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Speed steps
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| This article is apart of decoder features topics. |
| Decoder Features |
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Movement & speed Programming Lighting & Effects |
| DCC Core components |
| Track work components |
Speed steps can be though of has how many speeds there are between stopped and full speed. That is, as you turn the knob on your DCC throttle, how many speeds can you achieve. For example, if you had 4 speed steps (stopped, slow, medium, and full), you wouldn't have much fine control. In our example, you would turn the knob and the train would lurch to it slow speed. The next step up, and it lurches again to it's medium speed, and then again to full speed. This isn't very realistic, and doesn't allow for very much control.
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[edit] Choices
With DCC, there are three speed step choices: 14, 28, and 128. Lenz also had 27 and 55 speed steps that were a simulation of some kind - it isn't covered in the NMRA standards and RPs. It's unclear if they still offer these odd speed steps now that they do 128 speed steps.
[edit] 128 Speed steps
There is an optional NMRA 128 speed step mode available from both decoders and command stations that support it. Both the decoder and the command station controlling it must support this feature at the same time for it to work. A decoder switches to 128 speed step mode automatically at the track level when a it receives a 128 speed step command from the command station. The decoder likewise will switch back to 14 or 28 speed step mode automatically when it receives a command in that speed command format. Unlkike 14 and 28 speed step commands, the decoder does not need to pre-programmed to enable 128 speed step mode operation. It is always on ready to be used at any time if it supports it.
[edit] 128 Steps is really 126 Steps
The term "128 speed steps" is a bit of a misnomer. It should be called 126 speed step mode for consistency, much like the 14 and 28 speed steps are accurately called.
You would normally expect the maximum to be 127 since that is the largest value that can be encoded in the 7 bit binary field transmitted in a 128 step speed control packet. The lowest speed step (step 0) is stop. The missing speed step (step 1) means emergency stop (ie stop NOW and ignore deceleration settings). So, your command station's speed steps 1 to 126 actually correspond to 2 to 127 as encoded in the DCC packet.
[edit] Which Systems?
Some command control systems (previous to DCC) advertised forward and reverse speed steps combined - 128 speed steps would be 64 forward and 64 backward. But with DCC, when you're using the 128 speed step mode, you have 128 speed steps forward and 128 speed steps in reverse (for a total of 257 speeds - 256 moving speeds, and one stopped). 14 and 28 speed step modes work the same way.
Almost all systems now support 14, 28, and 128 speed steps - simultaneously. But don't assume this, please check out the DCC Systems comparison guide for more information. Some systems are still limited to 14 or 28 speed steps, not both at the same time. Some few manufacturers still make decoders that operate only in 28 speed step mode - for those, you may find it necessary to status edit the slot this locomotive uses in the command station.
[edit] Which is better?
There have been discussions over the years as to whether 128 speed steps are necessary or not. The nay-sayers would always say, "the real ones don't have 128 speed steps". Just keep in mind, these are not real trains, these are just models. And like everything that gets scaled, all things can't be scaled exactly the same and still appear the same. With model railroad control, the smaller the scale the more speed steps you need to have good control.
It could be argued that the disagreement had systems that didn't do 128 speed steps and others did. Being loyal to their system, those with non-128 speed step systems would argue that 128 speed steps weren't necessary. However, those that had systems capable of 128 speed step systems argued that it's the greatest thing since sl__(you get the idea).
[edit] Scale matters
As a general rule, the smaller the scale you operate, the finer the control needs to be to achieve realistic switching and other operations. While 28 speed steps may be OK for G scale, 128 is certainly a whole lot better for HO and N scales. Of course, if all you want to do is turn your trains on and watch them go, any amount of speed steps is fine.
