2 bytes Compass Bearing SPN 165 – 1/128 deg per bit
2 2 bytes Navigation-Based Vehicle Speed SPN 517 – 1/256 km/h per bit
3 2 bytes Pitch SPN 583 – Not used; Always set to 0xFFFF
4 2 bytes Altitude SPN 580- Not used; Always set to 0xFFFF

 

 

 

© 2018 Copperhill Technologies Corporation