Summary: Dynamic Configuration Variables are optional features used for various purposes, such as fuel or water available. They are defined as the range of CVs from 880-895. They are dynamic and used for Unsolicited Decoder Initiated Transmissions.
These Configuration Variables are subject to change.'
Dynamic Configuration Variables 880-895
CVs 880-891 are currently reserved by the NMRA for future usage. Currently there seems to be little usage of these CVs.
Decoder Load, CV 892
This specifies the current load on the decoder as a 7-bit number. Bits 0-6 indicate the load, zero being no load. Bit 7 indicates a positive or negative load.
This CV is volatile and is lost during a power interruption.
Flags, CV 893
Up to 8 dynamic flags can be stored. Bits 0 to 7 are reserved for future use.
Fuel/Coal, CV 894
A value stored here indicates the level of fuel, such as oil or coal, onboard. The locomotive will stop when it reaches zero. A value of 254 means a full load of fuel. If the value is 255, it means this feature is not supported and the contents of the CV are not to be transmitted.
Water, CV 895
Same idea as the Fuel variable, it indicates the amount of water onboard. When the water is consumed (0), the locomotive should stop, as it would in real life. Many accidents occurred when the water level in the boiler decreased to a dangerous level, usually resulting in the failure of the crown sheet and an explosion.
Configuration Variables 896-1024 SUSI (Serial User Standard Interface).