DCC address theory

Roland Hooper

Roland Hooper

Registered
Can someone help me with a bit of theory how is it that you can have a loco on addresses 1 and a point on address 1 are they not effectively on the same address. I realise to operate the point in the case of the LGB universal that you have to press Function 1 to tell the MTS you want a point to operate but what does pressing F1 actually do and equally F2 for the loco do in the binary code.
Roland
 
Well a loco address and an accessory address are totally different addresses.

When the central station issues a command to an accessory decoder, it is sending a different request than would be used to control movement of a locomotive. Each device (loco decoder & accessory decoder) is looking for a specific type of request (or requests) from the central station and will normally only act upon it if that request contains the address assigned to that decoder.

Central stations constantly send loco speed and direction information to all active locomotives being run. This reminds the locomotive what it should be doing all of the time. Thus you can set the loco going, physically remove it from the track, wait a while and put it back on again and it will continue on its merry way as it was before.

The central station will also intersperse the loco commands with accessory commands as and when needed.

So when you change the speed of the locomotive on your throttle you are telling the central station to adjust the information being sent to the locomotive. When you use your handset to operate a point you are telling the central station to issue the accessory command.

Hope that helps.
 
Well explained Mark.

Roland, if you *really* want to get down to the bits and bytes of the DCC protocol and differences between controlling multi-function decoders(eg. loco decoders) and accessory decoders then take a look here:
http://www.nmra.org/sites/default/files/s-9.2.1_2012_07.pdf

It also reveals why people sometimes see things such as the "flashing lights" phenomenon when a loco is set to speed 14 steps and the command station is sending 28 step commands.
 
Many thanks to both of you Mark and Nick I have just printed out the NMRA standards did have a look at another one of them documents but it did not cover the decoders in great detail. The reason I am asking is I have the LGB universal decoder and when i go to operate a switch with or without the 55025 connected and do function 1 and address 1 or in deed any number below 12 the train that is running stops. I have returned the universal and MTS for checking out and am waiting a reply. It seems to me that the command is getting corrupted either when sending or receiving and it somehow or another left my loco in NMRA digital standard so when I put it back on the track nothing happened. Then I altered CV29 to analogue and digital and hey ho all worked.
Many thanks
Roland
 
Hi Just re reading what I put and when I put the loco back on the track this was after returning the digital equipment so i therefore was using an analogue controller and it would not move until I set CV29 to analogue and digital.
 
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