Editing DMX512 (section)

=== Addressing and data encoding ===
Most data is sent with the default Null Start Code of 00h. Quoting from the standard:
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8.5.1 NULL START code

A NULL START Code identifies subsequent data slots as a block of un-typed sequential 8-bit information.

Packets identified by a NULL START Code are the default packets sent on DMX512 networks. Earlier versions of this standard assumed that only dimmer class data would be sent using NULL START Code packets. In practice NULL START Code packets have been used by a wide variety of devices; this version recognizes this fact.

Each NULL START Code packet contains no formal data or addressing structure. The device using data from the packet must know the position of that data within the packet.}}

Dimmer packs or racks use a group of slots to determine the levels for their dimmers. Typically a dimmer has a starting address that represents the lowest-numbered dimmer in that pack, and the addressing increases from there to the highest-numbered dimmer. As an example, for two packs of six dimmers each, the first pack would start at address 1 and the second pack at address 7. Each slot in the DMX512 packet corresponds to one dimmer.

==== 8-bit v. 16-bit ====
DMX does not mandate a method of 16-bit encoding for Null Start Code packets; however, many parameters of moving lights make use of encoding larger than 8-bit numbers. To control these parameters more accurately, some fixtures use two channels for parameters that require greater accuracy. The first of the two channels controls the coarse (256 steps for the whole range of movement) and the second the fine (256 steps for each coarse step), this gives a 16-bit value range of 65536 steps, permitting much greater accuracy for any 16-bit controlled parameter such as Pan or Tilt.