NMRA CV 1 - Short Address (Primary Address)
When programming a decoder address, there are two address "ranges" you can program: Two-digit "Short" addresses, and Four-digit "Long" addresses. The word "digit" refers to the number of 4-bit "nibbles" used to represent the address in binary. The word "digit" does not mean there needs to be specific numbers in your address! The address type, short or long, is select-able using CV 29. By default, a decoder ships in the two-digit "short" addressing format with a value of 3 in CV 1.
Note: A DCC decoder will operate out of the package on Short Address 3 with no programming required per NMRA requirement.
The two-digit "Short" address is stored in CV1 and has a valid range of values from 1 to 127. A value higher than 127 is invalid for short addressing. If you would like to program your locomotive with an address (such as a road number) which is greater than 127, you must use a 4-digit "Long" address. Per the NMRA spec, CV1 cannot be modified on the main via operations (OPS) mode programming; therefore, you MUST use a dedicated DCC programming track to make that change.
A value of 0 in CV 1 will enable "power source conversion" if supported by the decoder.