Abstract: In order to keep the number of data transfers small in storing bit pattern fields in an external memory, only the first line and the changed data of the bit pattern field are transmitted and the field is reconstructed line by line by means of an interim register and then stored. For this purpose the interim register has, besides a data input connected with the bit pattern field and an input for a STROBE signal, an input for addressing register locations corresponding to those memory building blocks, the data of which has changed from line to line. Advantageously, groups of eight memory building blocks, to which an interim register in the form of an 8-bit decoder register is assigned, are used.