Consisting

Yes, MUing more that two locomtoives is possible. Like anything in DCC, it just requires a bit of reading, some knowledge about MUing locomotives, a wee bit of luck and some forethought.

 I imagine, though, it can depend on what system you're using, thought to the best of my knowledge, they're all (save for, perhaps, Bachmann's System) able to MU more than 2 units together.

AR 

There are actually 3 ways to consist locomotives....

The oldest method, which is sometimes refered to as "basic" consisting, is simply giving the locomtoives all the same address. There is a drawback to this of course... you have no control of functions on individual locomotives...

The next method relies on a function of the command station. I like to refer to this as "Command Station Assisted Consisting (CSAC), but each manufacturer that supports this has their own name for it. The way this works is that the command station keeps track of which decoders are in the consist, and sends a speed and direction command to each of those locomotives seperately. With a CSAC, you can control the functions on each locomotive independenly. Unfortunatly, in order to make this work there is a lot of additional traffic on the DCC track bus. On really busy systems (i.e. systems where there are lots of locomotives running on the layout) you can sometimes see the locomotives fight each other as each one receives a command to change it's speed earlier than it's neighbor.

The final method, which is sometimes refered to as Advanced Consisting (though I personally prefer the term "Decoder Assisted Consisting" (or DAC)), uses CV19 which has been set asside by the NMRA to hold a consist address (which can be any short address allowed by the DCC system). When you're using a DAC, the decoder only responds to speed and direction commands sent to the consist address. This lets the command station send out 1 command for all the locomotives instead of one command for each locomotive. In a DAC, functions are controlled by sending commands to the individual locomotives through thier normal address or, optionally, to the consist address. Whether or not a decoder will respond to a function command sent to it's consist address depends on how CVs 21 and 22 are configured. Some DCC systems allow a DAC to be controlled only by the consist address. Other systems keep all track of what locomotives are in the DAC, and allow you to control the consist from any of those addresses.

At least if you create the consists manually, i.e. on the programming track or on using operations mode programming, both a Basic consist and a DAC can have as many locomotives in them as you want to put into the consist.

With a CSAC, the number of locomotives in a consist is system dependent. There are also system dependent restrictions as to what you can put into a CSAC (e.g., some systems allow address 0 to be in the consist; some systems allow consists to contain other consists).

Paul

This depends on what direction you want the locomotive to travel.

If you want the second locomotive to travel the SAME direction as the first locomtoive, you put the same value in CV19, so both locomotives would have CV19 set to 10.

If you want the second locomotive to travel in the reverse direction, the standards say you add 128 to the consist address, so in this case, you would write 128+10=138 to CV19, and the second locomotive would move in reverse when the first locomtoive is moving forward.

(For the technically inclined, adding 128 to the consist address sets the most significant bit (bit 8) in the CV to 1. This is marked in the NMRA standards as a direction flag, and the other 7 bits in the CV can then be used for a 7 bit "short" address).

Your DCC system may provide other methods for setting these CVs which hides that the addition is taking place when you reverse the locomotive direction.

I hope this helps,

Paul