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DT
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Hornby say on their website:

# External boosters can be supported through the XpressNet port. A standard RJ12 six-way cable can be used to connect the Select to a booster which has an RJ12 socket).

# Up to 9 "Select" units can be connected together for individual control of 9 locomotives providing power is available.

This has got me thinking. As far as I'm aware boosters are not connected together or to the command station using the XpressNet BUS, but rather a separate booster BUS. Right? What boosters connect using XpressNet?

If you can connect 9 Selects together, is there a master command station and do the others act as slaves? Or do they all work as peers? Would this not create conflicts if the various controllers tried accessing the same loco?
 

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QUOTE (Doug @ 8 Dec 2006, 11:56) <{POST_SNAPBACK}>Hornby say on their website:

# External boosters can be supported through the XpressNet port. A standard RJ12 six-way cable can be used to connect the Select to a booster which has an RJ12 socket).
According the the Lenz XpressNet Specification document (6/2003) the only connections defined for XpressNet comms themselves are +12V, 0V, and RS485 bus A & B lines, so four in total. The spec includes a mention of a 6 pin RJ12 connector, but the remaining two connections on it are only described as 'C & D' Control Bus connections, and are only valid on Port A (not Port
. Seems rather strange use such direct references to their own kit's numbering scheme when it is meant to be a general specification for all to use.
It may be that 'C & D' are intended to be used as a low power (logic level) version of the track waveform for distribution to boosters. This is implied in Para 2.1.7, but is not defined any further.
If your kit only has the original DIN plug 'X-Bus' connectors, there are no C & D connections at all.

QUOTE # Up to 9 "Select" units can be connected together for individual control of 9 locomotives providing power is available.
This has got me thinking. As far as I'm aware boosters are not connected together or to the command station using the XpressNet BUS, but rather a separate booster BUS. Right? What boosters connect using XpressNet?
As stated above, it seems to be the case that two spare connections on Lenz's XpressNet Port A are used for this purpose, but they do not really form part of the XpressNet bus itself. If you plug a booster in, it uses just these two connections, if you plug another XpressNet device in, it uses the four 'proper' bus connections, not the 'spares'. This way you can treat the wiring as a daisy-chained bus, whereas it is really two separate set of connections on the same multicore cable.

QUOTE If you can connect 9 Selects together, is there a master command station and do the others act as slaves? Or do they all work as peers? Would this not create conflicts if the various controllers tried accessing the same loco?
How you set the RS485 address of each Select unit is hopefully defined in the Select documentation (not seen it yet). Each one must be set to a different number to avoid conflicts on the bus. Presumably one address is defined as the master (probably address 0). With RS485 systems they are usually arranged as polled Master/Slave(s), not peer-to-peer. It would not trouble the loco itself, only the communications between the Select units on the bus.
 

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QUOTE (Gordon H @ 8 Dec 2006, 12:54) <{POST_SNAPBACK}>It may be that 'C & D' are intended to be used as a low power (logic level) version of the track waveform for distribution to boosters.
Exactly right. A set 100 also has an 'E' connection that provides feedback of overload (short circuit) conditions, but the E connection is optional.
 

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DT
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QUOTE (Mark Thornton @ 8 Dec 2006, 14:58) <{POST_SNAPBACK}>Exactly right. A set 100 also has an 'E' connection that provides feedback of overload (short circuit) conditions, but the E connection is optional.
Yes, the 'E' is optional and shuts down the whole system if one of the remote boosters shorts. This defeats the point of having separate boosters somewhat, but it can be used in the case of a dire emergency.

Regarding the RS485 XperessNet BUS, what other DCC systems connect boosters using this method?

I was looking for the Select manual - found it here.

The manual says (page 18):
There are several "Boosters" on the market, with each one supplied complete with the relevant fitting
instructions.

Consult your Hornby DCC dealer for further details and advice.
The manual goes on to say (page 20), how to configure other units (Walkabout units) that are unpowered, but are connected using the XpressNet BUS. It seems that the powered unit does act as a master controller
 
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