The XC4000 families of Field-Programmable Gate Arrays (FPGAs) provide the benefits of custom CMOS VLSI, while avoiding the initial cost, time delay, and inherent risk of a conventional masked gate array. The XC4000 families provide a regular, flexible, programmable architecture of Configurable Logic Blocks (CLBs), interconnected by a powerful hierarchy of versatile routing resources, and surrounded by a perimeter of programmable Input/Output Blocks (IOBs). XC4000-family devices have generous routing resources to accommodate the most complex interconnect patterns. 

XC4000A devices have reduced sets of routing resources, sufficient for their smaller size. XC4000H high I/O devices maintain the same routing resources and CLB structure as the XC4000 family, while nearly doubling the available I/O. The devices are customized by loading configuration data into the internal memory cells. The FPGA can either actively read its configuration data out of external serial or byteparallel PROM (master modes), or the configuration data can be written into the FPGA (slave and peripheral modes). 

The XC4000 families are supported by powerful and sophisticated software, covering every aspect of design: from schematic entry, to simulation, to automatic block placement and routing of interconnects, and finally the creation of the configuration bit stream. 

Since Xilinx FPGAs can be reprogrammed an unlimited number of times, they can be used in innovative designs where hardware is changed dynamically, or where hardware must be adapted to different user applications. FPGAs are ideal for shortening the design and development cycle, but they also offer a cost-effective solution for production rates well beyond 1000 systems per month.