Fill level capture in a buffer

An address generator (40) comprises a read address register (21), a write address register (11), at least one counter (13, 16, 23, 26) for incrementing the registers (21, 11) after each issuance of a read or write register A write address, a level register (30), and means (31) for incrementing the level register (30) each at the time of outputting a write address and for decrementing the level register (30) each time a read address is output.