On Termination, Part One
(This is an old post, but I do plan on posting an update, someday, when I get a digital scope.) [lighting nerd speak] The USITT PLASA specification for DMX-512A requires that the last physical device in any DMX link, whether it connects to one device or 31 others, be terminated with a 120Ω resistor. This is to prevent unwanted “reflections” coming down the line and corrupting the DMX data. Here’s the theory: DMX-512 signals travel at around 60% the speed of light. Although fast, this is not instantaneous. When a signal traveling at over half the speed of light hits the end of a cable, a percentage of the signal is reflected back down the signal chain. Each digit of… Read More »On Termination, Part One