Lights operation with 2 decoders (Class 800 or HST)

[Michael Tanguy]

Hello,

Could someone please let me know how to change the default direction for the lights when  programming decoders, one for the driving unit and one for the dummy trailer so that both sets of lights operate correctly. Many Thanks, Michael

[Chrissaf]

When a train is designed from the outset to have a motor car and a dummy car and both cars are DCC ready (have sockets) then they would normally be wired at the factory to do the correct light control automatically.

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If you have been fitting your own decoders (hard wired) into a motor and dummy car that have not been factory fitted with decoder sockets. Then in the dummy car you reverse the white and yellow wires leading from the decoder.

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If your dummy car is DCC ready and has a socket, but when fitted with a decoder the directional lights operate opposite to expectations. Then you could either take the dummy car apart and reverse the white and yellow wires as mentioned above. Or toggle the Bit0 value in CV29 on the decoder that is fitted to the dummy car. You only toggle the CV29 Bit0 value in the dummy car. If you do this in the motor car, then the train will run in the opposite direction. However, some posts on this forum indicate that changing CV29 Bit0 to perform this function is not always successful for some decoders.

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To toggle Bit0 in CV29. You first need to read the value of CV29. If it is an even number, add 1 to it. If it is an odd number subtract 1 from it. Then write back the new number to CV29.

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For example:

if CV29 reads as 6......add 1 = 7 and write 7 to CV29

if CV29 reads as 7......subtract 1 = 6 and write 6 to CV29

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If directional lights don't function at all, make sure that firstly you have sent the F0 command from your controller when the train is on the main track. And secondly, that CV29 Bit1 is set to enable 128 Speed Steps.

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To check 128 Speed Steps enabled / disabled status, read the value of CV29 and put the value in this on-line tool (bottom row in table where it says 'BackCalc'), then click the 'BackCalc' button:

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http://www.2mm.org.uk/articles/cv29%20calculator.htm

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Follow appropriate controller specific guidelines regarding reading and writing CVs to decoders in dummy motor cars. Some controllers & decoders must have a motor attached to the decoder. Thus the dummy car decoder first has to be configured in the motor car, then moved to the dummy car. Some controllers allow the motor car and the dummy car to both sit on the same programming track at the same time (this is only practicable if both decoders are going to have exactly the same settings for every configurable parameter). If the decoders are going to have different configurations as in the case of CV29, then you program the dummy car first, then remove it from the programming track before then programming the motor car with the different settings.

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The easiest foolproof option is to put the dummy car decoder in the motor car first for programming, then physically move it to the dummy car. Then put the motor car decoder in the motor car and then program that as a separate exercise.

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Of course, you can not do any of the CV29 changes documented above if you have the Select controller with less than V1.6 firmware (due Autumn/Winter 2019)

[Michael Tanguy]

Hello Chris,

Many many thanks for your reply and for the detailed information. It is really appreciated.

Well I changed the value of CV29 to 3 on the decoder in the dummy car (Paddington Class 800)

and now the lights work correctly. Very happy I learned something useful today.

Thanks again,

Michael 

[Chrissaf]

Glad to have helped. CV29 value 3 is the absolute basic setting you would need............... 1 for the reverse direction and 2 for the 128 Speed Steps....1 + 2 making CV29 write value 3 in total.