Data formatting apparatus for formatting variable bit length data words into successive fixed bit length data words comprises an N-bit circular buffer (160) comprising a plurality of concatenated buffer sections, each buffer section having the same bit length as one of the fixed bit length data words. A modulo-N counter (120) generates a count of the cumulative length of received variable bit length data words. Each received variable bit length data word is stored in the N-bit circular buffer (160) at a bit position dependent on the count signal, and, in response to a detection that data has been stored in all of the bits of that buffer section, the stored data from that buffer section is output as a fixed bit length data word. <IMAGE>