J1939 ECUs and Variables

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J1939 ECUs and Variables

This page is a follow-up of the general introduction into J1939 and the general setup required to use J1939.

Here we create J1939 ECUs and their variables.

There is one more page describing setup of J1939 PGN mappings.

hmtoggle_plus1Defining other ECUs on the J1939 Network

The display has to identify every ECU it should communicate with.

•In a static network the source address of each ECU is sufficient for this purpose.

•For networks using dynamic address claim each ECU has to be identified by its J1939 name.

The main purpose of the ECU configuration is to use these ECUs as variable owners.

Note: The display will request an address claim if it finds an unknown source address on the bus. If there should be an ECU that does not answer this request, it should be configured here even if it does not otherwise communicate with the display.

ECUs are configured in the same "Terminal and Owner ECU(s) Configuration" dialog that was used above to activate J1939 protocol and to configure the display's address. ECUs are configured in the lower part of this dialog:

create static J1939 ECU

1.Type a name describing the ECU

2.Press "Add"

Then the new ECU will automatically be selected and one can modify the other parameters:

configure static J1939 ECU

3.Provide a description that could help others to understand better which ECU is meant here.

4.Select "Static" since we want to configure an ECU with a static address here (ECUs with dynamic addresses are handled below).

5.Type the source address this ECU will use. This can be done in decimal or hexadecimal format. Anyways hexadecimal is shown.

6.In case the ECU is not needed anymore it can be deleted again. If it should already own any variable all these will be owned by the display afterwards.

The first steps are the same as for the ECU with static address described above - with the exception of the "Address Claim" field which has to be set to "dynamic" and then the "J1939 ECU Name" field becomes unlocked:

configure dynamic J1939 ECU

 

1.... 3. Are the same steps as above.

2.Select "Dynamic" since we want to configure an ECU with dynamic address claim here

3.The "Source Address" chosen here is not really relevant - the display will identify the ECU by its J1939 name. Anyways it's a good idea to configure the preferred address of the ECU here.

4.Press the ". . ." button in the J1939 ECU Name field in order to configure the ECU's J1939 name. This will open a dialog similar to the one used to configure the display's name earlier:

configure name of dynamic J1939 ECU

 

The fields of the J1939 name are explained here.

One could find out the name of an ECU with a CAN tool the name is the data part of the address claim message looking like this in a CAN tool:

 

    18EAFFFE  3  00 EE 00

    18EEFF4D  8  23 47 E0 FF FF 00 FE FF

 

The first line shows a "request for address claimed" which you could send from your CAN tool to get the response in the second line.

This second PGN 0x00EE00 is the address claim coming from ECU with source address 0x4D and having the name we have as default in the dialog.

The most convenient way to enter this name obtained with a CAN tool is provided in the center of the dialog.

Note: In our CAN example the bytes belonging to the "Identity Number" field are "23 47" whereas the tool default is "00 00" because we expect them to be ignored anyways.

The message above shows the J1939 name of one specific ECU. The challenge now is to decide which parts of the name are relevant for the display to recognize this ECU on the bus.

 

Masks are used to ignore those parts of the J1939 name which change from ECU instance to ECU instance while evaluating the rest. Masks are applied via a bit-wise AND so that a bit set to 0 on the masks means to ignore the respective bit of the name.

 

ECU is recognized as the one configured in the dialog

 

   if ( (ECU_name_on_CAN AND configured_mask) == (configured_ECU_name AND configured_mask) )

 

By default every bit of the configured name is considered - with the exception of the "Identity Number" field which should be derived from the ECU's serial number.

 

Note: It seems the default mask for "Function" is 0x01 and not 0xFF as it should be.
hmtoggle_plus1Adding Variables to the J1939 ECUs

As mentioned above we mainly configured the J1939 ECUs because they own some variables whose values we want to show and/or modify on display.

Before we can use these variables we have to do two things:

1.Create the variables and use one of the J1939 ECUs as owner.

2.Define the PGNs we want to use to send and receive the variables.

Knowing that we could end up with a lot of variables per ECU it's a good idea to create one variable group per ECU. Of course you are free to organize variables in groups however you prefer.

create J1939 variable group           add J1939 variable group

1.Open Menu "Communication"

2.Select "Variable Group Configuration ..."

3.In the dialog that opens press "Add Group" to create a new variable group

4.Type a sensible name for the new group

new J1939 variable group

 

5.Once you pressed "Enter" to confirm the new group name it will move according to alphabetical order of all groups.

6.Press "close" once you're finished creating or deleting variable groups.

If you delete a variable group that is not empty, all the remaining variables of the deleted group will be moved to group "Common" which is the default for all user defined variables.

Creation of J1939 variables is similar to all other variables:

add J1939 variable menu                   add J1939 variable dialog

 

1.Open the "Communication" menu

2.Choose "Variable Manager ..." entry

3.Variable Manager dialog opens (which can be used as shortcut to all variable related tasks)

4.Press "Create a new Variable ..." button

5."Add new variable" dialog opens

6.Fill in a name of the variable

7.Type an index for the variable. You are free to enter the value in decimal or hexadecimal, starting with "0x". Anyways hexadecimal will be displayed. (Although the concept comes from CANopen you should use index and subindex as a means of ordering and grouping of variables)

8.Add a subindex for the new variable. Note: Combination of index and subindex has to be unique among all variables in the GUI definition.

9.Select signed or unsigned data type at least as wide as the variable will be in CAN message.

10.Change owner from default "PClient" to the newly created J1939 ECU. Note: If you keep "PClient" you could handle the variable also but would not notice if the ECU is not available anymore.

11.Select the newly created variable group for the variable.

12.Press "Add" to finally create the new variable with the settings made above.

Once you did all that the dialog could look like this:

Filled J1939 add variable dialog

Now you can either create more variables by editing the settings with or without "Reset" or leave the dialog with "Close".

After closing the "Add New Variable" dialog you can modify all the properties of the variable(s) just created or already existing in "Variable Manager" dialog:

variable managershowing new J1939 variable

As you may have noticed the "Description" was added and the variable type was modified from "INTEGER8" to "UNSIGNED8".

For a detailed description of all the variable properties and events please refer to variables menu description.

 

There is a second option to create variables:

create variable in variable view

 

1.In variable view press the "Var +" button

2.A new variable with default settings appears

3.You can double click each property and edit it.

Warning: If you type a group name not defined yet, a new variable group will be created.

Warning: Depending on your sorting option the variable can "disappear" whenever a modification is confirmed.

More details on this option can be found in variable view.

 

So the recommendation is to create variables following the first option and use the variable view to manage and modify existing variables.