Does DCC hardware repeat the most recent packet every 10 ms?

[passenger1955]

I am reading in the DCC documentation that the most recent DCC packet sent out gets repeated every 10 ms. I have a question about this. Is this only true for certain instructional packets? like speedstep and function packets? Or is this true for any packet (regardless)? For example, if the most recent packet was a reset packet, a page preset instruction, a direct write/verify, or a direct CV-bit manipulation - do these kinds of packets get repeated every 10 ms (if they are the most recent command)? Thank you.

[gregc]

considering that a DCC packet is ~5msec long, this could be true if there is only one active locomotiv e (see line 118 of S9.2).  

But this isn't possible if it needs to communicate with many active locomotive ( ten locos would require a minimum of ~50msec to send a packet to each loco).

not sure why you say "most recent DCC packet".   If the most recent is repeated, how can there me anything other than the one packet?

 

[passenger1955]

I read this in 9.2:

"Packets sent to Digital Decoders should be repeated as frequently as possible, as a packet may have been lost due to 115 noise or poor electrical conductivity between wheels and rails."

For some reason I recall reading somewhere that they should be repeated every 10 ms.  So was under the impression that the last packet repeats every 10 ms (until there is a new command). Am I wrong about that?  Does the typical command hardware repeat packets? If so, is this typically every 10 ms? Does it repeat them x number of times? or until the next command?  Are the only packets that get repeated speed and function packets?  Thanks for any answers.

[rrinker]

 10ms is just not doable. Best you can do is send every current packet, then as soon as that is finished, start over again at the head of the packet memory. Your software may want to check for changes and prioritize the changes ahead of unchanged data for the best response, especially for things like hitting the horn button.

 There is a CV in the decoder which controls the packet timeout, but this is Recommended, not Mandatory and not all decoders have it - CV11. When used, this is the amount of time the decoder will maintain current speed without seeing a packet addressed to it.

                   --Randy

 

[gregc]

passenger1955

"Packets sent to Digital Decoders should be repeated as frequently as possible, as a packet may have been lost due to 115 noise or poor electrical conductivity between wheels and rails."

"repeated as frequently as possible"  suggests that it never stops sending commands.   The number of active locos will determine the how frequent the command to a specific loco repeats.  

 

passenger1955

So was under the impression that the last packet repeats every 10 ms (until there is a new command).

A command station doesn't know if a packet is corrupted or if the loco lost power and is reset sitting stopped.

it sounds like you think the command station station only sends new commands  some limited number of times and then goes idle.

[passenger1955]

When you hit the F1 button on your NCE controller, does it send out a single F1  DCC packet? 5 copies of the F1 packet? 10 copies of the F1 packet?

[Bayfield Transfer Railway]

I expect it varies with the manufacturer.

[gregc]

An NCE cab replies to a query from the command station which repeatedly queries or sends commands to each possible cab.

at least one type of response is two bytes: a button code or NoKeyPressed code (0x7d) and a speed byte.    See the NCE Cab Bus Communications Protocol.  So after it sends the latest button press it responds with NoKeyPressed in subsequent queries.

passenger1955

does it send out a single F1  DCC packet?

DCC applies to the signalling on the track to the locomotive.   The signalling between the command station and cabs (controllers) is proprietary.

[DigitalGriffin]

They only send out the speed and direction for the loco in question over again and again.  If you will note sometimes our sound locos stutter and stop for a second causing a reset (dirty track) yet they pickup right where they left off.  That's because the speed and direction is being constantly broadcast.  Yet you might lose something light headlight on/off or bell.

Now as to the implementation of the repeat pattern, that is command station dependent.  The standard doesn't really say it has to be 10 ms later.  Just the next command is 10ms later.  It's equally valid to cycle through all the locos with their commands and then come back and repeat the speed and direction again.