A programmable logic device has a plurality of conductors extending around its periphery for use in providing at least some of the signals needed for control of input/output ("I/O") pins which are also disposed around the periphery of the device. These control signals may include clock signals, output...http://www.google.com.au/patents/US6107825?utm_source=gb-gplus-sharePatent US6107825 - Input/output circuitry for programmable logic devices
