1. A method of operating a machine, the method comprising a sequence of steps performed by the machine, each step in the sequence comprising substeps of: using an input signal received by the machine to obtain a received signal, the received signal being a data item having a value that is one of two or more possible received values; obtaining a control data item using said received signal; the control data item having one of a set of control values including a first control value and a second control value; if said control data item has the first control value, using said received signal to generate a generated data item having one of two or more possible generated values; and if said control data item has the second control value, storing the generated data item of a preceding step in the sequence so that the preceding step's generated data item can be accessed using a data item having the value of the preceding step's received signal.