A circuit for digital signal processing calls for the use of a variable length instruction set. An exemplary DSP includes a set of three data buses (108, 110, 112) over which data may be exchanged with a register bank (120) and three data memories (102, 103, 104). A register bank may be used that has registers accessible by at least two processing units (128, 130). An instruction fetch unit (156)may be included that receives instructions of variable length stored in an instruction memory (152). The instruction memory may be separate from the set of three data memories (102, 103, 104).