SAE J1939

2.1 Message Header Description

The figure below illustrates the format of the CAN message ID. A brief description of each field follows.

Priority

This 3-bit field is used to define the priority during arbitration. 0 is the highest priority and is usually associated with high-speed control messages. Low priority is used for non-critical configuration and information messages. The lowest priority value is 7.

Data Page (DP)

This 1-bit field defines on which data page (0 or 1) the message is defined in the J1939 specification. Page 0 contains the messages that are presently defined, while Page 1 is for future expansion according to J1939.

Protocol Data Unit Format (PF)

This 8-bit field determines the format of the message and is one of the fields which determine the Parameter Group Number of the message (see 2.1.6). If the value is between 0 and 239, the message is a PDU 1 format message. These messages are sent to specific addresses. If the value is between 240 and 255, the message is a PDU 2 format message. These messages are not sent to a specific address, but are instead broadcast to the entire network.

Protocol Data Unit Specific (PS)

The PDU Specific (PS) field is the Destination Address (DA) in a PDU 1 Format. In a PDU 2 format the PS becomes the Group Extension (GE). This field is 8 bits long.

Source Address (SA)

This 8-bit field is the source address of the device that sent the message.

Parameter Group Number (PGN)

J1939 defines allowable messages by their Parameter Group Number (PGN). The Parameter Group Number is an 18-bit value that uniquely defines the message purpose. It is composed of the Reserved bit, DP, PF and PS, all of which are described above.

2.2 J1939 Bit Field Location and Byte Ordering

The first data byte is sent first and is referenced as Byte 1. The LSB of the data bytes are on the right and are referenced as Bit 1.

All multibyte data fields are specified in little-endian byte order unless stated otherwise.

The convention used to locate a parameter in the data field is the same as specified in SAE-J1939/71. The format used is "R.x" where R is the byte number and x is the starting bit number within the byte. The length is the number of bits starting at this point.

Example: Location 4.3 with a length of 3 bits would have the value of 1 as illustrated below.

Example: Location 4.3 with a length of 3 bits would have the value of 6 as illustrated below.

2.3 Grayhill Touch Encoder Source Address

The source address of the Grayhill Touch Encoder is set to 242 (0xF2) at the factory. This may be modified dynamically with the proprietary Source Address Command. The source address value is stored in non-volatile memory. Touch Encoder assumes this value at startup but the actual source address is the result of Dynamic Addressing. Multiple Touch Encoder devices can coexist in the same system.

2.4 GUIDE

The following sections describe the different commands and reports that are available for the user interface (GUIDE). Each UI screen of a given GUIDE project has a screen ID associated with it. Each screen contains a set of variables, each with an ID associated with it, that influence the appearance and behavior of UI elements. As presented in the upcoming sections, these IDs are used to identify a particular screen or a variable.

Any variable of any screen can be modified or read using SET or GET commands respectively. Also, by the means of issuing an appropriate SET or GET command, the current screen can be changed or polled. A change of a variable value or current screen, whether resulting from a SET command or user input, triggers a notification message identical to a GET command response as if the corresponding GET command was issued.

Each screen also contains a tree of visual elements that make up the user interface and receive various types of events. Event occurrence at a particular element results in an event notification message. In the same fashion as screens and variables, visual elements are identified by their IDs.

All GUIDE commands use the Proprietary A PGN (0x0EF00). The GUIDE command response messages and notification messages use the Proprietary B PGN 0x0FF11*.

* The PGN can be reassigned using a configuration message.

2.5 Configuration and Control Message

3.1 Knob Event

Data Length – 5 bytes

3.2 Touch Event

Data Length – 8 bytes

3.3 Gesture Event

Data Length – 7 bytes

3.4 Scene Event

Data Length – 7 bytes

4.1 Modify GUIDE Response PGN

By default, GUIDE notifications are sent using the PGN of 0x0FF11. This value may not be desirable as each message will possibly be received and processed by many nodes. Moreover, if a message does not fit a single CAN frame, it will be segmented in accordance with J1939 BAM, incurring significant latency. To combat such inefficiencies, it is possible to assign a different value for the GUIDE notification PGN. For instance, one may choose to specify a PGN that will target only a specific node.

4.2 Modify Message Priority (COMING SOON)

Data Length – 8 bytes

dd – The new priority. Valid Range: 0..7
xx – Don't Care. Should be 0xFF following J1939 convention
0x55 – Low byte of 16 bit key
0xAA – High byte of 16 bit key

Applies to all messages sent by the Touch Encoder.

4.3 Modify Source Address

Data Length – 8 bytes

dd – The new source address. Valid Range: 0..253
xx – Don&##39;t Care. Should be 0xFF following J1939 convention
0x55 – Low byte of 16 bit key
0xAA – High byte of 16 bit key

4.4 Backlight Intensity

Data Length – 8 bytes

dd – Has a value between 0 and 100 and is the percentage of backlight intensity
xx – Don't Care. Should be 0xFF following J1939 convention

4.5 Raw Input Event Report Enable/Disable

Raw Input Event (RIE) reports can be enabled/disabled using this command. In order to use the default RIE Report PGN (0x18FF0E), the user can simply send the 2-byte message shown below. In order to define a new PGN for the RIE Reports, the user should use the longer 5-byte message. For more information on RIE Reports, refer to Raw Input Event Reports.

Data Length – 2 bytes

Data Length – 5 bytes

4.6 Enter Suspend Mode

The device can be instructed to enter a low-power mode by issuing the following single-byte command.

Data Length – 1 byte

Note: Issuing any other host command (e.g. Backlight Intensity), causes the device to wake up from suspend.

4.7 Live Update Request

Data Length – 8 bytes

Example: The following message requests the update of Touch Encoder project. The origin (0x21) obligates itself to upload a file of size equal to 2212495 bytes (roughly 2.11MB) over PGN 0x13300. The file, once successfully submitted, will be used to update the TE project.

To learn more about the live update procedure, see our Live Update guide.

4.8 Configure NAME

Certain fields of the Touch Encoder NAME are configurable. The following command allows to set a single field at a time. The field to be set is identified by Selector. The value is taken directly and applied to the selected field up to the maximum bit length of the field. The changes take effect upon the next power cycle. For more information on the NAME field, refer to SAE-J1939/81.

Service Tool Authentication is required to execute this command.

Data Length - 5 bytes

4.9 Service Tool Authentication Request

This command initiates a service tool authentication session.

Data Length - 5 bytes

To learn more, refer to Service Tool Authentication.

5.1 RIE Report Types

Touch RIE

Note: The Contact X and Y-coordinates are in the screen coordinate space.

Encoder RIE

* Note: The maximum value for the encoder raw value is limited by the number of detents of the encoder hardware. Default encoder value range: 0...31.

6.1 Address Claimed

* Refer to J1939 base document for the Function value based on the Industry Group and Vehicle System combinations

6.2 PGN Request

The following are the supported PGN&##39;s that can be requested from the Touch Encoder. If the request is unsupported, the device responds with a NACK (Refer to J1939-21).

6.3 Acknowledgement Message

*Group Function Value is context-dependent. Typically, if the acknowledgement is sent in response to a Configuration and Control Message, the Group Function Value equals the value of the command field (byte 1).