118
Choosing the Locomotive Decoder Update Rate
The rate at which the Command Station sends out decoder speed and function updates is called
the "update rate." The rate is selectable from very fast to very slow. This "update rate" is
important since it is what restores the current speed to a locomotive that is coasting or stopped
following a power interruption. Locomotives are updated at the update rate as long as the
associated throttle speed is not zero. If the speed goes to zero, the locomotive address is updated
for an additional 2 minutes before it is declared inactive and updates stop.
What is Update Rate
The illustration below shows what happens over time when the decoder signal is interrupted. The
line labeled “Decoder Power” is used as an indication of what is happening over time. “Normal”
means the locomotive is running normally. Then, the decoder signal is “Interrupted” due to dirty
wheels or dirty track or a dead section of track. After a short period of time decoder signal is
restored back to “Normal.” For very short interruptions, the locomotive might coast for a fraction
of a second. However a long power interruption will result in the decoder having to reinitialize
and then wait for the DCC signal with its address to come along.
The second line shows what is happening inside the decoder for a power interruption that causes
the decoder to restart. Notice during the power interruption, the decoder is basically dead. It is as
if you just turned on the track power. When power is restored, the decoder resets the motor speed
to zero. Now the decoder is ready and waiting for the DCC signal having its speed and direction.
When it arrives the decoder resumes running.
The third line shows what is happening at the Command Station. Each active locomotive with a
non-zero speed is periodically sent an update signal. The update rate is what is used to determine
how often this signal is sent. In the “Fast Update Example” the decoder has only a short time to
wait until its own DCC signal is received.
Update Frequency - Faster Is Not Always Better
Frequent updates can slow down the overall system response since the system is busy sending
out lots of updates. As a result, locomotive decoders will quickly return to their previous speed if
they encounter momentary power interruptions. These interruptions are most commonly caused
by dirty track, dirty wheels, dirty pickups, and track imperfections. Flickering headlights are a
sure sign of dirty track and wheels. A faster update rate may be used when there are relatively few
active locomotives. But a large number of active locomotives will incur a longer delay and the
overall system performance will slow down. For this type of layout, a slower update rate may be
best.
Fewer Updates Has Consequences Too
Less frequent updates improve the system response because the system has more time to spend
processing and handling new commands. Speed changes and function commands are
transmitted quicker. But, relatively clean track and wheels are a must since there will be a longer
delay following power interruptions.
continued on next page
Normal
Normal
Update UpdateUpdate UpdateUpdate UpdateUpdate Update
Normal
Ready Run
Power
Interruption
Dead
Reset
Decoder
Power
Decoder
Response
DCC Track
Signal
Fast Update Rate Example
To Next Page
Loading...
Need help?
General