A programmable data processing circuit has a memory for storing pixel values, or more generally data values as a function of position in a signal. The programmable data processing circuit supports instructions that include an indication of a selected parameter value set that indicates how a plurality of data values must be arranged for parallel output from a memory. Instructions that indicate different parameter value sets can be executed intermixed with one another. The programmable data processing circuit responds to instructions of this type by retrieving the selected parameter value sets from a parameter storage circuit (246), and controlling a switching circuit (22) between a memory port (21) of a memory circuit (20) and a data port (26) at least partly dependent on the selected parameter value set.