Using 128 speed step decoders with E-Z Command

[Jim Banner]

There seems to be some confusion about what "28/128 Speed Step Control" really means and how this relates to using a Bachmann E-Z Command with 128 speed step decoders.  I hope to shed a little light on the situation.

Early decoders had only 14 speed steps.  The speed information was stored in half a register with headlight control stored in the other half of the same register.  This gave pretty big changes in speed when you changed your throttle from one step to the next.  Using more, smaller steps would smooth out the changes.  But this required an additional register in the decoder to store the longer speed commands and a switch to tell the decoder which register to look in and how to interpret what it found.  The first improvement was to double the number of speed steps to 28.  But having a whole register dedicated to speed commands allowed an even greater number of speed steps, such as 128 steps, to be stored.  The switch that we use to tell the decoder which type of speed steps it was dealing with is bit 1 in CV29.  When it is 0, the decoder uses 14 speed steps.  When it is one, the decoder uses 28 OR 128 speed steps.  So those are the two possible modes - 14 Speed Step Control and 28/128 Speed Step Control.

When Bachmann tells us that the E-Z Command can work with 28/128 Speed Step Control, it does NOT mean it can produce 128 speed steps.  It might make more sense if this mode were called "Extended Speed Step Control" or "Advanced Speed Step Control" because there would not have been any implication of the exact number of speed steps that it used.  Unfortunately, the term 28/128 Speed Step Control had already been adopted by others and Bachmann just followed suit.  Just like with that confusing term "DCC Ready."

Recently, there has been some controversy about just how many speed steps E-Z Command really does produce.  It was suggested that perhaps it produced 56 speed steps, the standard 28 steps plus 28 more intermediate steps generated by rapidly switching back and forth between two speeds.  I checked that this evening by connecting an E-Z Command to a decoder set to 128 speed steps.  With the decoder's output connected to a locomotive's motor and to a voltmeter, it was easy to check how many steps were generated when advancing the throttle from 0 to full throttle.  There were 25 steps.  Why not 28? probably because the last three got lost when the motor pulses became a continuous dc level at little early, at step 25 instead of step 28.  Unless the E-Z Command design has been recently modified, I suspect all E-Z Commands produce about 28 steps in 28/128 Speed Step Control Mode.

In another thread, I suggested that an E-Z Command could still be used to produce smooth, 128 speed step control by setting an acceleration rate in a 128 speed step decoder.  When the speed knob was turned, it would send a desired speed to the decoder and the decoder would accelerated to that speed at the 128 speed step rate.  Suppose for example you gave a locomotive 1/8 more throttle.  At 25 speed steps for the whole throttle, the locomotive's speed would increase in 25/8 = 3 big steps.  But with the decoder accelerating at the 128 speed step rate, the locomotive's speed would increase the same amount in 128/8 = 16 small steps.  The result would be a smoother acceleration.  After this evening's bench testing, it turned out I was partly right.  Using a Digitrax DZ123 decoder set for 128 speed steps, I measured the number of steps it took to accelerate from zero to full throttle.  Surprisingly, it took not 128 steps but 220 steps.  I have a strong suspicion this decoder was working internally at a 256 speed step rate but losing 10% or so of the steps at the top end as explained previously.  Even just using 220 steps, that 1/8 increase in throttle would increase the speed in 220/8 = 28 tiny steps.  In other words, very, very smooth acceleration, the sort of smoothness you would expect from a 256 speed step decoder.

Bottom line, these tests indicate that an easy way to get super smooth acceleration using your E-Z Command is to use a 128 speed step decoder with some acceleration programmed in.

Jim   

[jonathan]

Thanks, Jim!

As always, you have a way of explaining things so even my simple mind can understand what's going on.

Regards,

Jonathan

[Hunt]

. . .
When Bachmann tells us that the E-Z Command can work with 28/128 Speed Step Control, it does NOT mean it can produce 128 speed steps.
. . .

Jim,
As you and the folks at Bachmann know, I disagree.

I have been in DCC for nearly two decades. With the exception of what I just quoted you wrote, everyone with some knowledge of DCC I have spoken with over the last several years agree with the following.

A DCC command station having a feature of 28/128 speed step control shall be capable of the end user selecting between  28 and 128 speed step command to be sent to a decoder address. A 28/128 speed step decoder as set by CV 29 shall automatically handle 28 and 128 speed step command sent to it.  

A DCC command station capable of only 28 speed step control shall not be promoted as having a feature of  28/128 speed step control but as having a feature of 28 speed step control.

Bachmann had been promoting their E-Z Command Control Center, Item No. 44902,    
Features include:
 •  28/128 speed step control

Appropriately, Bachmann has now started in the 2011 print catalog promoting the E-Z Command Control Center,
Features include:
  • 28 speed step control

[NarrowMinded]

Thanks Jim,
I think that explains why there is no detectable differance in operation when I switch to the EZ command so my little ones can run trains.

NM

[Doneldon]

Hunt-

I don't know if your post got garbled by the computers
or what but I don't understand what you wrote. What
were you trying to say?
                                              -- D