Cerbo GX Installation

• 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: 1 2 3 4
GX device 500 1000 1500 2000
1st virtual-device (for example a BMV) 501 1001 1501 2001
2nd virtual-device (for example another BMV) 502 1002 1502 2002
3rd virtual-device (for example a third BMV) 503 1003 1503 2003
Cerbo GX Manual
Page 60 Marine MFD integration by NMEA2000