It depends which build level you've got though. Earlier ones were designed only to run from a controller, later Martin units had the extra chip required to 'retransmit' master data to slaves. You can tell because on the earlier (non master-slave) versions, there is direct continuity between the in and out DMX XLR pins, on later ones there isnt.
In the heyday of the Roboscan 812, the Master-Slave thing was pretty much for 'DJ' products and units of Martin's class were expected to be operated from a controller in an expensive installation...either the Martin own-brand unit or, most commonly, a Pulsar Masterpiece.
Martin dealer controller recommendationWhy not get a cheap Martin RS485 controller off ebay? No-one wants them these days though they are very easy to use if you have 'all martin' stuff and they are built like tanks, dead reliable..??