1. An apparatus for generating routing information and for adding said information to a block of digitized data being sent from a source of such data to a utilization device for such data, said apparatus comprising: first storage means responsive to said source of digitized data for storing a first segment of said data block; a first addressable memory responsive to the data contained in said first storage means for providing predetermined data signals; means having input, output, and control terminals, responsive to said predetermined data signals of said first memory applied to its control terminals, for selecting data to be applied to its output terminals from among data of a second segment of said data block, being applied to its input terminals; a second addressable memory, having output terminals, said second addressable memory coupled to said first storage means and said data selecting means for providing at its output terminals a data word accessed from said second memory in response to an address formed by the data stored in said first storage means and the selected data at the output terminals of said selecting means; means coupled to said output terminals of said second memory and responsive to values of said data word accessed from said second memory for generating a plurality of control signals; generator means coupled to said second memory and responsive to a first one of said plurality of control signals for transferring a data word stored in said generator means to said second memory for storage therein at said address formed by the data stored in said first storage means and the selected data at the output terminals of said selecting means; means coupled to said second memory and to said first storage means and responsive to second one of said plurality of control signals for replacing the data stored in said first storage means by said data word accessed from said second memory for causing a data word to be accessed from said second addressable memory in a subsequent cycle of data transfer; and means responsive to a third one of said plurality of control signals for combining said data word accessed from said second memory with said block of digitized data for transmission to said utilization device.