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• Device Instance Upper

Here is how they all relate: the

ECU Instance

and

Function Instance

terminology originates from the SAE J1939 and ISO 11783-5

specification. And they do not exist in the NMEA2000 definition. However, they all do define the same fields in the same CAN-bus
messages which NMEA2000 defines as

Device instance

In more detail: the field that J1939 defines as ECU Instance is in the NMEA2000 specification renamed to

Device Instance lower

The Function Instance is renamed to

Device Instance Upper

. And together they form the

Device Instance

, an NMEA2000

definition.

While using different terms, those fields are the same fields in both standards. Device Instance Lower being 3 bits in length, and
Device Instance Upper 5, together 8 bits. Which is the one byte being the NMEA2000 Device Instance.

The Unique Instance

The

Unique Instance

is one more word used to describe almost the same information. It's used by Maretron, and can be made

visible in their software by enabling the column. The Maretron software itself chooses between Device Instance and Data
Instance.

11.5.5. NMEA2000 Changing Instances

Data instance

Even though we recommend to not change data instances (see explanation and WARNING above), it is possible to change them.

There is no option within Venus OS to change them - a third party tool is required and the only tool that we know can do that is
Actisense NMEA2000 reader.

To change the Data instances, see

this document

Device instance

To change the Device instances, see

this document.

WARNING: these (Victron-)features depend on the Device Instance:

1. For an

ESS system

with Solar chargers connected on a VE.Can network, those Solar chargers must remain to be configured

to their default Device instance (0) for proper operation. This does not apply to VE.Direct-connected Solar Chargers made
available on the CAN-Bus as a Virtual-device, using the NMEA2000-out function. Unless the Device instance of the GX
Device is re-configured to another Device Instance. Which is technically possible but not advised and also never required. But
in that situation the chargers must be configured to the same instance as the GX Device.

2. For systems with managed batteries, the same.
3. For both Solar chargers, as well as AC-Connected battery chargers, when connected in a VE.Can network, they will

synchronise their operation. Charge state and such. For that function to work, all chargers must be configured to the same
device instance.

In summary, for the majority of systems we recommend to leave the Device instance to its default, 0.

11.5.6. PGN 60928 NAME Unique Identity Numbers

The GX device will assign an individual Unique Identity Number to each virtual-device. The number assigned is a function of
the

PGN 60928 NAME Unique Identity Number block

aka

Unique device number for VE.Can

as in above screenshot, as

configured in the settings of the GX Device.

This table shows how changing that setting translates into the virtual-devices as made available on the CAN-bus:

Table 3.

configured Unique Identity block: