C/MRI - Computer/Model Railroad Interface

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

Summary: C/MRI is an acronym for Computer/Model Railroad Interface. C/MRI is a method of controlling signals and switches. It does not control trains. It can be used with Digital Command Control to implement a prototypical signal system for your layout.


C/MRI was developed by Dr. Bruce Chubb, first appearing in the February 1985 issue of Model Railroader. It was expanded and refined over time, and commercial suppliers for the various components exist. It also appeared in a four part series beginning in January 2004 discussing its application in signalling.

C/MRI consists of a serial interface which allows a computer to connect to the system, which has its own small dedicated computer, and a number of plug in cards. Many people use it for signalling and occupancy detection. You can also interface to it using JMRI. It could be used to implement Progressive Cab Control by using the detection system to activate and deactivate blocks as the train progressed along its route.

C/MRI can provide signalling, computer cab control, computer clock control, lighting control, layout animation, automated display mode operation, and more. Emulating prototypical signalling practice is the core of the system.

The computer can read switch positions, block detection, Central Traffic Control (CTC) and yard panels, key switches, dual control turnouts, directional control, and OS (On Station) sections plus more. Outputs to the railroad allow turnout alignment, signalling from simple to complex, and grade crossing control and animation.

Description from the JMRI Website

C/MRI is a system of digital input and output lines that can be used to connect a computer to a model railroad layout, allowing computer monitoring and control of various things of the layout. The SUSIC (Super Universal Serial Interface Card) is the controller board for a large digital I/O system supporting, via a motherboard, up to 64 digital input and digital output cards, with either 24 or 32 input or output lines per card. The USIC is an older version of the SUSIC. The SMINI (Super Mini-node) card is a stand- alone serial node providing a fixed 24 input lines and 48 output lines. A number of other interface boards are available as part of C/MRI, but they all connect to your computer via an SMINI, a SUSIC, or a USIC. For example, C/MRI's DCCOD occupancy detector board connects to an SMINI (or SUSIC or USIC) input line. Layouts that use C/MRI will commonly have several SMINI's located at different places on the layout, and perhaps one or two SUSIC's located at CTC panels.
C/MRI is not a train control system. You may run C/MRI with DCC (such as Digitrax, Lenz, or NCE systems) or with an analog (DC) train control system. And you can use JMRI with your C/MRI system whether you are using DCC or DC to control your trains. If you are controlling your trains with a system that JMRI supports, you can connect your C/MRI system and your train control system to JMRI simultaneously, each with its own serial input line into your computer. Most C/MRI users who use JMRI run with connections to both their C/MRI and their train control system. There are many advantages to doing so. JMRI allows you to "mix and match" how you control and monitor things on your layout. For example, you can switch your turnouts (track switches) using static decoders on your train control system, and simultaneously use C/MRI inputs to provide turnout feedback to JMRI. JMRI is designed to make both connected systems work smoothly together.

Additional Reading

There are a number of books on the C/MRI system, a list can be found on the Wikipedia page (link below).

For more information: (External Sites)