Abstract: Methods and structures utilizing multiple configuration bitstreams to program integrated circuits (ICs) such as programmable logic devices, thereby enabling the utilization of partially defective ICs. A user design is implemented two or more times, preferably utilizing different programmable resources as much as possible in each configuration bitstream. The resulting user configuration bitstreams are stored along with associated test bitstreams in a memory device, e.g., a programmable read-only memory (PROM). Under the control of a configuration control circuit or device, the test bitstreams are loaded into a partially defective IC and tested using an automated testing procedure. When a test bitstream is found that enables the associated user design to function correctly in the programmed IC, i.e.

Abstract: A multi-state input drive structure is provided to forward externally generated high and low input signals, as well as to receive at least a third, internally generated, comparatively weak signal, preferably an oscillating signal, which triggers a third internally forwarded signal when neither of the high and low input signals is received. The inventive circuit drives three internally forwarded output signals from a single external signal source. Since this circuit may be duplicated for every pin on a device for which two cycle delays do not affect performance, availability of a third input state on N inputs allows 3.sup.N input codes as opposed to 2.sup.N for the conventional "high" and "low" levels normally available.