An integrated circuit comprises a predefined logic area including a microprocessor coupled to a plurality of peripheral devices including an external bus interface over a system bus. A customizable logic area is accessible by the microprocessor over the system bus. A first I/O bus sends data to an external device. A second I/O bus receives data from an external device. A first set of multiplexers in the predefined logic area have first inputs coupled to an output of the external bus interface, second inputs coupled to the customizable logic area, and an output coupled to a first I/O bus. A second set of multiplexers in the predefined logic area have first inputs coupled to the customizable logic area, second inputs coupled to the second I/O bus, and an output coupled to an input of the external bus interface.