1.3 Locomotive addresses in the digital plus systemFour-digit addressing was added in XpressNet V3.0. This has had consequences in the way that datacommunication on XpressNet occurs. The locomotive addresses 0 to 99, used prior to V3, can betransmitted in a single byte, which can take 256 different values (8 bits). This is not sufficient however for locomotive addresses from 0 to 9999, which require two bytes. The following views and computations are indicated in hexadecimals, since this permits a better representation.In the NMRA specifications, short locomotive addresses and long locomotive addresses aredifferentiated. The short addresses (a single byte) have a range from 1 to 127 decimal. the longlocomotive addresses (2 bytes) from 0 to 16383 decimal. The short addresses thus requires 7 bits totransmit, the long addresses requires 14 bits to be transmitted. The overlap between short and longaddresses can become complicated and confusing for the user. To avoid this confusion XpressNet wasdesigned so that the locomotive addresses from 1 to 99 are always short addresses and the locomotiveaddresses from 100 to 9999 are always long addresses. For operation and information instructions,address 0 is used to define the operation of a non-decoder equipped locomotive (controlled using analog DC).The representation of the short addresses is simple: 0 to 99 decimal results in 0x00 to 0x63 hex.With the long addresses the two highest bits of the High bytes are set to 1. I.e. the locomotive addresswith 14 bits length has an additional offset of 0xC000 hex. Thus: Locomotive address 100 to 9999 is0xC064 to 0xE70F.
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