NMRA: Standards

Summary: The best-known activity of the NMRA is the creation of Standards, and documents known as Recommended Practices (RP), for model railroad equipment. Many standards defined by the NMRA are widely followed by the industry and modellers, including their HO scale track and wheel standards (S-3, S-4) and related RPs (RP2, 8, 10-15, and 25), the Digital Command Control (DCC) standard set (S-9.1, S-9.2, and RP9.1.1 through RP9.3.2), and NMRAnet standard set (S-9.7) in development.

The main reason for the creation of the NMRA was to encourage inter-operability between manufacturers, which was a serious issue in the early days. Your trains may or may not have worked on a friend's layout. Today, thanks to the efforts of the NMRA, that is not a problem.

Digital Command Control

• NMRA Standards and Recommended Practices

The NMRA Standards web page is the authority. The Standards, RPs, and TNs listed link to their page, and those links can change without notice.

This is a partial list of Standards related to DCC. For the latest revisions, see the NMRA Website.

Standards

• S-9.1 DCC Electrical Standard - (revised March 7, 2020)
  • S-9.1.1 The NMRA DCC WG is currently working on this Standard. It is anticipated that this standard will address connectors that are currently being used by manufacturers, one sub-standard per connector. For a list of all the connectors, use RP-9.1.1 as the current reference.]

• 9.1.1 Decoder Interfaces (1/31/2021)
  • TI 9.1.1 Sources for Connectors for DCC Decoders - (2/20/2021)
  • S-9.1.1.1 Six and Eight Pin Decoder Interface (11/13/2020)
  • S-9.1.1.2 JST-9 Decoder Interface (11/13/2020)
  • 21MTC Decoder Interface S-9.1.1.3 (11/13/2020)
    • 21MTC Decoder Interface Technical Note TN-9.1.1.3 (12/1/2020)
  • S-9.1.1.4 PluX Decoder Interface (Currently under development)
  • S-9.1.1.5 Next 18 and Next 18S Decoder Interface (12/6/2020)
  • TN-9.1.1.5 Next 18 and Next 18S Decoder Interface (1/6/2021)​

• S-9.1.2 DCC Power Station Interface - (2012)
• S-9.2 DCC Communications Standard - (2004)
  • S-9.2.1 DCC Extended Packet Formats - (2012)
  • S-9.2.2 DCC Configuration Variables - (2012)
  • S-9.2.2, Appendix A, DCC Manufacturer ID codes - (revised Feb 26, 2019)
  • S-9.2.3 DCC Service Mode - (7/2012)
  • S-9.2.4 DCC Fail Safe - (7/2012)
• S-9.3 DCC Bi-Directional Communications Standard
  • S-9.3.1 (discontinued)
  • S-9.3.2 DCC Basic Decoder Transmission - (updated 12/20/2012) UNDER REVISION

Recommended Practices

• RP-2 Track Gauges
• RP-9 Electrical
  • RP-9.1.1 Electircal Interface & Wire Color Code for DCC

Technical Notes

• TI 9.1.1 SOURCES FOR CONNECTORS FOR DCC
• TI 9.2.1 ADDITIONAL COMMUNICATIONS FORMAT FOR DCC (RELEASED FOR COMMENT)
• TI 9.2.3 SERIAL USER STANDARD INTERFACE FOR DCC
• TN 1-05 for RP-9.2.3 SERVICE MODE DECODER LOCK FOR DCC (RELEASED FOR DISCUSSION)
• TN 2-05 Draft for RP-9.2.3 ELECTRICAL SPECIFICATIONS FOR DCC (DRAFT FOR DISCUSSION)
• TN 3-05 for RP-9.2.1 ELECTRICAL SPECIFICATIONS FOR DCC DECODER TRANSMISSION (DRAFT FOR DISCUSSION)
• TN 4-05 for RP-9.2.1 ELECTRICAL SPECIFICATIONS FOR DCC DECODER TRANSMISSION (DRAFT FOR DISCUSSION)
• TR 1-05 SERVICE MODE DECODER LOCK FOR DCC (DRAFT FOR DISCUSSION) - (3/6/2005)

Layout Command Control

• S-9.7.x Layout Command Control (LCC)
  • This page has a number of standards related to LCC.

Standards Under Review

Oct-2020

• https://www.nmra.org/dcc-rps-standards

The following standards are currently under review and released for comments:

1. S-9.1.1.3 21MTC Decoder Interface
   1. TN-9.1.1.3 21MTC Decoder Interface

Standards to be Voted On

1. S-9.1.1 Decoder Interfaces
2. S-9.1.1.1 Six & Eight pin Decoder Interfaces
3. S-9.1.1.2 JST-9 Decoder Interface
4. S-9.1.1.5 Next 18 & Next 18s Decoder Interfaces

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