1. A mask programmable integrated circuit (IC) for replacing a field programmable gate array (FPGA), the FGPA having a set of input/output (I/O) blocks, the IC comprising: a gate array core; and a set of mask programmable I/O cells providing an interface between signals in said core and signals outside the IC, said I/O cells having I/O characteristics similar to those of the FPGA I/O blocks such that substitution of the IC for the FPGA does not require other chances to a system in which the substitution is made.