DCCWiki, a community DCC encyclopedia.
Jump to: navigation, search

Summary: SUSI is an interface between DCC Multifunction Decoders and additional modules.

SUSI - Serial User Standard Interface

Interface definition between decoders and external extension modules (SUSI-modules). Developed by Dietz the SUSI interface allows a multifunction decoder to pass the information on to additional devices – up to three (3) SUSI modules. Function keys on the throttle control the module(s).

SUSI is an NMRA Standard TI-9.2.3. (Also known as the SUSI 1.3 Specification). More details can be found in the standard.


SUSI Applications

At present, there are two core applicatons for SUSI-modules.

Sound Modules
Modules to generate sound based on the messages from the decoder. For example, this allows the sound to change based on speed changes, as the decoder is requested to reduce speed the SUSI sound module could play a brake squeal sound.
Additional functions
Modules to increase the number of outputs available. These are defined as Auxiliary outputs. The specifications allow for Aux. outputs A-P to be defined. These can then be mapped (as with on-decoder functions) to DCC functions e.g., F5 triggers AUX Output D.

Some SUSI modules can control external devices such as a smoke generator. By using the SUSI interface, the smoke unit can respond to outputs from the decoder for more realistic effects.

SUSI can also be used as an interface to a LISSY module, a communications technique similar to RailCom except it uses Infrared Light.

With the arrival of multifunction decoders with integrated sound, the need for SUSI declined. SUSI devices are still available, often used with large-scale decoders. While originally developed for DCC, some Selectrix decoders also have SUSI interfaces.


SUSI and the SUSI-LOGO were developed by

DIETZ MODELLBAHNTECHNIK Hindenburgstraße 31 D-75339 Höfen Germany

e-mail: [email protected]


The hardware connection to the SUSI module is a PTP[1] connection with 2 signals plus 2 supply lines. The data line must be pulled up to 5V. The clock and data lines must have a 470R resistor in series on both sides, µC and Module. Since the connection between the decoder and module is short, no error correction is used.

The clock signal must not have a period greater than 500µs; the high and the low times of that period must be greater than 10µs. Data must be stable at the clock's falling edge. Two or three bytes are transmitted with LSB (Bit 0) first.


SUSI Interface

The connections between the decoder and the SUSI module uses 4 wires:

Pin Number Signal Wire Colour
1 Ground Black
2 Data Grey
3 Clock (CLK) Blue
4 Power Red

Colours are those recommended by the NMRA.

Technical Details from the NMRA Standard

The connection is made by means of a 4-pole socket (JST SM04B-SRSS-TB (side entry) or JST BM04B-SRSS-TB (top entry) on both decoder and SUSI- module. Connection is established by cable with plug (JST 04SR-3S or SHR-04V-S-B) on both sides and pin 1 connected to pin 1, etc. It is allowed to have the wires on the SUSI-module side directly soldered to the PCB.

Other Interfaces

PLuX connectors also support SUSI.


A specific set of CVs has been assigned to SUSI modules to store their settings: 897-1024

As you can connect up to 3 SUSI modules to a host decoder the CVs are split into 3 ranges to prevent conflicts between SUSI modules. These are selected by setting CV 897

Name CV Range CV 897
SUSI-I 900 to 939 1 (or Zero)
SUSI-II 940 to 979 2
SUSI-III 980 to 1019 3

Full details of the CVs can be found in the NMRA SUSI 1.3 Specification

Decoders with SUSI Support

A number of European DCC manufacturers offer compatible decoders and SUSI devices.

Multifunction Decoders

SUSI Modules

Further Reading

  1. Point to Point