address came about. Why is “4-digit” incorrect? Because there
are at least 871 3-digit addresses that fall in to the long address
realm. Addresses from 128 to 999 must be long addresses, but
only have three digits. See figure 2 for an example.
However, the designers didn’t make it as simple as it could
have been and put two digits in CV 17 and the other two dig-
its in CV 18. No, there is a complicated formula for what is
stored in the two CVs so the decoder knows its name. NMRA
Recommended Practice (RP) 9.2.2 allows long addresses from
0 to 10239. I don’t know of a system that currently addresses
locos above 9999, though. More on this later.
The decoder needs to know what name (address) to respond
to: the short address in CV 1 or the long address in CVs 17
& 18. This is sort of like my Tom and Thomas analogy above.
DCC Impulses Column - 2
1: Loco with a short cab address of 4 – I run it as a long
address on NCE by programming it as a long address and
selecting it as 04.
1
2: Loco with cab address of 268 – this will be a long address
on any system, even though it has only 3 digits.
2
Types of Addresses
There are three types of addresses:
Short, stored in CV 1
Long, stored in CVs 17 & 18
Consist, stored in CV 19
Initially, DCC systems only recognized addresses from 1 to 127
and they were stored in CV 1. Storing a value of zero (0) in CV1
will force the decoder OUT of DCC mode and into using an alter-
nate power source defined by CV 12. Usually that is DC mode.
It was realized quickly that limiting the system to 127 rather
arbitrary numbers was a serious limitation and the concept of
the long, or extended, (sometimes incorrectly called 4-digit)
MRH-Feb 2014
