General Protocol Information
XpressNet, and the predecessor versions of the X-bus protocol, are based on the RS485 multidrop half duplex serial communications bus. It consists of a start bit, (0), nine data bits, 1 stop bit (1) and no parity, at 62.5 kilobits/sec. The protocol information is freely available from the Lenz Website.
XpressNet supports a maximum of 30 devices (addresses 1 tp 31). Each is provided with a window for transmission at regular intervals. Certain situations will override that requirement.
XpressNet uses a four wire connection, via a DIN plug or a 6 pin RJ connector.
- L = Positive supply voltage for the devices on the network, 12VDC
- M = Supply ground
- A = Receive (RX) / Transmit (TX) non-inverting RS-485
- B = RX/TX Inverted RS-485
If you accidentally reverse the A and B connections, data will not be transmitted.
- The LI100 interface allows connection of an RS-232 serial device and the RS-485 based XpressNet.
For more details, see XpressNet Specification document from Lenz.
The RS-485 serial protocol has a limit of 100 metres, XpressNet is capable of up to 1000m due to the low data rate of 62.5 kiloBits. A loop should be avoided for best operational conditions.
In addition to Lenz, several other manufacturers have implemented the X-bus V3 protocol:
- Atlas For the Commander and HandCommand
- Roco For the LokMaus II, LokMaus III and MultiMaus. Roco calls its implementation RocoNet.
- ZTC For their DCC systems and throttles
- CVP For a wireless throttle base station
- ESU For a wireless throttle base station
- Hornby For their Select and Elite DCC systems
Arnold also used the XBUS protocol for the Arnold Digital system. Arnold Digital equipment should be compatible with versions up to Xpressnet version 2.3, but the system is no longer a supported product. Arnold is now part of Hornby International.
Different manufacturers have chosen to use different connectors for wiring their XPressNet throttle networks. The most commonly used connectors are RJ12 modular plugs and 5 pin DIN plugs. ZTC Controls uses an 8 pin mini-DIN connector.
DIN Plugs were often found on European audio equipment, as well as computer keyboard connectors, because they were rugged and easy to use. Registered Jack/RJ connectors are often found on telecommunications equipment.
The terminal block plug connectors on the back of Lenz Command stations are made by (compatible with?) Phoenix and are available as spares from Lenz, Radio Spares (United Kingdom, but ship worldwide) and Mouser (USA)
Thanks to the Gavin Liddiard and Paul Bender on Digital Plus by Lenz Yahoo group for terminal block info.
Additional Information about XpressNet
The RS-485 standard was chosen as it is robust and parts cost is decreasing. Other DCC manufactures such as NCE, Wangrow, RamFixx and ZTC have also chosen RS-485 for their throttle networks.
XpressNet uses polling to find devices on the bus. This only takes a few seconds. After all the devices have been identified the system functions seamlessly, only requiring a few milliseconds very few seconds to poll the network.
The XpressNet throttle network uses 2 pairs of wires, one is for serial data (RS-485), the other provide power to devices on the network.
Number of Throttles
Up to 30, but this can be increased with better serial drivers. The original RS-485 specification allows for 32 devices.
The throttles themselves are intelligent, and together with the Command Station create the DCC System. Upgraded throttles allow for more functions and other features without the requirement of a new command station.
The original software in the command stations had some issues which gave the impression that the network was overloaded. A software update corrected that issue.
Software updates can also add features and give improved operations to the system. If you have an old command station, check which version of software is installed and investigate the upgrade possibilities. This is also true of throttles.