Abstract: Method and apparatus for generating unique addresses for each of a plurality of circuit units (4-1 to 4-n) coupled to a single path (2) at individual spaced, coupling points along its length wherein a control circuit (1) transmits an address generation signal along the path (2). At each coupling point in turn the circuit unit modifies the address generation signal received so that a succeeding circuit unit receives modified, unmodified, or both modified and unmodified address generation signals dependent on the position of the circuit unit and on the form the modification takes. Various modifications are described including interrupting the passage of the address generation signal for a predetermined time and adding elements to the address generation signal.