Victron energy Color Control GX Manual page 54

Last update: 2020-08-19 12:10
7.4.3 Classes and functions
As per NMEA2000 specification, these define the types of senders and devices connected to the CAN-
bus. Classes are the main categories, and functions specify it to a further detail.
7.4.4 Instances
NMEA2000 defines three different instances:
1. Data instance
2. Device instance
3. System instance
For all Battery monitors and other devices that the GX Device makes available on the CAN-bus, each
of above types of instance is available, and can be individually configured. Per virtual-device, there is
one Device instance and one System instance. And depending on the type of the virtual-device, there
are one or multiple Data instances. For example, for a BMV-712 there are two data instances, one "DC
Instance" for the main battery, and another one for the Starter battery voltage.
How to configure the instances depends on the equipment and software that is used to read them
from the CAN-bus. Examples of equipment and software meant here are MFDs such as from Garmin,
Raymarine or Navico; as well as more software oriented solutions from for example Actisense and
Maretron. Most, or hopefully all, of those solutions identify parameters and products by requiring
unique Device instances, or using the PGN 60928 NAME Unique Identity Numbers. They do not rely on
the data instances to be globally unique.
The NMEA2000 specification specifies the following: "Data instances shall be unique in the same PGNs
transmitted by a device. Data instances shall not be globally unique on the network. Field
programmability shall be implemented through the use of PGN 126208, Write Fields Group Function.".
In other words, data instances need to be unique only within a single device. There is no requirement
for them to be globally unique – the only exception is "Engine Instance" that at least for now, to cope
with legacy devices, needs to be globally unique (e.g. Port = 0, Starboard = 1). For example, some of
our BMV Battery monitors can measure two voltages, one for the main battery, and one for the starter
battery, and thats where data instancing is used. Similar for multiple-output battery chargers. Note
that there is no need for the installer to change those data instances, as those products are pre-
configured to transmit the relevant PGNs with unique data instances (Battery instance & DC Detailed
instance, in this case).
WARNING: whilst it is possible to change the data instances, changing them on a Victron devices will
render that device impossible to read correctly by other Victron devices.
A note about the Device instances: it is not necessary to assign a unique device instance to each
device on the CAN-bus. Its no problem for a battery monitor and a solar charger to both be configured
with (their default) Device instance 0. Also when having multiple battery monitors or solar chargers, it
is not always necessary to assign each of them a unique device instance. If at all necessary, they only
need to be unique between the devices that use the same Function.
And note that changing the Device instance on a Victron device can change its operation, see below.
System instances
https://www.victronenergy.com/live/
ccgx:start https://www.victronenergy.com/live/ccgx:start?rev=1597831811
Printed on 2020-11-10 02:37