Lighting control · 8 minute read
DMX addressing explained: fixture footprints, universes and DIP switches
A DMX start address is only the first slot a fixture listens to. To patch a rig correctly, you also need the fixture mode’s channel footprint, the last occupied slot and the addressing convention used by the fixture or controller.
Start address and footprint answer different questions
The start address identifies the first control slot assigned to a fixture. The footprint is the consecutive number of slots consumed by its selected operating mode or personality. A fixture starting at 101 with a six-address footprint occupies slots 101 through 106.
Changing from a basic mode to an extended mode can change the footprint, so the next fixture’s start address may need to move even when the physical fixture has not changed.
Calculate the occupied range before the next start
The final occupied slot is start address + footprint − 1. With no deliberate gap, the next fixture starts at the previous start plus the footprint. For three six-channel fixtures beginning at 101, the occupied ranges are 101–106, 107–112 and 113–118.
Document the selected mode beside every fixture. A patch sheet containing only start addresses cannot reveal whether two ranges overlap after someone changes a mode.
- Fixture and position
- Selected mode
- Universe
- Start address
- Footprint
- Final occupied slot
Keep a fixture intact at a universe boundary
A DMX universe provides 512 addresses, each carrying an 8-bit value from 0 through 255. A 16-address fixture can begin at 497 and finish exactly at 512. If its footprint would extend past 512, place that fixture intact in the next universe rather than splitting one operating mode across two universes unless the equipment documentation explicitly supports it.
Universe numbering and network transport configuration are separate from the slot calculation. Confirm the controller, gateway and node mappings when sACN, Art-Net or another network layer is involved.
DIP switches encode powers of two—but conventions vary
A common nine-switch address bank represents the values 1, 2, 4, 8, 16, 32, 64, 128 and 256. To encode direct address 101, combine 64 + 32 + 4 + 1, which turns on switches 7, 6, 3 and 1 when switches are numbered from the least-significant value.
Nine binary switches represent values 0 through 511, so a direct-value bank cannot express address 512. Some fixtures instead use an address-minus-one offset, reverse the physical switch order or reserve an additional switch for another function. Never infer that convention: the fixture manual remains authoritative.