There is disclosed a controller for controlling two or more groups of nozzles in an array, the controller configured to: encode data blocks into a data stream, wherein each data block denotes how a respective group of nozzles is to be controlled for a droplet period; encode fire codes into the data stream, wherein each fire code is a reserved code that denotes when a respective group of nozzles is to be controlled in accordance with the data block for the droplet period; and wherein the data block precedes the fire code for the respective group of nozzles in the data stream and wherein the fire codes are generated independently of the data blocks.