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Looking at the new Hornby Digital range of products we see that they use XPRESSNET as a means of interconnection.
This allows us to add supplementary cab control units around our layout. Or, using XPRESSNET, we can use DCC components from other manufacturers that support the standard (see Compatibility bellow).
XPRESSNET is a high-speed multi-point to multi-point digital network based upon the industry standard RS-485 protocol. DCC systems use XPRESSNET to communicate between its high-speed components such as the command station, hand-helds, tower cabs and its computer interface. XPRESSNET communicates at 62.5 thousand bits per second. It is the highest performance network in widespread DCC use and all its protocols are freely available to both the industry and the hobbyist.
XPRESSNET uses 4 Wires - Two wires are for RS-485 and 2 wires are for 12 volt power and ground. These additional wires provide power to the hand-helds when they are plugged in. Providing power lines with XPRESSNET eliminates the need for batteries in our hand-helds or supplementary transformers for remote cabs
What is RS-485?
An Electronics Industry Alliance (EIA) standard for multipoint communications. It supports several types of connectors, including DB-9, DB-37 and RJ-12. RS-485 is similar to RS-422 but can support more nodes per line because it uses lower-impedance drivers and receivers. Line drivers and receivers are commonly used to exchange data between two or more points (nodes) on a network.
RS485 meets the requirements for a truly multi-point communications network, and the standard specifies up to 32 drivers and 32 receivers on a single (2-wire) bus. With the introduction of "automatic" repeaters and high-impedance drivers / receivers this "limitation" can be extended to hundreds (or even thousands) of nodes on a network. RS485 extends the common mode range for both drivers and receivers in the "tri-state" mode and with power off. Also, RS485 drivers are able to withstand "data collisions" (bus contention) problems and bus fault conditions.
We talk of 2 wires, but XPRESSNET uses 4 Wires. And actually the RJ-12 connectors usually house 6 wires.
What is RJ-12?
RJ-12 jacks and sockets are commonly used in telco installations for phones, modems and security installations. The RJ-12 has a 6-pin connector. Don't confuse it with a computer network connector - the RJ-45 that has a 8-pin connector. The RJ-12 jack will fit into a RJ-45 socket, but the RJ-45 jack will not fit into a RJ-12 socket.
The wires for the 6-pin connector are specified as follows:
And this is how they look on the RJ-12 connector jack:
Connecting an XPRESSNET RJ-12socket to a DIN plug (Lenz) is done as follows:
Compatibility
XPRESSNET / X-Bus which is used by Lenz, Arnold / Lima, ZTC and now Hornby allows these units to be interconnected. Generally it is not advisable to connect a master unit from one manufacturer to a master unit from another, but one can use (for example) Lenz hand cab controllers with the Hornby Elite master unit. In this way, if you are used to one type of controller: Lenz, Roco or ZTC, you can still use the new Hornby system. You should be able to use the Hornby Digital Select unit with a Lenz, ZTC or Arnold master unit. We'll be testing this interconnectivity out as soon as possible.
This allows us to add supplementary cab control units around our layout. Or, using XPRESSNET, we can use DCC components from other manufacturers that support the standard (see Compatibility bellow).
XPRESSNET is a high-speed multi-point to multi-point digital network based upon the industry standard RS-485 protocol. DCC systems use XPRESSNET to communicate between its high-speed components such as the command station, hand-helds, tower cabs and its computer interface. XPRESSNET communicates at 62.5 thousand bits per second. It is the highest performance network in widespread DCC use and all its protocols are freely available to both the industry and the hobbyist.
XPRESSNET uses 4 Wires - Two wires are for RS-485 and 2 wires are for 12 volt power and ground. These additional wires provide power to the hand-helds when they are plugged in. Providing power lines with XPRESSNET eliminates the need for batteries in our hand-helds or supplementary transformers for remote cabs
What is RS-485?
An Electronics Industry Alliance (EIA) standard for multipoint communications. It supports several types of connectors, including DB-9, DB-37 and RJ-12. RS-485 is similar to RS-422 but can support more nodes per line because it uses lower-impedance drivers and receivers. Line drivers and receivers are commonly used to exchange data between two or more points (nodes) on a network.
RS485 meets the requirements for a truly multi-point communications network, and the standard specifies up to 32 drivers and 32 receivers on a single (2-wire) bus. With the introduction of "automatic" repeaters and high-impedance drivers / receivers this "limitation" can be extended to hundreds (or even thousands) of nodes on a network. RS485 extends the common mode range for both drivers and receivers in the "tri-state" mode and with power off. Also, RS485 drivers are able to withstand "data collisions" (bus contention) problems and bus fault conditions.
We talk of 2 wires, but XPRESSNET uses 4 Wires. And actually the RJ-12 connectors usually house 6 wires.
What is RJ-12?
RJ-12 jacks and sockets are commonly used in telco installations for phones, modems and security installations. The RJ-12 has a 6-pin connector. Don't confuse it with a computer network connector - the RJ-45 that has a 8-pin connector. The RJ-12 jack will fit into a RJ-45 socket, but the RJ-45 jack will not fit into a RJ-12 socket.

The wires for the 6-pin connector are specified as follows:

And this is how they look on the RJ-12 connector jack:

Connecting an XPRESSNET RJ-12socket to a DIN plug (Lenz) is done as follows:

Compatibility
XPRESSNET / X-Bus which is used by Lenz, Arnold / Lima, ZTC and now Hornby allows these units to be interconnected. Generally it is not advisable to connect a master unit from one manufacturer to a master unit from another, but one can use (for example) Lenz hand cab controllers with the Hornby Elite master unit. In this way, if you are used to one type of controller: Lenz, Roco or ZTC, you can still use the new Hornby system. You should be able to use the Hornby Digital Select unit with a Lenz, ZTC or Arnold master unit. We'll be testing this interconnectivity out as soon as possible.