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NMRA Standard CV Definitions for Mobile Decoders

This Document forms part of the “DCC for the Engineer” series, and lists the complete NMRA Standard Configuration Values (ref: S-9.2.2)

You can reference the “DCC Decoder Data” Article for general information.

 

Multi-function Decoder Configuration Variables
CV Name
CV #
Required
Default Value
Read Only
Uniform Spec
Dynamic (Volatile)
Comments
Multi-function Decoders:
Primary Address
1
M
3
Y
Vstart
2
R
Acceleration Rate
3
R
Deceleration Rate
4
R
Vhigh
5
O
Vmid
6
O
Manufacturer Version No.
7
M
Y
Manufacturer defined version info
Manufacturer ID
8
M
Y
Y
Values assigned by NMRA
Total PWM Period
9
O
EMF Feedback Cutout
10
O
Packet Time-Out Value
11
R
Power Source Conversion
12
O
Y
Values assigned by NMRA
Alternate Mode Function Status F1-F8
13
O
Y
Alternate Mode Function Status FL, F9-F12
14
O
Y
Decoder Lock
15 – 16
O
Y
Extended Address
17 + 18
O
Y
Consist Address
19
O
Y
20
Y
Reserved by NMRA for future use
Consist Addr Active for F1-F8
21
O
Y
Consist Addr Active for FL-F9-F12
22
O
Y
Acceleration Adjustment
23
O
Y
Deceleration Adjustment
24
O
Speed Table/Mid-range Cab Speed Step
25
O
Y
26
O
Reserved by NMRA for future use
Decoder Automatic Stopping Configuration
27
O
Y
Under re-evaluation – see details
Bi-Directional Communication Configuration
28
O
Y
Under re-evaluation – see details
Configuration Data #1
29
M
Y
SEE NOTE 1
Error Information
30
O
Y
Index High Byte
31
O
Y
Primary index for CV257-51200000000 – 00001111 reserved by NMRA for future use.
Index Low Byte
32
O
Y
Secondary index for CV257-512
Output Loc. FL(f), FL(r), F1-F12
33-46
Manufacturer Unique
47-64
O
Reserved for manufacturer use
Kick Start
65
O
Forward Trim
66
O
Speed Table
67-94
O
Reverse Trim
95
O
96-104
Reserved by NMRA for future use
User Identifier #1
105
O
Reserved for customer use
User Identifier #2
106
O
Reserved for customer use
107-111
Reserved by NMRA for future use, CV107,108: expanded Mfg. ID,CV109-111: expanded CV7
Manufacturer Unique
112-256
Reserved for manufacturer use
Indexed area
257-512
Indexed area – see CV# 31,32, Index values of 0-4095 reserved by NMRA
513-879
Reserved by NMRA for future use
880-891
Y
Reserved by NMRA for future use
Decoder Load
892
O
Y
Y
Dynamic Flags
893
O
Y
Y
Fuel/Coal
894
O
Y
Y
Water
895
O
Y
Y
SUSI Sound and Function Modules
896-1024
O
Y
See TN-9.2.3

 

Notes:

  • If any of these features are provided, then this CV is Mandatory
  • Not All Digital Decoders don’t implement all the CVs, but if the function is provided the relevant CV information must be adhered to.

 

Definitions

  • Mandatory (M)
    CVs identified at Mandatory must be present to conform to the standard

 

  • Recommended (R)
    Those marked Recommended the NMRA strongly encourages their implementation

 

  • Optional (O)
    Optional CVs can be included if the manufacturer wishes.

 

  • Read Only
    Indicates a CV that is set and cannot be altered.

 

  • Uniform Specification
    CVs are specific to the implementation and no uniform specification is needed. Others must be implemented in a uniform manner to maintain compatibility. If marked Yes, the CV must be implemented according to a common specification. If there is no Y in the column, the CV must be used for its designated purpose, but the actions taken by the decoder for a certain CV value can vary among decoder makers.

 

  • Dynamic
    These CVs are used for Unsolicited Decoder Initiated Transmission.