DCC Impulses Column - 2
1. The programming track station and selector switch at the
PebbleCreek Model Railroad Club.
1
A tale of two worlds
At this juncture, I’m reminded of the joke about people: “There
are two kinds of people in this world, those who divide the
world into two sections and those who don’t.”
There are two ways of programming and two kinds of program-
ming track and two ways of programming on-the-main. And
just to make things interesting, different manufacturers use dif-
ferent names for the same thing.
One way: on a programming track
Sometimes referred to as service mode programming, pro-
gramming on the programming track is where you can write to
and read from your decoder on a dedicated track.
The command station function of your DCC system (see my
column “Anatomy of a DCC System”
is respon-
sible for controlling the programming track: the command sta-
tion turns on and off the power to it, monitors the current flow
into it, sends commands to it, and receives acknowledgements
(ACK pulses) back from it. ACKs are the decoder’s way of talk-
ing to the command station.
The programming track must be isolated from the remainder of
the layout in order for the ACKs to be heard by the command
station. The electronics that drives the programming track is
not protected against current flowing from the track back into
the command station. This back flow would happen if the pro-
gramming track were to be connected to the layout DCC signal.
The programming track must never be connected, even one rail
at a time, to the layout track or bus.
Never is never; not for even a fraction of a second. You may get
away with a “5-second” rule when you drop your sandwich,
but not here.
There are multiple modes or languages that may be utilized
in this dialog between the command station and the decoder.
Here are some of the modes, with the abbreviation shown on
Digitrax’ DT4xx series throttles:
Address Mode is an early programming method in the NMRA
standards. It is outdated and modern decoders have no rea-
son to go there.
Register Mode (Ph in Digitrax parlance) grew out of Address
Mode. It is a very limited way to access a few CVs. It is mostly
extinct, too. A few older and low end decoders need to be
accessed this way.
Paged Mode (Pg in Digitrax parlance) grew out of Register
Mode. It allows access to virtually all CVs. Of the two mod-
ern programming modes, Paged Mode is significantly slower
than Direct Mode. Per their web site
, Paged Mode is “Digitrax
Preferred Programming Mode”.
MRH-May 2014
